Electromagnetic Effects (CIE IGCSE Physics: Co-ordinated Sciences (Double Award))

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Fig. 10.1 is a simplified top view of a flat coil. There is an alternating current (a.c.) in the coil.

Describe the magnetic effect of this alternating current.

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Fig. 10.2 shows a pan placed above the coil. The base of the pan is made of steel.

State what quantity is induced in the base of the pan.

The pan contains water.

State and explain the effect of the quantity induced in part (b) on the temperature of the water in the pan.

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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.

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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.

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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.

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

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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.

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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.

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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.

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There are 560 turns on the primary coil and 910 turns on the secondary coil of the transformer. The voltage between the two terminals of the secondary coil is 78 V.

Calculate the voltage supplied by the a.c. generator.

 generator voltage = ............................................................

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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.

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A teacher demonstrates electromagnetic induction using the apparatus shown in Fig.10.1.

The teacher pulls the magnet down until one end is inside the coil. The teacher then releases the magnet. The magnet moves up and down repeatedly. As it moves, one end of the magnet enters and leaves the coil.

 
Describe and explain the readings on the centre-zero millivoltmeter as the magnet enters and leaves the coil.

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Fig.10.2 shows a system for transmitting electricity from a power station.

State the name of the device used in X and the name of the device used in Y.

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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.

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Fig. 10.2 shows a transformer.

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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.

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

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

Complete Table 9.1 to give the turning effect for the changes made to the arrangement shown in Fig. 9.1.

Choose your answers from the box.

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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.

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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.

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