12 V power supply A heating coil A technician tests a heating coil used to keep a reptile enclosure warm. Fig. 1 shows the circuit before the enclosure is c...
Question 1 Report
A technician tests a heating coil used to keep a reptile enclosure warm. Fig. 1 shows the circuit before the enclosure is connected to the mains supply. The power supply is set to 12 V and the ammeter reads 2.0 A. The coil becomes hot because electrical energy is transferred to thermal energy. The technician checks the current first, since a current that is too large could damage the cable insulation and create a safety risk.
(a) Give the equation linking potential difference, current and resistance. [1]
(b) Calculate the resistance of the coil. [2]
(c) Describe the energy transfer in the coil. [1]
(d) Explain why the coil has a greater resistance than a short thick copper cable. [1]
Answer Details
(a) The relationship is \(V=IR\). [1]
(b) Rearranging gives \(R=V/I\):
\[R=\frac{12\text{ V}}{2.0\text{ A}}=6.0\ \Omega\]
[2]
(c) In the heating coil, electrical energy is transferred to thermal energy. [1]
(d) The coil has greater resistance because it is made of a higher-resistivity material and is much longer and thinner than a short thick copper cable. [1]
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