1.

(a) the diagram shows a simple step-up transformer. it is designed to light a 6 v lamp using a 1.5 v power supply.

(i)

how can you tell from the diagram that this is a step-up transformer? ........................................................................................................................... (1)

(ii)

which material is used to make the core of a transformer? ........................................................................................................................... (1)

(iii)

state two ways in which the design of the transformer could be changed to reduce the brightness of the lamp. 1 ........................................................................................................................ ........................................................................................................................... 2 ........................................................................................................................ ........................................................................................................................... (2)

(b)

chris investigates three different transformers. for each transformer chris changes the potential difference across the primary (input) coil and measures the potential difference across the secondary (output) coil. the results for each transformer are given in the graph.6 .0 5 .0 P o te n tia l d if f e r e n c e 4 .0 a c ro s s th e s e c o n d a r y 3 .0 (o u tp u t) c o il in v o lts 2 .0 1 .0 0 .0 0 .0 0 .5 1 .0 1 .5 2 .0 2 .5 3 .0 P o te n tia l d iffe re n c e a c ro s s th e p rim a ry (in p u t) c o il in v o lts J K

L

which of the transformers, j, k or l, is working as a step-down transformer? ..................................................................................................................................... give a reason for your answer. .....................................................................................................................................cheam high school 1

..................................................................................................................................... (2) (c) the diagram shows how the national grid transmits electrical energy over long distances.

(i)

why do the power stations generate a.c. and not d.c? ........................................................................................................................... ........................................................................................................................... (1)

(ii)

state the purpose of transformer a and explain why it is an essential part of the national grid system. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (3) (total 10 marks)

2.

a transformer is used to reduce the 230 v a.c. mains to the 12 v supply required for the lighting system. the transformer has 1150 turns on its primary coil. (i) write down the equation which links the number of turns of each transformer coil to the voltage across each transformer coil. .................................................................................................................................... .................................................................................................................................... (1) (ii) calculate the number of turns on the secondary coil of the transformer. show clearly how you work out your answer. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... number of turns on the secondary coil = ......................... (2) (total 3 marks)