Magnetic Fields

In the diagram four long wires are

placed at the corner of a square and

carry equal currents. The direction

of the current in wires P and R is

into the plane of the paper and in

wires Q and S is out of the plane of

the paper.

Which labeled arrow correctly shows

the direction of the resultant force

on wire Q?

• Arrow A

• Arrow B

• Arrow C

• Arrow D

Jorge builds a simple electric motor

but makes a mistake. He forgets to

include the commutator and brushes

and connects the coil directly to the

power supply. The setup

is

represented in the diagram below

(only one turn of the coil is shown).

With the coil in the position shown,

when the switch S is closed the coil

will…

• rotate normally – but the wires

  would tangle.

• stop after half a revolution.

• stop after a quarter of a

  revolution.

• not move.

A strip of aluminium foil is held

between the poles of a strong

magnet, as shown below.

When a current is passed through

the aluminium foil in the direction

shown, the foil is deflected. In which

direction is this deflection?

• Vertically downwards

• Vertically upwards

• Towards the North pole of the

  magnet

• Towards the South pole of the

  magnet

The diagram shows a coil of wire

that can rotate between the poles of

a magnet about the axis XY.

A current is passed through the coil

by means of a commutator

connected to the ends of the coil.

What is the position of the coil in

the magnetic field so that its turning

effect is a maximum?

• Parallel to

  direction of field

• Normal to

  direction of field

A current-carrying solenoid is

placed with its axis pointing eastwest

as shown below. A small

compass is situated near one end of

the solenoid.

The axis of the needle of the

compass is approximately 45

o

to the

axis of the solenoid. The current in

the solenoid is then doubled. Which

of the following diagrams best

shows the new position of the

compass needle?

• 
• 
• 
• 

The diagram below shows two long

parallel wires, 1.0 m apart, on the

plane of the page. Each wire carries

a current I in the same direction.

Point P is on the plane of the page

midway between the two wires. The

magnitude of the magnetic field

strength at point P due to wire 1

alone is B0. The magnitude of the magnetic field strength at point P

due to both wires is

• 0.

• ½ B0 .

• B0.

• 2 B0 .