Magnetic Effect of a Current and the d.c. Motor

Explain why the coil turns in the direction shown.

______

Explain why this happens.

______

Suggest one other way to increase the turning effect of the motor.

______

On Fig. 7.1, mark with an arrow the direction of the current in the copper wire.

Explain why the copper wire moves along the copper rods.

Name two different devices that use this effect.

1. ______
2. ______

In the table, mark one tick (✓) in each column to indicate the force on PQ and the force on QR.

The battery in the circuit in Fig. 7.1 is reversed.

State and explain the effect of this on PQ and QR.

The variable resistor is adjusted and the current in the circuit decreases.

Suggest one effect of decreasing the current.

A wire carrying a current in a magnetic field experiences a force due to the current. On Fig. 8.1, insert the words current, field and force in the boxes to show the relative directions of the current, the magnetic field and the force.

Calculate the total moment caused by these forces.

moment = ______

The moment is increased by using a stronger magnetic field.

State two other ways to increase the moment.

1. ______
2. ______

aluminium,

______

iron,

______

steel.

______

On Fig. 6.1, draw arrows to show the directions of the forces.

In order for the coil to rotate continuously, a split-ring commutator is connected between the battery and the coil.

Explain how the split-ring commutator enables the coil to rotate continuously. Include a diagram in your answer.

Fig. 7.1 shows a solenoid made from wire wound around a plastic cylinder.

A current in the solenoid produces a magnetic field.

On Fig. 7.1, draw the pattern of the magnetic field lines inside and outside the cylinder.

On Fig. 7.2, draw the path followed by one of the beta-particles in the shaded region.

The direction of the current in the solenoid is reversed. State what happens to the path of the beta-particle.

Explain why there is a force on side AB.

Determine the direction of the current in AB and state how the direction is deduced.

State the name of the device that connects the coil of a d.c. motor to the electricity supply.

State one change to the arrangement in Fig. 7.1 that produces a greater turning effect in coil ABCD.

When the current is greater than $10\ \text{A}$, the circuit-breaker stops the current. Explain what happens in the circuit-breaker when this occurs.

State and explain how the electromagnet can be altered so that the circuit-breaker stops the current at less than $10\ \text{A}$.

State what happens to the motor if a stronger magnet is used.

On Fig. 6.1 mark and label:

• the direction of the current in the coil
• the direction of the magnetic field.

Explain why the coil turns.

The currents in the two wires cause the wires to repel each other.

Explain how the current in one wire causes a force on the other wire.