An electric circuit is made up of a $700\,\Omega$ resistor together with a light-dependent resistor (LDR). Fig. 6.1 gives the circuit diagram. The battery has an electromotive force (e.m.f.) of $12\,\text{V}$. An oscilloscope is attached across the fixed resistor. Fig. 6.2 displays the oscilloscope, with the timebase and Y-gain control settings shown. Line Q indicates where the trace lies on the oscilloscope when switch S is open.
(a(i))[1]
Once switch S is closed, the oscilloscope trace shifts to the position marked by line P in Fig. 6.2. Determine the potential difference (p.d.) across the $700\,\Omega$ resistor.
(a(ii))[3]
Determine the resistance of the LDR.
(b)[3]
The intensity of the light falling on the LDR increases gradually. State and explain how the trace on the oscilloscope screen moves.
Worked solution & mark scheme
This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: “The answer is $4.0\text{ V a.c.}$.” …