Fig. 1 shows the current-voltage graph for a filament lamp used in a theatre prop. The student obtained each point by changing the supply voltage and waitin...
Question 1 Report
Fig. 1 shows the current-voltage graph for a filament lamp used in a theatre prop. The student obtained each point by changing the supply voltage and waiting briefly before reading the current. Unlike a fixed resistor at constant temperature, the graph becomes less steep as the voltage rises because the filament becomes very hot. At 6.0 V, the current is 0.50 A.
(a) State how the current changes as the voltage increases from 0 V to 8 V. [1]
(b) Explain why the graph becomes less steep at higher voltages. [3]
(c) Calculate the power of the lamp at 6.0 V. [2]
(d) Calculate the energy transferred by the lamp operating at 6.0 V for 4.0 minutes. [3]
(e) Describe how an ammeter and a voltmeter are connected when obtaining this graph. [2]
Answer Details
(a) As voltage increases from \(0\ \mathrm{V}\) to \(8\ \mathrm{V}\), the current increases [1].
(b) At a higher voltage there is a larger current and more heating of the filament [1]. The filament temperature rises [1], increasing its resistance. Therefore each further increase in voltage produces a smaller increase in current, so the graph becomes less steep [1].
(c) At \(6.0\ \mathrm{V}\), the current is \(0.50\ \mathrm{A}\):
\[P=VI=6.0\ \mathrm{V}\times0.50\ \mathrm{A}=3.0\ \mathrm{W}\]
Power = \(3.0\ \mathrm{W}\) [2].
(d) Convert minutes to seconds:
\[t=4.0\times60=240\ \mathrm{s}\]
\[E=Pt=3.0\ \mathrm{W}\times240\ \mathrm{s}=720\ \mathrm{J}\]
Energy transferred = \(720\ \mathrm{J}\) [3].
(e) The ammeter is connected in series with the lamp [1]. The voltmeter is connected in parallel across the lamp [1].
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