During a night survey, ecologists place an electronic bird-call recorder beside a wetland. Fig. 1 shows the 6.0 V battery circuit that powers a small sounde...
Question 1 Report
During a night survey, ecologists place an electronic bird-call recorder beside a wetland. Fig. 1 shows the 6.0 V battery circuit that powers a small sounder used to check that the recorder has started. The sounder takes a current of 0.30 A when the switch is closed. It operates for 120 s at the beginning of each survey. The sounder is designed to transfer some electrical energy into sound waves, but its casing also becomes slightly warm. A resistor limits the current so that the battery cells and connecting wires do not overheat.
(a) What is meant by electric current? [1]
(b) Calculate the charge passing through the sounder in 120 s. Use charge = current x time. [2]
(c) Calculate the electrical energy supplied by the battery in this time. Use energy = voltage x charge. [2]
(d) Describe the useful and wasted energy transfers in the sounder. [2]
(e) Give the resistance of the sounder and resistor together. Use resistance = voltage / current. [2]
(f) Which component could be added in series to protect the circuit if a fault causes a very large current? [1]
Answer Details
(a) Electric current is the rate of flow of electric charge. [1]
(b) Use \(Q=It\):
\[Q=0.30\ \mathrm{A}\times120\ \mathrm{s}=36\ \mathrm{C}\]
The charge is 36 C. [2]
(c) Use \(E=VQ\):
\[E=6.0\ \mathrm{V}\times36\ \mathrm{C}=216\ \mathrm{J}\]
The battery supplies 216 J. [2]
(d) Electrical energy is transferred to sound energy, which is useful for the sounder. Some is transferred to thermal energy in the sounder and casing, which is wasted. [2]
(e) Use \(R=V/I\):
\[R=\frac{6.0\ \mathrm{V}}{0.30\ \mathrm{A}}=20\ \Omega\]
The combined resistance is 20 \(\Omega\). [2]
(f) Add a fuse in series. It melts and breaks the circuit if a fault produces an excessive current. [1]
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