The diagram shows an electrician using a solenoid probe to locate an iron inspection cap below a concrete floor. The probe contains a coil of wire wound aro...
Question 1 Report
The diagram shows an electrician using a solenoid probe to locate an iron inspection cap below a concrete floor. The probe contains a coil of wire wound around a soft iron core. It is connected to a battery, switch and ammeter. The electrician moves the probe slowly over the floor and records a larger current change when it is above the cap.
(a) State the purpose of the soft iron core in the solenoid. [3]
(b) Explain why the probe gives a larger response above the iron cap than above concrete. [4]
(c) Describe two changes that would make the electromagnet in the probe stronger. [4]
(d) When the switch is opened, explain why the probe can be moved safely without attracting nearby iron screws. [4]
Answer Details
(a) Current in the coil magnetises the soft iron core. The core concentrates the magnetic field and therefore makes the electromagnet stronger. [3]
(b) Iron can be magnetised, whereas concrete is not magnetic in this way. Above the cap, the solenoid field magnetises the iron cap; the cap then produces or changes the magnetic field near the probe. This gives a larger change in the circuit reading than concrete does. [4]
(c) Any two valid changes are acceptable:
- increase the current in the coil;
- use more turns of wire;
- use a soft iron core;
- reduce the resistance of the coil wire.
Each change strengthens the magnetic field, for example more turns or a larger current produces a stronger electromagnet. [4]
(d) Opening the switch breaks the circuit, so no current flows in the coil. The electromagnet's field disappears. Soft iron loses its magnetism quickly when the current stops, so the probe does not strongly attract nearby screws. [4]
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