# GP Magnetism

#### Which statements about magnetic field lines is not correct

Which one of the following statements about magnetic field lines is not correct?

1. They can emanate from a point
2. They do not cross each other
3. Field lines between two poles cannot be precisely straight lines at the ends
4. There are no filed lines within a bar magnet

#### What is the net force experienced by a bar magnet

What is the net force experienced by a bar magnet placed in a uniform magnetic field?

1. Zero
2. Depends upon length of the magnet
3. Never zero
4. Depends upon temperature

#### A current-carrying wire is known to produce magnetic lines of force

A current-carrying wire is known to produce magnetic lines of force around the conducting straight wire. The direction of the lines of force may be described by

1. left-hand thumb rule for up-current and right-hand thumb rule for down current
2. right-hand thumb rule for both up and down currents
3. right-hand thumb rule for up-current and left-hand thumb rule for down current
4. left-hand thumb rule for both up and down currents

#### A cyclotron accelerates particles of mass m and change q

A cyclotron accelerates particles of mass m and change q. The energy of particles emerging is proportional to

1. q/m2
2. q2/m
3. q2/m2
4. q

#### A force F, acting on an electric charge q, in presence of an electromagnetic field

A force F, acting on an electric charge q, in presence of an electromagnetic field, moves the charge parallel to the magnetic field with velocity v. Then F is equal to (where E and B are electric field and magnetic field respectively)

1. q(v x B)
2. q(v x E)
3. qB
4. qE

#### Which devices changes low voltage alternating current to high voltage

Which one of the following devices changes low voltage alternating current to high voltage alternating current and vice versa?

1. Generator
2. Motor
3. Transformer
4. Vibrator

#### At which place Earth’s magnetic field becomes horizontal

At which place Earth’s magnetic field becomes horizontal?

1. Magnetic meridian
2. Magnetic equator
3. Geographical pole
4. Tropic of Cancer

#### Step-up transformers are used for

Step-up transformers are used for

1. increasing electrical power
2. decreasing electrical power
3. decreasing voltage
4. increasing voltage

#### To convert an AC generator into DC generator

To convert an AC generator into DC generator

1. split-ring type commutator must be used
2. slip rings and brushes must be used
3. a stronger magnetic field has to be used
4. a rectangular wire loop has to be used

#### The strength of magnetic field inside a long current carrying straight solenoid is

The strength of magnetic field inside a long current carrying straight solenoid is

1. more at the ends than at the centre
2. minimum in the middle
3. same at all points
4. found to increase from one end to the other

#### A constant current flows in a horizontal wire in the plane of the paper

A constant current flows in a horizontal wire in the plane of the paper from east to west as shown in Figure. The direction of magnetic field at a point will be North to South 1. directly above the wire
2. directly below the wire
3. at a point located in the plane of the paper, on the north side of the wire
4. at a point located in the plane of the paper, on the south side of the wire

#### In the arrangement there are two coils wound on a non-conducting cylindrical rod

In the arrangement shown in Figure there are two coils wound on a non-conducting cylindrical rod. Initially the key is not inserted. Then the key is inserted and later removed. Then 1. the deflection in the galvanometer remains zero throughout
2. there is a momentary deflection in the galvanometer but it dies out shortly and there is no effect when the key is removed
3. there are momentary galvanometer deflections that die out shortly; the deflections are in the same direction
4. there are momentary galvanometer deflections that die out shortly; the deflections are in opposite directions

#### Commercial electric motors do not use

Commercial electric motors do not use

1. an electromagnet to rotate the armature
2. effectively large number of turns of conducting wire in the current carrying coil
3. a permanent magnet to rotate the armature
4. a soft iron core on which the coil is wound

#### A uniform magnetic field exists in the plane of paper pointing from left to right

A uniform magnetic field exists in the plane of paper pointing from left to right as shown in Figure. In the field an electron and a proton move as shown. The electron and the proton experience 1. forces both pointing into the plane of paper
2. forces both pointing out of the plane of paper
3. forces pointing into the plane of paper and out of the plane of paper, respectively
4. force pointing opposite and along the direction of the uniform magnetic field respectively

#### For a current in a long straight solenoid N- and S-poles are created at the two ends

For a current in a long straight solenoid N- and S-poles are created at the two ends. Among the following statements, the incorrect statement is

1. The field lines inside the solenoid are in the form of straight lines which indicates that the magnetic field is the same at all points inside the solenoid
2. The strong magnetic field produced inside the solenoid can be used to magnetise a piece of magnetic material like soft iron, when placed inside the coil
3. The pattern of the magnetic field associated with the solenoid is different from the pattern of the magnetic field around a bar magnet
4. The N- and S-poles exchange position when the direction of current through the solenoid is reversed

#### A circular loop placed in a plane perpendicular to the plane of paper

A circular loop placed in a plane perpendicular to the plane of paper carries a current when the key is ON. The current as seen from points A and B (in the plane of paper and on the axis of the coil) is anti clockwise and clockwise respectively. The magnetic field lines point from B to A. The N-pole of the resultant magnet is on the face close to 1. A
2. B
3. A if the current is small, and B if the current is large
4. B if the current is small and A if the current is large

#### If the key in the arrangement is taken out and magnetic field lines are drawn

If the key in the arrangement is taken out (the circuit is made open) and magnetic field lines are drawn over the horizontal plane ABCD, the lines are 1. concentric circles
2. elliptical in shape
3. straight lines parallel to each other
4. concentric circles near the point O but of elliptical shapes as we go away from it

#### North pole of a magnet can be identified by

North pole of a magnet can be identified by

1. Another magnet having its poles marked as North pole and South pole.
2. Another magnet no matter whether the poles are marked or not.
3. Using an iron bar.
4. Using iron filings.