Home / iGCSE Physics (0625) 4.5.6 The transformer Paper 4-2023,2024&2025

iGCSE Physics (0625) 4.5.6 The transformer Paper 4-2023,2024&2025

Question

A 240 V a.c. mains supply is connected to the primary coil of the transformer shown in

Fig. 10.1. A lamp that gives full brightness with a 6 V supply is connected to the secondary coil.

(a) Name a suitable material from which the coils may be made.

…………………………………………………………………………………………………………………….. [1]

(b) State the name given to the part of the transformer that is made of soft iron

(see Fig. 10.1).

…………………………………………………………………………………………………………………….. [1]

(c) Calculate the number of turns of wire in the secondary coil that will enable the lamp to

light at full brightness.

number of turns =…………………………….. [3]

(d) State what would happen to the lamp if the number of turns in the secondary coil was

(i) much less than that calculated in (c),

……………………………………………………………………………………………………………… [1]

(ii) much more than that calculated in (c).

……………………………………………………………………………………………………………… [1]

[Total: 7]

Answer/Explanation

Ans: (a) copper 

(b) core  (c) N_p / N_s = V_p / V_s in any form  8000/N_s = 240 / 6 OR 240 = 6 OR N_s = 6  8000 Ns 8000 240
200 

(d) (i) lamp less bright/less than full brightness/wouldn’t light  (up properly)/ has less energy

(ii) lamp blows/bursts OR lamp too bright OR lamp  overheats/burns out OR much brighter/has more energy

Question

 A radio is connected to the mains supply using a step-down transformer.

   (a) Draw a labelled diagram of the structure of a basic step-down transformer. [3]

   (b) Explain the operation of a basic transformer. [3]

   (c) The voltage of the mains supply is 230V. The output voltage of the transformer is 6.0V.

Calculate the value of the turns ratio \(\left ( \frac{N_{s}}{N_{p}} \right )\). Give your answer to two significant figures.

value of turns ratio =  [2] [Total: 8]

Answer/Explanation

Ans:

(a) Labelled diagram showing

  • labelled Iron (core)
  • two coils, labelled primary and secondary, (around core and connected to separate circuits)
  • Fewer turns on labelled secondary coil

(b) (Primary voltage causes) an alternating current in primary coil 
           produces a changing magnetic field 
           (changing) field induces pd / e.m.f. (in secondary coil)

(c) 0.026
         (Ns / Np =) Vs / Vp in any form

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