CIE iGCSE Co-Ordinated Science P4.5.6 The transformer Exam Style Questions Paper 2
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
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
Ans :B
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: \(\frac{N_p}{N_s} = \frac{V_p}{V_s}\).
Question
Electrical energy from a power station is transmitted over a large distance. A 100% efficient transformer is used near to the power station. This transformer reduces the amount of energy that is wasted thermally in the transmission cables.
How does the transformer reduce the amount of energy that is wasted?
A. It decreases the power transmitted so the current and the voltage are both larger.
B. It decreases the power transmitted so the current and the voltage are both smaller.
C. It increases the current so the voltage is smaller.
D. It increases the voltage so the current is smaller.
▶️Answer/Explanation
Answer: D
Explanation: Transformers increase the voltage for transmission, which reduces the current. Since power loss in transmission cables is proportional to the square of the current, reducing the current minimizes energy loss.