A recycling crane uses an electromagnet to lift iron lids from a box of mixed waste. Fig. 1 shows the coil wound around an iron core. The power supply provi...
Question 1 Report
A recycling crane uses an electromagnet to lift iron lids from a box of mixed waste. Fig. 1 shows the coil wound around an iron core. The power supply provides 12 V and the resistance of the coil is 4.0 ohms when it is operating. A switch allows the crane driver to release the lids quickly.
(a) State why iron, rather than aluminium, is used for the core. [2]
(b) Calculate the current in the coil. [3]
(c) Explain what happens to the magnetic field when the driver opens the switch. [4]
Answer Details
(a) Iron is magnetic and can be magnetised. [1] Aluminium is not magnetic and does not become strongly magnetised. [1]
(b) \[I=\frac{V}{R}\] [1]
\[I=\frac{12\text{ V}}{4.0\text{ Ω}}\] [1]
\[I=3.0\text{ A}\]
The current is 3.0 A. [1]
(c) Opening the switch breaks the circuit. [1] The current in the coil stops. [1] Without current, the coil no longer produces an electromagnet field. [1] The iron core loses most of its magnetism, so the lids fall. [1]
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