Earth's Magnetic Field

Q. Why like poles repel each other and unlike poles attract each other?

Q.

How is a compass used to find directions? [5 MARKS]

Q. Why unlike poles attract each other?

Q. The needle of the compass shows north in the direction in which the of earth's magnetic field lies.

1. south pole
2. north pole
3. center

Q.

State true or false. The magnetic north and south poles of the earth are different from its geographical north and south poles.

1. True

2. False

Q. The earth itself acts as a huge

1. disc magnet
2. horse shoe magnet
3. bar magnet

Q. Four plotting compasses are placed near a bar magnet. One compass appears like this:


What is a possible position for the compass? (Ignore any effects of the Earth’s magnetic field.)

Q.

Lines of force due to earths horizontal magnetic field are

1. parallel and straight

2. concentric circles

3. elliptical

4. curved lines

Q. Are there poles in a circular magnet, are there poles on earth ?

Q.

The end of a freely suspended magnet that points to the magnetic north of earth is ___________.

Q.

How is the magnetism of help in navigation?

Q. The magnetic field can have the only ____ direction at a particular point.

1. 1
2. 4
3. 0
4. 2

Q.

Earth itself acts like a giant magnet.

1. True
2. False

Q.

Why are artificial magnets preferred to natural magnets?

Q. Assertion :When a bar magnet is freely suspended, it points in the north-south direction. Reason: The earth behaves as a magnet with the magnetic field pointing approximately from the geographical south to north.

1. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
2. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
3. Assertion is correct but Reason is incorrect
4. Both Assertion and Reason are incorrect

Q.

In which direction does a compass needle lie when placed away from a magnet?

Q. A compass works due to the effect of earth.

1. heating
2. magnetic
3. conducting
4. electrical

Q.

A compass is generally used to indicate _________.

1. speed

2. distance

3. time

4. direction

Q.

Horizontal component of earths magnetic field at a place is √ 3 times the vertical component. What is the value of angle of dip at this place ?

Q.

A freely suspended magnet always points in the _______ direction.

1. North-west

2. South-east

3. North-east

4. North-south

Q. The shape of the earth's magnetic field resembles that of an imaginary

1. solenoid
2. U-shaped magnet
3. current-carrying circular loop
4. bar magnet

Q. When a Magnetic needle is suspended freely, it always aligns itself in the direction of magnetic north and south pole of the earth, the north pole of the needle gets attracted towards the magnetic south pole of the earth and the south gets repelled equally away from it. So two equal and opposite forces acting on the needle should cancel each other which does not happen because the:

1. Force of attraction and repulsion are equal but not exactly in opposite direction
2. Force of attraction and repulsion are not equal and not in opposite direction
3. Force of attraction and repulsion are exactly equal and opposite in direction
4. Force of attraction and repulsion are not exactly equal even though in opposite direction

Q. The magnetic field of earth is due to :

1. Magnetic dipole buried at the centre of the earth
2. Interaction of gamma rays with the crust of the earth.
3. Motion and distribution of some material in and outside the earth.
4. Induction effect of the sun.

Q.

The power of attraction of a _____ magnet is twice as compared to similar bar magnet.

Q. The earth itself acts as a huge:

1. disc magnet
2. ring magnet
3. horsh shoe magnet
4. bar magnet

Q. The north pole of earth's magnet is near __________.

1. geographic north
2. the centre of earth
3. geographic south
4. Both (A) and (C)

Q. Answer the following questions:
(a) The earth's magnetic field varies from point to point in space. Does it also change with time? If so, on what time scale does it change appreciably?
(b) The earth's core is known to contain iron. Yet geologists do not regard this as a source of the earth's magnetism.Why?
(c) The charged currents in the outer conducting regions of the earth's core are thought to be responsible for earth's magnetism. What might be the 'battery' (i.e., the source of energy) to sustain these currents?
(d) The earth may have even reversed the direction of its field several times during its history of 4 to 5 billion years. How can geologists know about the earth's field in such distant past?
(e) The earth's field departs from its dipole shape substantially at large distances (greater than about 30, 000 km). What agencies may be responsible for this distortion?
(f) Interstellar space has an extremely weak magnetic field of the order of ${10}^{-12}T$. Can such a weak field be of any significant consequence? Explain.
[Note: Exercise is meant mainly to arouse your curiosity. Answers to some questions above are tentative or unknown. Brief answers wherever possible are given at the end. For details, you should consult a good text on geomagnetism.]

Q. A magnet is placed earth's magnetic field with south pole of the magnet pointing north. At the neutral point :

1. The earth's magnetic field is zero
2. The fields of the magnet and the earth are equal and in opposite direction.
3. The magnet's magnetic field is zero.
4. The net magnetic field is zero.

Q. Even though earth is a giant magnet, all the iron does not stick to it at north and south pole because

1. Iron is embedded in between rocks
2. Force of earth's magnetism is weak
3. Much iron is scattered away from the poles
4. Very less iron is present near the magnetic poles of earth

Q. As used in line 26127, "take the slightest interest in" most nearly means ______

1. accept responsibility for.
2. pay no attention to.
3. have curiosity about.
4. possess little regard for.