Force on Current Carrying Conductor in a Magnetic Field

A wire passes between the poles of a horseshoe magnet. There is a current in the wire in the direction shown, and this causes a force to act on the wire.

Three other arrangements, $\mathrm{P}, \mathrm{Q}$ and $\mathrm{R}$, of the wire and magnet are set up as shown below. Which arrangement or arrangements will cause a force in the same direction as the original arrangement? 

(You may choose more than 1 answer.)

The diagram shows a wire in the magnetic field between two poles of a magnet.

The current in the wire repeatedly changes between a constant value in one direction and a constant value in the opposite direction. This is shown on the graph.

What is the effect on the wire?

A toy railway engine is driven around a track by a d.c. electric motor.
How can the speed of the motor be increased?

The diagram shows a simple d.c. electric motor which is rotating.
Which change will make the motor rotate more quickly?

A metal rod $P Q$ rests on two horizontal metal wires that are attached to a battery. The rod lies between the poles of a magnet.

When the switch is closed, the rod moves to the right.
What could be changed so that the rod moves to the left?

The diagram shows a thin copper wire in a magnetic field. The current in the wire is from right to left. This causes an upward force on the wire.

The direction of the current and the direction of the magnetic field are both reversed.
In which direction does the force act on the wire, after these changes are made?

The diagram shows a flat, rectangular coil placed between the poles of a magnet.

There is a current in the coil that makes it turn in the direction shown in the diagram.
Which change would make the coil turn in the opposite direction?

The diagram shows a coil of wire between the poles of a magnet.

The coil consists of 20 turns of insulated wire.
The coil is connected to a variable resistor and a power supply.
How can the turning effect on the coil be increased?

The diagram shows a current-carrying conductor in a magnetic field.

Which arrow shows the direction of the force acting on the conductor?

Which device uses a split-ring commutator?

A simple d.c. electric motor is fitted with a coil that rotates in a magnetic field. A commutator connects the power supply to the coil.
What is the purpose of the commutator?

The diagram shows a shaded area where the direction of a magnetic field is into the page.

A beam of $\beta$-particles enters the field as shown.
In which direction is the beam of $\beta$-particles deflected as they enter the magnetic field?

A current-carrying coil in a magnetic field experiences a turning effect.

How can the turning effect be increased?

A current-carrying wire $X Y$ lies in the magnetic field between the two poles of a $U$-shaped electromagnet. A force acts on the wire $X Y$ because of the magnetic field.

Each of the following actions is carried out separately.

• The current in the wire $X Y$ is reversed.
• The magnetic field is reversed.
• Both the current in the wire $X Y$ and the magnetic field are reversed at the same time.

How many of these actions cause the direction of the force on the wire $X Y$ to be reversed?