During a field survey, students use the circuit in Fig. 1 to identify a buried metal cap. A search coil is connected to a sensitive meter. The coil is moved...
Question 1 Report
During a field survey, students use the circuit in Fig. 1 to identify a buried metal cap. A search coil is connected to a sensitive meter. The coil is moved steadily over the ground. The meter needle deflects only as the coil passes the cap.
(a) What observation shows that a potential difference has been induced? [1]
(b) Which action produces no meter deflection? [1]
(c) Give one way to make the induced potential difference larger. [1]
(d) Describe why the meter returns to zero after the coil has passed the cap. [2]
Two students build the alarm circuit in Fig. 1 for a greenhouse door. A reed switch is fixed to the frame and a magnet is fixed to the door. The buzzer sounds only when the door is open. The cell provides energy to the circuit.
(a) Which component changes electrical energy into sound energy? [1]
(b) What happens to the reed switch when the magnet is close to it? [1]
(c) Give one reason this circuit is useful for an alarm. [1]
(d) Draw the circuit symbol for a cell. [1]
Answer Details
Buried metal cap circuit
- The observation is that the meter needle deflects. A deflection shows that current is flowing, so an induced potential difference has been produced. [1]
- Holding the coil still produces no deflection. Induction requires a changing magnetic field through the coil; a stationary coil has no changing flux. [1]
- Move the coil faster, or use a coil with more turns. Either change increases the induced potential difference. [1]
- After the coil has passed the cap, the magnetic field through it stops changing. Therefore, no potential difference or current is induced, and the meter returns to zero. [2]
Greenhouse door alarm
- The buzzer changes electrical energy into sound energy. [1]
- When the magnet is close, the reed switch closes and completes the circuit. [1]
- The circuit detects that the door has moved/opened and gives a sound warning, so it is useful as an alarm. [1]
- A cell is represented by two parallel lines of unequal length:
The longer line is the positive terminal. [1]
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