msomi maktaba

# FORM 6 PHYSICS: ENVIROMENTAL PHYSICS PART – 3

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THE EARTH’S MAGNETIC FIELD

Â The earth has a weak magnetic field, 95% of this field is created inside the Earth’s core 5% is the result of atmospheric effects above the Earth’s surface.

GeomagnetismÂ is science of study of the earth magnetic field, its causes and its variations.

Generation of the Earth’s magnetic field within the core

The accepted explanation for the origin of the Earth’s magnetic field within the core is given by Lemoir’s self exciting dynamo theory.

Â  The Earth’s Outer Core consists of molten conducting metals (Iron and Nickel) which are rich in free electrons.Â  The Earth’s rotation causes the molten metal to rotate and hence large convection currents are set up within the outer core.Â  These currents generate a magnetic field.

Â  Eddy currents are now generated due to a conducting material moving in a magnetic field.Â  These Eddy currents modify the position of the Earth’s magnetic field so that it does not lie along the Earth’s axis of rotation.Â  The present magnetic poles are situated 800km from the Earth’s axis.

Generation of magnetic field in the Atmosphere

Â In the Earth’s atmosphere there is a region know as the ionosphere which consists of free electrons and ions. The movement of these charges creates a magnetic field.Â  This effect provides a small fraction of the Earth’s total magnetic field.

TERMS ASSOCIATED WITH THE EARTH’S MAGNETIC FIELD

Â Magnetic meridian:Â A vertical plane passing through the axis of a freely suspended magnetic needle.

Â Geographic meridian:Â  A vertical plane passing through the geographic axis.

Â Magnetic equator:Â  Is the locus of points on earth’s surface where the needle (free to rotate in a vertical plane) remains horizontal.

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The Earth’s magnetic field pattern is similar to that produced by a giant bar magnet or solenoid.

Note:Â  (i)Â  The magnetic North pole which lies in the Northern Hemisphere behaves like a south pole or a bar magnet, i.e. the field lines are directed towards it.

Â Â Â Â  (ii)Â  The magnetic south pole which lies in the southern hemisphere behaves like a north pole of a bar magnet, i.e. the field lines are directed away from it.

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ELEMENTS OF EARTH’S MAGNETISM

Angle of variation of declination, at a place is the angle between the geographic meridian and the magnetic meridian at that place.

Angle of dip or declination, at a place is the angle between the directions of intensity of the earth’s total magnetic field declinationand the horizontal direction, in the magnetic meridian at that place.

Horizontal component of Earth magnetic field It is the component of the Earth’s total magnetic field along the horizontal direction in the magnetic meridian.

By Pythagoras theorem

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By trigonometric ratio

Points to note about angle of Dip

(a)Â  At the poles,

Therefore, only horizontal component exists at the poles

Â (b)Â  At the equator

At the equator only horizontal component exist.

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VARIATIONS OF THE EARTH’S MAGNETIC FIELD

The Earth’s magnetic field is not constant but varies continuously with time.

(i) Short term variations (Irregular changes):Â  The magnetic field changes daily due to variations in the magnetic field created in the ionosphere.Â  The charged particles in this region of the atmosphere are affected by the Sun’s gravitational pull (which is stronger when the sun is directly above that area)

Â Also during periods of high solar activity charged particles from the solar wind are able to penetrate the magneto pause and arrange themselves under the influence of the magnetic field in a formation called Van Allen Belts.Â
Â These charged particles cause further Eddy currents within the ionosphere, altering the Earth’s magnetic field strength.

Â Solar wind is a continuous stream of moving electrons and protons in the atmosphere which are produced from flare (eruptions) from the sun.Â  Normally these charged particles move from west to south at 300 â€“ 500 km/s.

Magnetic storm is a sudden worldwide disturbance of the earth’s magnetic field caused by dynamic interaction of the earth’s magnetic field and the sun.Â  During magnetic storm, the earth’s magnetic field is unusually active.

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Effects of Magnetic Storm

(a)Â Â  Large storms can cause the loss of radio communication

(b)Â  Damage satellite electronics and affect satellite operations.

(c)Â Â  Increase pipeline corrosion

(d)Â  Induce voltage surges in electric power grids causing blackouts.

(e)Â Â  Reduce the accuracy of global positioning systems.

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(ii) Long term variations (Secular changes):Â  The Earth’s magnetic field position is constantly changing, now the magnetic North pole is moving at 8 km per year, and the magnetic South Pole at 16 km per year.

Evidence from the alignment of magnetized rocks layers in the Earth’s crust show that the Earth’s magnetic field has actually reversed in direction several times during the Earth’s history (i.e. the direction of the fields have reversed causing a north acting pole to become a south acting pole.) Â The present polarity of the Earth’s magnetic field has not changed for 700,000 years.

VAN ALLEN BELTS

The Van Allen belts consist of two regions of highly charged particles which are trapped within the Earth’s magnetic field:

Inner BeltÂ consists of protons and positive charged particles

Outer BeltÂ consists of electrons and negatively charged particles.

THE ATMOSPHERE

Earth’s atmosphere is divided into five main layers, the exosphere, the thermosphere, the mesosphere, the stratosphere and the troposphere.Â  The atmosphere thins out in each higher layer until the gases dissipate in space.Â  There is no distinct boundary between the atmosphere and space, but an imaginary line about 110 kilometers from the surface, called the Karman line, is usually where scientists say atmosphere meets outer space.

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TROPOSPHERE

The troposphere is the layer closest to Earth’s surface.Â  It is 10 km thick and contains half of Earth’s atmosphere.Â  Air is warmer near the ground and gets colder higher up.Â  Nearly all of the water vapor and dust in the atmosphere are in this layer and that is why clouds are found here.

Lapse rateÂ is the rate of fall of temperature in degrees per kilometer rise.Â  It has an average value of 6 0C per km in the troposphere.

Â TropopauseÂ is the upper boundary of the troposphere.

Importance (uses) of troposphere

1.Â Â  Controls the climate and ultimately determines the quality of life in the atmosphere.

2.Â Â Â  It supports life on earth.Â  It contains oxygen which is used to respiration by animals.

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STRATOSPHERE

Â The stratosphereÂ is the second layer.Â  It starts above the troposphere and ends about 50 km above ground.

Â The temperature of the stratosphere slowly increases with altitude.Â  This temperature increase is due to the presence of Ozone layer which absorbs heat from the sun in the form of ultraviolet light.

The Ozone layer occupies the middle of stratosphere between 20 and 30 km it consists of Ozone formed by oxygen molecules dissociated and reforming into 03.

Â The air here is very dry, and it is about a thousand times thinner here than it is at sea level.Â  Because of that, this is where jet aircraft and weather balloons fly.

StratopauseÂ is the upper boundary of the stratosphere.

Â Importance (uses) of stratosphere

The stratosphere prevents harmful ultraviolet radiation from reaching the earth.Â  Ozone absorbs harmful radiation from the sun.Â  The Ozone protects plants and shield people from skin cancer and eye cataracts.

Â MESOSPHERE

Â The mesosphere starts at 50 km and extends to 80 km high.Â  The top of the mesosphere, called the mesopause, is the coldest part of the Earth’s atmosphere with temperatures averaging about – 900C.Â  The temperature of the mesosphere decreases with altitude (because there is no ozone to absorb heat).

Â This layer is hard to study.Â  Jets and balloons don’t go high enough, and satellites and space shuttles orbit too high.Â  Scientists do know that meteors burn up in this layer.

Importance of mesosphere

Â Mesosphere, thermosphere and exosphere prevent harmful radiation such as cosmic rays from reaching the earth surface.

THERMOSPHERE

Â The thermosphere extends from about 80 km to between 500 and 1,000 km.Â  Temperatures increases as it approaches nearer to the sun. The heating effects of the earth no longer exist at these higher altitudes.

Â The thermosphere is considered part of Earth’s atmosphere (the upper atmosphere), but air density is so low that most of this layer is what is normally thought of as outer space.Â  In fact, this is where the space shuttles flew and where the International Space Station orbits Earth.

This is also the layer where the auroras occur.Â  Charged particles from space collide with atoms and molecules in the thermosphere, exciting them into higher states of energy.Â  The atoms shed this excess energy by emitting photons of light, which we see as the colorful Aurora Borealis and Aurora Australis.

EXOSPHERE

Â The exosphere, the highest layer, is extremely thin and is where the atmosphere merges into outer space.Â  It is composed of very widely dispersed particles of hydrogen and helium.

Â The upper part of the exosphere is called Magnetosphere.Â  The motion of ions in this region is strongly constrained by the presence of the earth’s magnetic field.Â  This is the region where satellites orbit the earth

Note:

(i)The troposphere, stratosphere, and mesosphere are collectively forms the homosphere.Â  These layers have the same chemical composition; 78% nitrogen, 21% oxygen, 1% argon and other gasses which sum to about 0.05%.Â  The thermosphere is excluded due to different in chemical composition.

(ii) The upper atmosphere above 90 km is called heterosphere. The atmosphere is no longer a mixture of gases but separates into layers heavier ones forming the bottom layer.

VARIATION OF TEMPERATURE WITH HEIGHT

The temperature above the Earth surface varies as shown in the graph below.

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The residence time,Â is the mean lifetime of a gas molecule in the atmosphereÂ

THE IONOSPHERE AND TRANSMISSION OF RADIO WAVES

The ionosphere is the region containing high concentrations of charged particles ions and electrons.

The ionosphere is created by atoms absorbing U.V radiation, gamma and X â€“ rays.

Â The ionosphere extends from the lower thermosphere 55 km to 550 km above the earth’s surface.

Ionosphere layers:

Due to difference in composition of the air in the ionosphere, the ionosphere is divided into layers.

(i)Â  Â  The lower layer, called D layer; this layer exists only in the day time at an altitude of 55 to 90 km above the earth’s surface. Ionization in this region is relatively weak.

(ii)Â  The next layer, E â€“ layer: this layer is between 90 and 145 km above the earth’s surface.Â  It has a maximum density at noon but is only weakly ionized at night.

(iii)Â Â  The top layer, the F â€“ layer:Â  At night exists as a single layer in a region of about 145 to 400 km above the earth’s surface.Â  During the day it splits into two layers, F1 and F2.Â Â

The Ionosphere and Communication

The ionosphere plays an important role in communication.Â  Radio waves can be reflected off the ionosphere allowing radio communications over long distances.Â  However this process is more successful during the night â€“ time.

Why Transmission is better at Night?

Â During the day:Â  the ionosphere extends into lower atmosphere (D layer).Â  In this layer there is high concentration of particles and so recombination of electrons and ions due to collision is more likely to occur. The leads to the radio waves being absorbed rather than reflected.Â  Hence distant communications are poor during the day.

Â During the night:Â The D layer disappears due to decrease in ionization of molecules but recombination of electrons and ions still occurs at a fast rate.Â  The radio waves are then reflected by E and F layers in which recombination of electrons and ions is rare hence there is less absorption of the radio waves.

EXAMPLES:Â  SET C

Example 01:Â  Necta 1985 P1

(a)Â  (i)Â  Distinguish between P and S waves, state clearly the difference between their speeds in a medium.

Â  Â  Â  Â  Â  Â  (ii)Draw a schematic diagram showing how one station on the Earth’s surface can receive P or S waves from a distant source and state which waves can be refracted by the Earth’s outer core.

(b)Â  (i)Â  Give a summary of the origin and composition of the ionosphere.

Â Â Â Â Â  (ii)Â  What is the net electric charge in the ionosphere?

Â Â Â Â  (iii)Â  Show graphically how electron density changes with altitude in the ionosphere.

(a)Â Â Â Â  (i)Â  P â€“ waves are longitudinal compression waves which can pass through solid, gas and liquid, whereas S – waves are transverse shearing waves which cannot pass thorough a fluid (gas or liquid)

The speed of P â€“ waves in a medium is approximately twice that of the S â€“ waves hence P â€“ waves are faster than S â€“ waves.

(ii)Â  Refer the diagram for the seismic wave paths

(b)Â Â Â Â  (i)Â  Ionosphere is the upper part of the atmosphere.Â  The ionosphere is formed due to the ionization of gaseous atoms as they absorb ultraviolet radiation from the sun, gamma and X-rays.

(ii)Â  The net electric charge in the ionosphere is zero.

(iii) Variations of electron density in the ionosphere Electron density increases from D to F layerÂ

Example 02:Â  Necta 1988/1993 P1

(a)Â Â  What are the factors that influence the velocities of P â€“ and S â€“ waves?

(b)Â  Explain briefly the characteristics property of seismic waves which is used to locate discontinuities in the earth’s crust.

(a)Â  The velocities of both P and S â€“ waves are influenced by;

(i)Â  Density of the rock material (Media),

(ii)Â  Moduli of elasticity.

(b)Â  Speed is the characteristic property of seismic waves that is used to locate discontinuities

Between the crust and mantle there is abrupt change of density, which shows an abrupt change in speed of both P â€“ and S â€“ waves, a Mohorovicic discontinuity exists here.Â  Both P â€“ and SÂ

waves travels across this discontinuity.

Between the mantle and the core there is the Gutenberg discontinuity only P â€“ waves travel this discontinuity.

Example 03: Necta 1989 P1

(a)Â Â  State three sources of heat energy in the interior of the earth.

(b)Â  (i)Â  How does temperature vary with depth of the Earth?

(ii)Â  What are the factors that influence the flow of heat from the interior of the Earth?

(a)Â  Refer notes

(b)Â  (i)Â  The temperature increases with increasing depth

Â Â Â Â Â  (ii)Â  The rate of heat flow (conduction) is given by

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The heat flow from the interior of the earth depends on:

Â Â Â Â Â Â Â Â  Thermal conductivity of the rock,

Â Â Â Â Â Â Â  Temperature gradient of the rock

Example 04:Â  Necta 1989 P2

(a)Â  What do you understand by the terms?

(i)Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  Solar wind,

(ii)Â Â Â Â Â Â Â Â Â Â Â Â  Magnetopause

(iii)Â Â Â Â Â Â Â Â Â Â  Magnetosphere?

(b)Â  What are the various factors that contribute to the Earth’s magnetic field?

(c)Â  (i)Â  With the aid of a suitable diagram, illustrate the components of the earth’s magnetic field at a given point P in the earth’s atmosphere.

(ii)Â  An electron whose kinetic energy is 10 eV is circulating at right angles to the earth’s magnetic field whose uniform induction is 1.0 x 10 Wbm-2.Â  Calculate the radius of the orbit and its frequency in that orbit.Â

(a)Â Â  (i)Â  Solar wind is a continuous stream of fast moving charged particles in the atmosphere which are produced from flare (eruptions) from the sun:

(ii)Â  Magnetopause is the upper boundary of the magnetosphere.

(iii) Magnetosphere is the upper most part of the exosphere consisting mainly of charged ions.Â  These particles move under the influence of the earth’s magnetic field.

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(b)Â Â  Short term variations:Â  Disturbances in the magnetosphere due to solar emissions, these charged ions travel and in the ionosphere they form ring currents which give rise to a magnetic field.

Long term variations:Â  The molten inner core of the earth is partly ionized.Â  The movement of this ionized core causes a magnetic field which contributes to the earth’s magnetic field.

(c)Â Â  (i)Â  refer notes (ii)Â  refer electromagnetismÂ

Example 05:Â  Necta 1990 P1

(a)Â  Define the term “isoseismal line”.

(b)Â  Write short notes on each of the following regions of the atmosphere.

Â Â Â  (i)Â  Troposphere, (ii) Stratosphere, (iii) Exosphere

Example 06:Â  Necta 1990 P2

(a)Â Â  Explain clearly how P and S â€“ waves were used to ascertain that the outer core of the earth is in liquid form.

(b)Â Â  Giving reasons, discuss the temperature variation in atmosphere (above the earth’s surface).Â

(a)Â Â Â  P â€“ waves are longitudinal elastic, waves capable of passing through solids and liquids and S â€“ waves are traverse elastic waves capable of a travelling through solids only.

As both waves are projected towards the surface from interior core only the P â€“ waves are recorded.Â  This shows that the outer core is in liquid form.

(b)Â Â  From the ground level, the atmospheric temperature decreases steadily as altitude increases steadily as altitude increases up to the troposphere.Â Â  Thereafter the temperature increases with altitude up to the stratosphere.Â  The ozone of the stratosphere absorbs the incoming sun radiation hence the temperature increases.Â  In the mesosphere there is no ozone thus there is a decrease (cooling) with increasing altitude.Â  The heating effect of the earth ceases in the thermosphere so, the closer to the sun, the higher graph refer notes.

Example 07:Â  Necta 1991 P2

(a)Â Â Â Â  List down four physical changes that took place at a location just before onset of an earthquake at that particular location.

(b)Â Â Â Â  Give brief accounts of the processes that give rise to:

(i)Â  The earth’s magnetic field,

(ii)Â  Volcanic eruptions

(a)Â  Density of rocks, stresses faults and waves

(b)Â  (i)Â  Explain generation of the earth’s field in the atmosphere and the outer core.

(ii)Â Â Â Â Â Â Â Â Â Â Â Â  The seismic or earthquakes waves result from a fracture or sudden deformation of the earth’s crust.Â  Vast stresses do occur locally in the rocks being concentrated where the rocks are sliding over one another.Â  In regions where pressure is reduced, pockets of molten rock called magma are formed.Â  Once the rock has melted the pressure may force it into cracks and fissures in the surrounding solid rock.Â  This may emerge above the surface as a lava flow or volcano.

Example 08:Â  Necta 1992 P1

(a)Â  What do you understand by the term ionosphere?

(b)Â  Explain how short wave long distance transmission and reception of radio waves is more effective at night than it is during the day time.

(b)Â Â Â Â  In the day time, the base of the ionosphere (D-layer) is at lower heights where the high concentration of particles allows for ionization and recombination of ions by collision.Â  Because of this, radio waves are absorbed rather than reflected, so distance communication is poor.

During the night time, the D â€“ layer disappear, the base of the ionosphere is higher thus the recombination of ions is rare and so less absorption of waves occurs.Â  Obliquely transmitted waves therefore can be reflected for distant reception.Â

Example 09: Necta 1993 P2

(a)Â Â  What is the origin of the earth’s magnetic field?

(b)Â  The diagram below shows the structure of the Earth.Â  Name the parts indicated by the letter A to F.

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(b)Â  A represents Mohorovicic discontinuity

B represents Gutenberg discontinuity

C represents core

D represents Mantle

E represents Epicenter

F is not clear to interpret.Â

Example 10:Â  Necta 1994 P1

(a)Â  Define the terms:Â  angle of inclination (dip) and angle of declination (variation) as used in specifying the earth’s magnetic field at any point.

(b)The earth’s total resultant flux density BR in a certain country is found to be 5.0 x 10-5 T and the horizontal component is BH is 2.0 x 10-5 T.Â  Calculate ;

(i)Â Â Â  The vertical component, Bv, and

(ii) The angle of inclination in that country

Solution

(b)Â  (i)Â  The vertical component is given by

(ii)Â  Angle of inclination is given by

Example 11:Â  Necta 1994 P1

(a)Â  (i)Â  Name the lowest layer of the atmosphere and the lowest layer of the ionosphere.

Â Â Â  (ii)Â  State the importance of each of these layers.

(b)Â  What is the ozone layer?Â

(a)(i)Â  The lowest layer of the atmosphere is troposphere and the lowest layer of the ionosphere is called the D â€“ layer.

Â Â  (ii)Â  The t troposphere supports life

The D â€“ layer is important for communication purposes as it reflects radio waves.

(b)The ozone layer is within the stratosphere.Â  In the ozone layer molecular oxygen (O2) is dissociated into atomic oxygen (O) which is then reformed into ozone (O3)

The ozone so formed absorbs ultra violet radiation thus protecting plants and shielding people from skin cancer and eye cataracts.Â

Example 12:Â  Necta 1994 P2

(a)Â Â Â Â  Illustrate the component of the earth’s magnetic field at a given point P in the earth’s atmosphere by a suitable diagram.

(b)Â Â Â  Using a tangent galvanometer, explain how you could determine the earth’s magnetic field.

Example 13:Â  Necta 1995 P1

(a)Â  (i)Â  which region of the solid earth includes the e earth’s centre?

(ii)Â  On which region of the solid earth do the continent rests directly?

(iii)Â  Which region of the ionosphere has the highest electron density?

(b)Â  Briefly explain how earthquake can be detected

(a)Â  (i)Â  inner coreÂ  (ii)Â  crustÂ Â  (iii)Â  F â€“ region

(b)Â Â  Detection of earthquake is done by recording or measuring the seismic waves generated by the earthquakes.Â  These waves are recorded by instrument called seismograph.

Â Example 14:Â  Necta 1995 P2

(a)Â Â Â Â  Draw a well labeled diagram which shows the interior structure of the earth.Â  Indicate also which part of the interior are in solid form and which are in liquid form.

(b)Â Â Â  Name and distinguish the type of waves that are produced by an earthquake.

(c)Â Â Â Â  Briefly describe the three ways in which signal form ground based transmitter can reach the receiver.

(a)Â  There are four types of seismic waves:

Body waves â€“ divided into P and S â€“ waves

Surface waves â€“ divided into love and Rayleigh

(b)Â Â Â  A telecommunication problem.

Ground wave, sky wave and space waves

Example 15: Necta 1998 P1

Â  Â  Â  (a)Â  State any three magnetic components of the earth’s magnetic field

Â  Â  Â  Â (b)Â  The horizontal and vertical components of the earth’s magnetic field at a certain location are; 2.73 x 10-5 and 2.1 x 10-5T respectively.Â  Determine the earth’s magnetic field at
Â Â Â Â Â Â Â  the location and its angle of inclination
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Solution

(a)Â  Components of the earth magnetic field are:

Vertical component (which point vertically downward)

Horizontal component which comprise lf:

Â Â Â Â Â Â Â Â Â  Eastly component (towards geographic north pole)

Â Â Â Â Â Â Â Â  Northly component (towards magnetic north pole)

(b)Â

Example 16:Â  Necta 1998 P1 B

(a)Â  What is the origin of the earth’s magnetic field?

(b) The following diagram shows the main layers forming the interior of the earth name the layers indicated by letters A to G.

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(a)Â  Refer notes

(b)Â  A = Earth’s surface, B = Crust, C = Moho discontinuity, D = Gutenberg discontinuity, E = outer core, F = Mantle and G = inner core.

Â Example 17:Â  Necta 1998 Â B

(a)Â  Explain the following terms; Earthquake, Earthquake focus, Epicenter and body waves.

(b)Â  List down three (3) sources of earthquakes,

(c)Â Â  (i)Â  Define ionosphere

(ii)Â Â Â Â Â Â Â Â Â Â Â Â  Mention the ionosphere layers that exist during the day time

(iii)Â Â Â Â Â Â Â Â Â Â  Give the reason for better reception of radio waves for high frequency signal of night than during day time.

(d)Â  Explain briefly three different types of radio waves traveling from a transmitting station to a receiving antenna.

(a)Â  Refer notes

(b)Â  Refer notes

(c)Â Â  (i)Â  During the day time all the layers D,E,F1, and F2 â€“ layers exists.

Â Â Â Â Â Â  (ii) Refer Necta 1992 (b)

(d)Â  Ground (surface wave)

Â Â Â Â Â Â  Space wave

Â Â Â  Sky waves) (refer telecommunication notes)

Â Example 18:Â  nectar 2000 P1

(a)Â Â  With reference to an earthquake on a certain point of the earthÂ  explain the terms ‘focus’ and ‘Epicenter’

(b)Â  What is importance of the following layer of the atmosphere?

(i)Â  The lowest layer

(ii)Â  The ionosphere

(c)Â  (i)Â  Describe two ways by which seismic waves may be produced.

(ii) Describe briefly the meaning and application of “seismic prospecting”.

(a)Â  Refer notes

(b)Â  (i) Â Importance of troposphere is supports life on earth

Â Â Â Â  (ii)Â  Ionosphere enhances communication over long distances.

(c)Â Â  (i)Â  Describe any two causes of earth quake

(ii)Â Â Â Â Â Â Â Â Â Â Â Â  Seismic prospecting is an artificial production of seismic waves purposely for searching underground fuels and oils or gases

Â Example 19:Â  Necta 2001 P1

(a)Â Â Â Â Â  (i)Â  Define the terms “angle of declination” as used in the specification of the earth’s Â Â magnetic field at a point

(ii)Â Â Â The horizontal component of the earth’s magnetic field at a location was found to be 26.0 Â while the angle of inclination was Â  Find the magnitude of the field and the vertical component of the field at the location

(b)Â  (i)Â  Define an earthquake

Â Â Â Â  (ii)Â  Distinguish between P and S waves.Â  What factors influence their velocities?

(a)Â  (i)Â  Refer notes

Â Â Â Â  (ii)Â

(b)Â  The velocities of P and S waves are influenced by;

Â Â Â Â Â Â Â Â  Density, of the media

Â Â Â Â Â Â Â Â  Shear modulus, of the media, and

Â Â Â Â Â Â Â  Bulk modulus, B of the media.

Â Example 20:Â  Necta 2002 P1

(a)Â  (i)Â  What is the importance of ionosphere to mankind?

Â Â Â Â Â  (ii)Â  Explain why transmission of radio waves is better at night than at day time.

(b)Â  (i)Â  What is an earthquake?

Â Â Â Â Â  (ii)Â  Explain briefly any four (4) causes of earthquake

Â Example 21:Â  Necta 2003 P2

(a)Â  Explain the following:

Â Â Â  (i)Â  EarthquakeÂ Â  (ii) Earthquake focusÂ Â  (iii) The epicenter.

(b)Â  List down three sources of earthquake

(c)Â  (i)Â  Define the ionosphere

Â Â Â Â  (ii)Â  State the ionosphere layer that exists during day time.

(iii)Â Â  Give the reason for better waves reception for light frequencies signal at night than during the day time

Â Example 22:Â  Necta 2004 P1

(a)Â  (i)Â  Explain the terms epicenter and focus as applied to earthquake.

Â Â Â Â Â  (ii)Â  State any four (4) indications that may predict the occurrence of an earthquake.

Â Â Â Â  (iii) State and explain two variations of the earth magnetic field.

(iv)Â Â  State one necessary precaution to be taken to people living in a region with a high risk of occurrence of earthquakes.

(b)Â  Explain the following

(i)Â  Solar windÂ Â  (ii)Â  MagnetopauseÂ Â  (iii)Â  Ionosphere.

Â Example 23:Â  Necta 2005 P1

(a)Â  Define the following terms

Â Â Â  Â Â  (i)Â  Epicentral distance (ii) Body waveÂ Â  (iii) Seismograph

Â (b)Â  (i) explain the meaning of reflection seismology state its application

Â Â Â  Â Â  (ii)Â  Show how the magnetic field within the atmosphere is generated?

Â Â Â Â Â Â Â  (c) (i) Name the lowest layers of the atmosphere and the ionosphere

Â Â Â Â Â Â Â Â Â  Â  (ii)Â  State their importance

(a)Â  (i) Lowest layer of atmosphere is troposphere and that of the ionosphere is the D â€“ layer.

Â Example 24:Â  Necta 2006 P1

(a)Â  (i)Â  State two (2) ways by which seismic wave may be produced

Â Â Â Â Â  (ii)Â  What is seismic prospecting?

(b)Â  (i)Â  Discuss briefly the importance of the lowest layer of the atmosphere and the ionosphere.

(ii)Â Â Â Â  Sketch the temperature against altitude curve for the atmosphere indicating the important atmospheric layers.

(iii)The average velocity of P â€“ waves through the earth’s solid core is 8kms-1.Â  If the average density of the earth’s rock is 5.5 x 103kgm-3 find the average bulk modulus of the earth’s rock.

(a)Â  (i)Â  Causes of an earthquake

(b)Â  (ii)Â  using the formula

Â Example 25:Â  Necta 2007 P1

(a)Â  (i)Â  What are the differences between P and S waves?

(ii)Â Â Â  Explain how the two terms of waves (P and S) can be used in studying the internal structure of the earth.

(b)Â  Write short notes on the following terms in relation to the changes in the earth’s magnetic field; long term (secular) changes, short â€“ period (regular) changes, and short â€“ term (irregular) changes.

(c)Â Â Â Â Â  (i) What is geomagnetic micro pulsation?

Â  (ii)Â Â  Give a summary of location, constitution and practical uses of the stratosphere, ionosphere and mesosphere.

(c)Â  (i)Â  Geomagnetic micro pulsation are small rapid changes in the earth’s magnetic field.Â  They have periods between 0.2 second and 10 minutes and intensities less than 0.01% of the minimum field.

Â Example 26:Â  Necta 2008 P1

(a)Â  Define the following terms:

(i)Â  Earthquake (ii) atmosphere

(b)Â  Distinguish between body waves and surface waves that are produced by an earthquake.

(c)Â Â  (i)Â  Define the terms epicenter and focus as applied to earthquake.

Â Â Â Â Â Â  (ii)Â  Draw a well labeled diagram which shows the interior structure of the earth.

Â Example 27:Â  Necta 2009 P1

(a)Â  (i)Â  What is meant by the shadow zone?

Â  Â  Â  (ii)Â  Why does the shadow zone occur?

(b)Â  (i)Â  Name the lowest layer of the atmosphere and the lowest layer of the ionosphere.

Â Â Â Â Â  (ii) Â State the importance of each of these layers in b (i) above

(iii)Â Â Explain briefly the reason for better reception of radio waves for high frequency signals at night times than during day times.

(c) State the sources of heat energy in the interior of the earth.

Â Example 28:Â  Necta 2010 P1

(a)Â  (i)Â  Explain the terms:Â  earthquake, earthquake focus and epicenter.

(ii)Â  Describe clearly how P and S waves are used to ascertain that the outer core of the Earth is in liquid form.

(b)Â  (i)Â  Define the ionosphere and give one basic use of it.

Â Â Â Â  (ii)Â  Why is the ionosphere obstacle to radio astronomy?

Â Example 29:Â  Necta 2011 P1

(a)Â  (i)Â  Define the following terms:Â  Geophysics, Atmosphere and Epicenter

(ii)Â  Write down brief notes on the location, composition and importance of the following:

Troposphere, Stratosphere, Mesosphere and Thermosphere

(b)Â  (i) Draw sketch diagram showing the working part of a Seismometer.

Â Â Â Â Â  (ii)Â  Explain how temperature varies with both altitude and depth of the Earth.

Â Â Â Â  (iii)Â  Write down two factors that governs heat flow from the interior of the Earth.

Â Example 30:Â  Necta 2012 P1

(a)Â  (i)Â  Name three layers of the atmosphere

Â Â Â Â Â  (ii)Â  Describe any two major zones of the earth.

(b)Â  (i)Â  What are the factors that influence the velocities of P and S waves?

Â Â Â Â Â  (ii)Â  The P and S waves from an earthquake with a focus near the earth’s surface travel through the earth at nearly a constant speed of 8 km/s and 6 km/s respectively.Â  If there is no reflection and refraction of waves how long is the delay between the arrivals of successive waves at a seismic monitoring station at 900 in the latitude from the epicenter of the earthquake?

Solution

(a)Â  (ii)Â  any two of core, mantle, crust, hydrosphere, atmosphere

(b)Â  (i)Â  the density of rock, moduli of elasticity of rock material.

Â Â Â Â Â  (ii)Â  Illustration (R = earth radius)

 Â Â Â Â

###### edu.co.tz

Distance travelled by the waves (distance between focus and seismic station) is

Time taken by P â€“ waves to arrive at the station is

Time taken by the waves to arrive at the station is

The time interval between the arrival of the two waves is t = t2 â€“ t1 = 25.1 = 18.9 = 6.2 minutes.

Â Example 31:Â  Necta 2012 P1

(a)Â  (i) What do you understand by the word environmental physics?

Â Â Â Â Â  (ii)Â  Briefly explain three effects of seismic waves.

(b)Â  (i)Â  Mention three types of environmental pollution

(ii)Â Â Â Â  Explain on the following climatic factors which influence plant growth:Â  Temperature, Relative humidity and wind.

Â Example 32:Â  Necta 2013 P1

(a)Â Â Â Â Â Â  (i)Â  The main interior of the earth core is believed to be in molten form.Â  What seismic evidence supports this belief?

Â (ii)Â Â Â Â  Explain why the small ozone layer on the top of the stratosphere is crucial for human survival

(b)Â  Electrical properties of the atmosphere are significantly exhibited in the ionosphere.

Â (i)Â  What is the layer composed of and what you think is the origin of such constituents

(ii)Â Â Â  Mentioned two uses of the ionosphere

(c)Â  Briefly explain why long distance radio broadcasts make use of short wave

(a)Â Â Â  (i)Â  When P and S seismic waves are sent from one side of earth to the other, only P waves can be detected on the other side. The fact that S waves do not travel through the core provides evidence for the existence of a liquid core.

(ii)Â  Ozone absorbs harmful radiation from the sun. The Ozone projects plant and shield people from skin cancer and eye cataracts.

(b)Â Â  (i)Â  The layer is composed of free electrons and positive ions. The ionosphere is created by atoms absorbing UV radiation, gamma and x-rays.

(ii)Â  Uses of the ionosphere

Â Â  Ionosphere supports radio communication over long distances

Â Â Â  Particles in the ionosphere absorbs U.V radiation gamma and X-rays, thus protecting people from harmful effects of these radiations

(c)Â Â Â  Refer telecommunication notes.

Â Example 33:Â  Necta 2013 P1

(a)Â  Briefly explain on the following types of environmental pollution:

(i)Â  Thermal pollution

(ii)Â  Water pollution

(b)Â Â Â Â Â  Describe the soil temperature with regard to agriculture, physics which causes lower crop growth at a particular area

(b)Â Â Â Â Â  High soil temperature causes the crop roots to rot, this leads to insufficient water supply to plant leaves and hence lower the growth of crop.

Lower soil temperature inactivates soil organisms.Â  Decomposition of organic matter is lowered and hence the supply of nutrients to crop which in turn lead to lower crop growth.

TRY YOURSELF

(a)Â  (i)Â  What are auroras?

Â Â Â Â Â  (ii)Â  Define the homosphere

(b)Â  (i)Â  What are the factors which contribute toward volcanic eruptions?

Â Â Â Â Â  (ii)Â  What are the effects of volcanic eruptions?

Â Â Â Â Â  (iii)Â  What are lahars?

Lahars are rapidly flowing mixtures of rock debris and water that originate on the slopes of a volcano.Â  They are also referred to as volcanic mudflows or debris flow. Volcanic eruptions may directly trigger one of more lahars Â by quickly melting snow and on a volcano or eject water from a crater lake.Â  The form in a variety of at always including through intense rainfall on loose volcano rock deposits and as a consequence of debris of debris avalanches

Â ENVIRONMENTAL POLLUTION

Pollution is the addition of unwanted materials or pollutants into the environment.

Pollutant is any substance that does not belong in the natural system and disrupts the natural balance.

Type of Environmental pollution

(a)Â Â  Air pollution (atmospheric pollution)

(b)Â Â  Water pollution (hydrosphere pollution)

(c)Â Â  Land (soil) pollution

(d)Â Â  Noise pollution

(e)Â  Thermal pollution

Â ATMOSPHERIC (AIR) POLLUTION

AIR POLLUTION
This is a form of environmental pollution caused by the release of gaseous materials and dust particles in the atmosphere.Â  The main pollutants found in the air we breathe include, particulate matter, lead, ground-level ozone, heavy metals, sulphur dioxide, benzene, carbon monoxide and nitrogen dioxide

Causes of Air Pollution

(i)Â  Clearing (deforestation) and burning of vegetation.Â  This releases carbon dioxide in the atmosphere and dust particles which may be carried by wind on bare land.

(ii)Â Â  Burning of fuels:Â  This releases green house gases in the atmosphere.Â  Fuels are burnt in cars, power stations and industries.

(iii)Â Â  Construction activities, like road, building, etc construction, can add dust particles in the atmosphere.

(iv)Â Â  Automobile exhausts.Â  Car, trains, etc burns fuels as they move his releases pollutant gases in the atmosphere.

(v)Â Â  Smokes from industries also pollute the atmosphere.

(vi)Â  Agriculture activities.Â  The use of pesticide/insecticides pollutes the air.

(vii)Â  Mining activities

Natural causes:

(a)Â Â  Volcanic eruptions – release smoke and dust particles in the atmosphere

(b)Â  Wind storms â€“ carry land particles into the air

(c)Â Â  Temperature inversion â€“ the increase in temperature in the stratosphere causes high altitude particles to sink to the troposphere

WATER POLLUTION

Water Pollution is the degradation of water quality in a manner that disrupts/prevents its intended or original use.

Surface Water or Ground water may be polluted

Causes of water pollution

Â (i)Â Â Â  Disposal of untreated sewage (industrial or hospital, etc) into the water bodies.

Â (ii)Â Â Â  Wind may introduce dust particles into water from the land.

(iii)Â Â  Agriculture activities near water bodies.Â  Chemical used during farming may be taken to the water bodies by the rain water.

(iv)Â Â  Oil spilt.Â  The leakage of oil in under water oil pipe, leakage from boats, ships, etc pollutes the water.

(v)Â Â  Fishing by using chemicals (dynamite fishing).

(vi)Â Â  Volcanic activities along water bodies.

(vii)Â Â  Quarrying along the coast.

Â LAND (SOIL) POLLUTION

Soil pollution is defined as the build â€“ up in soils of persistent toxic compounds, chemicals, salts, radioactive materials, or disease causing agents which have adverse effects on plant growth and animal health.

A soil pollutant is any factor which deteriorates the quality, texture and mineral content of the soil or which disturbs the biological balance of the organisms in the soil.

Causes of soil pollution

(a)Â Â Â Â Â Â Â Â Â Â Â Â Â  Chemical from industries

(b)Â Â Â Â Â Â Â Â Â Â Â Â Â  Acid rain â€“ this increase soil acidity

(c)Â Â Â Â Â Â Â Â Â Â Â Â Â  Farming activities which make use of insecticides/pesticides

(d)Â Â  Mining activities â€“ increase rock sediment into the soil.

NOISE POLLUTION

Noise pollution is any disorganized loud sound.

Causes of noise pollution

(a)Â Â Â Â Â Â Â Â Â Â Â Â Â  Noise from factories and workshops

(b)Â Â Â Â Â Â Â Â Â Â Â Â Â  Thunderstorm explosion of bombs

(c)Â Â Â Â Â Â Â Â Â Â Â Â Â  Low level flying aircraft

(d)Â Â Â Â Â Â Â Â Â Â Â Â Â  Radio on large volumes

(e)Â Â Â Â Â Â Â Â Â Â Â Â Â  Slamming of doors

Â THERMAL POLLUTION

Thermal Pollution is a form of environmental pollution caused by the release of waste heat into water or air

Â Causes of Thermal Pollution

(a)Â Â Â Â Â Â Â Â Â Â Â Â Â  i. Hot gases released by industries and motor vehicles warm the environment.

Â ii. Hot wasteful liquid from industries pumped to a river, lake, or other waterway

Effects of thermal pollution

(a)Â  Heat introduced into water can make the water so hot that no living thing can survive in it

(b)Â  Hot gases introduced in the atmosphere leads to green house effects.

Â Solutions of thermal pollution

(a)One is a cooling pond into which heated waste water is released before it enters a natural waterway.Â  The cooling pond permits evaporation of some water, carrying heat into the air and thus releasing cooler water into the waterway

(b)The cooling tower method â€“ either wet or dry â€“ which also transfers heat to the air.Â  In both types, heated water is introduced into a tower through which air is blown, and some heat is passed to the air.

Â PARTICULATE MATTER IN THE ATMOSPHERE (AEROSOLS)

Particulate matter (aerosol) is the general term used for a mixture of fine solid particles and liquid droplets found in the air.

Haze aerosol is frequently encountered in optical studies and includes any airborne particles that affect visibility.

Classification of Particulate

Particulates matter are classified in accordance with its formation mechanisms

(i) Primary particlesÂ Â Â Â  (ii) Secondary particles

Â Primary particles are directly emitted into the atmosphere from their sources while secondary particles are formed after chemical transformation of their gaseous precursors. Chemical reactions transform primary pollutants (emitted by the sources) to secondary pollutants that are formed within the atmosphere.Â  Ozone, sulfate aerosols, nitrates, are examples of secondary pollutants.

Particulate matters in the atmosphere are categorized as:

(i)Â  Minerals, 72 â€“ 91%, e.g. soil particles, hematite, mica, and talc;

(ii) Combustion products, 1 â€“ 10%, e.g. coal and oil soot, fly ash, burned paper.

(iii) Biological materials 2 â€“ 10% e.g. pollen, spores, starch, plant tissues and diatoms

(iv) Miscellaneous matter, trace â€“ 8% e.g. salt, rubber, iron/steel, paint pigment and humus

Dust refers to a relatively course range of solid particles (diameter, d >1pm), produced by disintegration of minerals or from re-suspension by wind when sun blasting of soil particles may often causes comminuting.

Smokes and fumes are fine particles formed from the gas phase by condensation.Â  In the case of fume the particles are generally from 0.01 â€“ 1 pm diameter, and are often observed as agglomerates of smaller particles.Â  Suspended particulate matter < 15 pmÂ and diameter is usually defined as smoke.

Mists and fogs are liquid droplets Mists (d > 40 pm) and fogs (d = 5 â€“ 40 pm).

Advantages of particulate matter in the atmosphere

Â Aerosols acts as nuclei were water vapour collects during the formation of water droplets through condensation.

Disadvantages of particulate matter in the atmosphere

(a)Â  Cause global warming

(b)Â  Can block the atmosphere (impair visibility)

(c)Â  Once deposited on leaves they block stomata and hence no photosynthesis for plant

(d)Â  Changing the timing and location of traditional rainfall patterns

(e)Â  Can lead to development of heart and lung diseases.

TRANSPORT MECHANISMS OF ATMOSPHERIC POLLUTANT

The transport of pollutants by the wind

The three transport processes that influence the regional dispersion are;

Â  Â  Â  (a)Â  Wind speed (shear)

Â  Â  Â  (b)Â  Directional veer (change in direction fo wind), andÂ

Â  Â  Â  (c)Â  Eddy motion (eddy diffusion).

Wind shear:Â  The vertical gradient of wind speed (i.e. wind shear is responsible for lagging of low elevation pollutants behind those in the upper layers.

Directional veer:Â  The directional veer with height causes lateral displacement of a vertically uniform puff.

The eddy motion is the vertical transport of pollutants from region of high concentration to low concentration.Â  Eddy motions are due to random vertical and horizontal fluctuations caused by thermal and mechanical turbulence.

Â  Â  Both the transport speed and direction for an air parcel vary from day to day.

Stratosphere â€“ troposphere interchange

Temperature inversion at the tropopause causes an interchange of particulate matters between Stratospheres â€“ troposphere boundary.

EFFECTS OF POLLUTION ON VISIBILITY

Atmospheric pollution results into a reduction in visual range in the atmosphere.Â  The reduction is visual range caused by an increase in airborne particles that affects light scattering and attenuation involves both primary and secondary aerosols, and may be experienced in rural as well as urban area.

EFFECTS OF ATMOSPHERIC POLLUTION ON THE GLOBAL ALBEDO AND CLIMATE

Increases in particulate matter in the atmosphere may:

(a)Â  affect cloud droplet formation and precipitation,

(b)Â  Reduce the amount of solar radiation that reaches the ground

(c)Â  Reduce the cooling of the surface layer of the earth at night and influence the global albedo.

However, controversy still remains as to whether the presence of particulate material exerts a net warming or cooling effect to enhance or offset the global warming predicted from increases in CO2 and chlorofluoro methanes in the atmosphere.Â  In addition, considerable changes in global and surface albedo have been caused by deforestation, salinization, and desertification.

Global warming is the increase of the average temperatures near or on the surface of the earth as a result of greenhouse effect.

GLOBAL WARMING

Global warming is the increase of the average temperatures near or on the surface of the earth as a result of greenhouse effect.

Greenhouse effect

Greenhouse effect is the process in which the emission of radiation by the atmosphere warms the earth’s surface.

Greenhouse gases include carbon dioxide, methane, chlorofluorocarbons and dinitrogen oxide.

When heat from the sun reaches the earth’s surface in form of sunlight, some of it is absorbed by the earth.Â  The rest is radiated back to the atmosphere at a long wavelength than the incoming sunlight.Â  Some of these longer wavelengths are absorbed by the greenhouse gases in the atmosphere before they are lost out of space.Â  The greenhouse gases reflect the heat back to the earth and warm the environment.

Sources of greenhouse gases in the atmosphere

(a)Â  Carbon dioxide is added in the atmosphere by:

(i) Clearing and burning of vegetation

(ii) Burning of fossil fuels

(b)Â  Methane is added in the atmosphere by:

(i) Agricultural activities;

(ii) The mining of coal and oil

(c)Â  Dinitrogen oxide is added in the atmosphere by:

(i)Â  Combustion of fossil fuels in vehicles and power station

(ii)Â  Use of nitrogenous fertilizer, and

(iii)Â  The burning of vegetation and animal waste

(d)Â  Sources of chlorofluorocarbon include fridge, air conditioners and aerosols.

Effects of Global Warming

(a)Â Â  Increase in the temperature of the oceans,

(b)Â  Rise in sea levels,

(c)Â Â  Change in world’s climatic patterns,

(d)Â  Acidification of the oceans,

(e)Â Â  Extreme weather events like flood, droughts, heat waves, hurricanes and tornadoes

(f)Â Â Â  Higher or lower agriculture yields,

(g)Â Â  Melting of Arctic ice and snow caps.Â  This causes landslides, flash floods and glacial lake overflow,

(h)Â  Extinction of some animals and plant species,

(i)Â Â Â  Increase in the range of disease vectors (organisms that transmit disease).

Solution to Global Warming

(a)Â Â  Use of cleaner alternative sources of energy such as solar and wind,

(b)Â  Put in place energy conservation measures to reduce the use of fossil fuel,

(c)Â Â  Planting trees that would absorb carbon dioxide

(a)Â Â  Use of cleaner alternative sources of energy such as solar and wind,

NUCLEAR WASTE AND METHODS OF DISPOSAL

Nuclear wastes are the chemical products (solid, liquid and or gases) of nuclear reactions in the nuclear reactor.

For the purpose of disposal, radioactive waste is divided into the following categories:

(a)Â Â Â Â  High â€“ level waste (HLW):Â  spent fuel (SF) not destined for reprocessing; vitrified fission product solutions from reprocessing of spent fuel.

(b)Â Â Â  Alpha â€“ toxic waste (STW):Â  waste with a content of alpha â€“ emitters exceeding a value of 20,000 Becquerel’s per gram of conditioned waste.

(c)Â Â Â Â  Low â€“ and intermediate â€“ level (L/ILW): all other radioactive waste.

Nuclear Waste Disposal

(a)Â Â Â Â Â  Deep geological repository:Â  for spent fuel and vitrified fission product solution product solutions from reprocessing.Â  The products are buried deep into the earth.

(b)Â Â Â Â  Recycling of the nuclear waste.