Magnetic Effects of Electric Current

Choose the incorrect statement from the following regarding magnetic lines of field

• The direction of magnetic field at a point is taken to be the direction in which the north pole of a magnetic compass needle points

• Magnetic field lines are closed curves

• If magnetic field lines parallel and equidistant, they represent zero field strength

• Relative strength of magnetic field is shown by the degree of closeness of the field lines

If the key in the arrangement (Fig.) is taken out (the circuit is made open) and magnetic field lines are drawn over the horizontal plane ABCD, the lines are

• concentric circles

• elliptical in shape

• straight lines parallel to each other

• concentric circles near the point O but of elliptical shapes as we go away from it

A constant current flows in a horizontal wire in the plane of the paper from east to west as shown in Fig. The direction of magnetic field at a point will be North to South.

• directly above the wire

• directly below the wire

• at a point located in the plane of the paper, on the north side of the wire

• at a point located in the plane of the paper, on the south side of the wire

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

• A

• B

• A if the current is small, and B if the current is large

• B if the current is small, and A if the current is large

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

• more at the ends than at the centre

• minimum in the middle

• same at all points

• found to increase from one end to the other

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:

• 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

• 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

• The pattern of the magnetic field associated with the solenoid is different from the pattern of the magnetic field around a bar magnet

• The N- and S-poles exchange position when the direction of current through the solenoid is reversed

Magnetic fields do not interact with

• electric charges at rest

• electric charges in motion

• permanent magnets at rest

• permanent magnets in motion.

A positive charge projected towards east is deflected towards north by a magnetic field. The magnetic field is directed

• towards west

• towards south

• upward

• downward

The force on a charged particle moving in a magnetic field is maximum when the angle between direction of motion and field is

• zero

• 90⁰

• 180⁰

• 45⁰

A uniform magnetic field exists in the plane of paper pointing from left to right as shown in Fig. In the field an electron and a proton move as shown. The electron and the proton experience

• forces both pointing into the plane of paper

• forces both pointing out of the plane of paper

• forces pointing into the plane of paper and out of the plane of paper, respectively

• force pointing opposite and along the direction of the uniform magnetic field respectively