Fig. 6.1 presents a circuit diagram that includes a battery, a light-dependent resistor (LDR) and a fixed resistor with resistance $240\,\Omega$ joined in series. A lamp is positioned close to the circuit. When the lamp is turned on, light from it falls on the LDR.
Fig. 6.2 gives the current-voltage graph for the LDR with the lamp turned on and with the lamp turned off. The vertical axis shows current/A and the horizontal axis shows voltage/V.
(a)[2]
State the law of Ohm.
(b)[1]
Explain how the graph lines in Fig. 6.2 show that the LDR obeys Ohm’s law.
(c)[2]
Use values from Fig. 6.2 to explain how light changes the resistance of the LDR.
(d(i))[1]
When the lamp is switched on, the current in the LDR is $0.050\,\text{A}$. Determine the current in the fixed resistor.
(d(ii))[3]
Calculate the cell electromotive force (e.m.f.).
Worked solution & mark scheme
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