Electromagnetic Effects (CIE IGCSE Physics)

A student is experimenting with electromagnetic effects.

Describe an experiment, using any standard laboratory equipment, to demonstrate electromagnetic induction. You may draw a diagram.

Fig. 11.1 shows a transformer connected to an input voltage of 12 V a.c.

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Fig. 10.1 shows a straight wire AB placed in the magnetic field between the poles of a magnet.

 
The ends of AB are connected to a galvanometer.

When AB is moved vertically, the needle of the galvanometer shows a deflection.

 
State three factors that affect the size of the deflection.

Extended

Fig. 10.2 shows a transformer.

Extended

A student makes a transformer that uses an alternating current (a.c.) supply with an electromotive force (e.m.f.) of 12.0 V to induce an output potential difference (p.d.) of 2.0 V.

 
The student is provided with two lengths of insulated wire and the U-shaped piece of iron shown in Fig. 7.1.

Another transformer is used in a school laboratory to step down a mains supply with a p.d. of 110 V to 12 V. This transformer is mounted in a metal case.

 
State and explain an essential safety feature required for this arrangement.

Fig. 11.1 shows a vertical conductor passing through a horizontal piece of card.

Describe an experiment to show that a force acts on a current-carrying conductor in a magnetic field. Show how to arrange the equipment. Include a diagram in your answer.

Extended

A student wants to demagnetise a permanent bar magnet. She suggests these steps:

1. Place the magnet in a long coil.
2. Switch on a large alternating current in the coil.
3. Switch off the current.
4. Remove the bar from the coil.

State and explain whether the steps will always be able to demagnetise the magnet.

Extended

(i)

Fig. 9.1 shows a coil supplied with current using a split-ring commutator.

 

Extended

Explain why the voltage of the supply to the primary coil of a transformer must be alternating.

Extended

Fig. 10.1 shows a transformer.

There are 8000 turns in the primary coil of the transformer. The primary coil is connected to a 240 V mains supply. A 6.0 V lamp connected to the secondary coil operates at full brightness.

Fig. 9.1 shows a coil ABCD with two turns. The coil is in a magnetic field.

When there is a current in the coil, the coil experiences a turning effect.

Extended

Fig. 9.2 shows a magnet held just below a vertical coil connected to a galvanometer.

The magnet is released.

Fig. 11.1 shows in each of the diagrams a current-carrying conductor and a magnetic field pattern.

State the diagram which correctly shows the magnetic field around a current-carrying conductor.

Fig. 11.2 shows three pieces of equipment.

Extended

A student connects a lamp and centre-zero galvanometer in series with a generator, as shown in Fig. 11.3.

 

The student observes the galvanometer needle moving from side-to-side repeatedly. Explain why the needle moves in this way.

Fig. 9.1 shows a simple direct current (d.c.) electric motor. The coil rotates about the axis when there is a current in the coil. The coil is connected to the rest of the circuit by the brushes.

State any difference each of the following changes makes to the rotation of the coil in Fig. 9.1:

(i)

changing the polarity of the power supply to that shown in Fig. 9.2

 

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(ii)

changing the coil to the new coil shown in Fig. 9.3

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A student makes an electromagnet. He places an iron rod inside a coil of wire and connects
the coil to a d.c. power supply, as shown in Fig. 9.2.

A student has a model electric railway. The model railway uses a step-down transformer.

 
The input voltage is 230 V. The transformer has 1710 turns on the input coil and 90 turns on the output coil.

 
Calculate the output voltage of the transformer.

A step-up transformer is used to increase voltage.

Step-up transformers and step-down transformers have different coil arrangements.

 
Describe the differences in the coil arrangement for the two types of transformer.

Explain the advantage of transmitting electricity at high voltages, rather than at low voltages.

A transformer consists of two coils of wire wound on a metal core. Fig. 10.1 represents the transformer.

State the name of the metal from which the core is made.

Extended

The primary coil of the transformer is connected to the output voltage of an a.c. generator which supplies an alternating current.

Transformers are used to increase the voltage when electrical energy is transmitted in cables across long distances.

 
Explain why power losses in the cables are lower when the voltage is high.