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CIE iGCSE Co-Ordinated Science P4.5.6 The transformer Exam Style Questions Paper 2

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Question

The output from the generator in a power station is connected to a transformer before electricity is sent along a transmission cable.

What is a reason for using this transformer?

A. to decrease the voltage and decrease the current
B. to decrease the voltage and increase the current
C. to increase the voltage and decrease the current
D. to increase the voltage and increase the current

▶️ Answer/Explanation
A step-up transformer increases voltage and decreases current. Power losses in cables are given by \(P = I^2R\); lowering current reduces energy loss, making transmission more efficient.
✅ Answer: (C)

Question

When electricity is generated in a power station, a step-up transformer is used before it is transmitted around the country.

Which statement explains why a step-up transformer is used?

A. The current decreases, the voltage increases so more energy is transferred by heating in the transmission cables.
B. The current increases, the voltage decreases so less energy is transferred by heating in the transmission cables.
C. The voltage decreases, the current increases so more energy is transferred by heating in the transmission cables.
D. The voltage increases, the current decreases so less energy is transferred by heating in the transmission cables.

▶️ Answer/Explanation
A step-up transformer increases voltage and decreases current (for the same power: \(P = IV\)). Power loss in transmission cables is given by \(P_{\text{loss}} = I^2R\). With lower current, the power loss due to heating is reduced, making transmission more efficient.
✅ Answer: (D)

Question

A transformer increases the voltage from a power station in order to transfer electricity along transmission cables.

How does increasing the voltage affect the current in the cables and how does it affect the efficiency of energy transfer?

▶️ Answer/Explanation
Since power equals voltage multiplied by current, increasing voltage for the same transmitted power means the current must decrease.
Energy lost as heat in the cables depends on current squared multiplied by resistance, so a lower current greatly reduces these losses.
Reducing energy losses in the cables increases the overall efficiency of energy transfer.
✅ Answer: (B)

Question

A 100% efficient step-down transformer has 120 turns on its primary coil and 10 turns on its

secondary coil.

A 240V supply provides 48W of power to the primary coil.
What is the current in the secondary coil?

(A) 0.017A           (B) 0.2A               (C) 2.4A               (D) 20A

▶️Answer/Explanation

Ans : C

Question 

The primary coil of a 100% efficient transformer has \( N_p \) turns and the secondary coil has \( N_s \) turns. The voltage supplied to the primary coil is \( V_p \) and the voltage induced across the secondary coil is \( V_s \). Which equation relates these terms?

A. \(\frac{N_p}{N_s} = \frac{V_p}{V_s}\)
B. \(\frac{N_p}{N_s} = \frac{V_s}{V_p}\)
C. \(N_p \times N_s = V_p \times V_s\)
D. \(N_p \times N_s \times V_p = V_s\)

▶️Answer/Explanation

Answer: A

Explanation: For a transformer, the ratio of the number of turns in the primary coil to the number of turns in the secondary coil is equal to the ratio of the primary voltage to the secondary voltage: \(\frac{N_p}{N_s} = \frac{V_p}{V_s}\).

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