IGCSE Physics (0625) 4.3.1 Circuit diagrams and circuit components Paper 4-2023,2024&2025

Question

(a) The resistance of a circuit component varies with the brightness of the light falling on its surface.
i. State the name of the component.
ii.
Draw the circuit symbol for this component.

(b) Fig. 9.1 shows a 6.0 V battery connected in series with a 1.2 k Ω resistor and a thermistor.

(i) At a certain temperature, the resistance of the thermistor is 2.4 kΩ.
Calculate the reading on the voltmeter.
voltmeter reading =
(ii) The battery connected to the circuit in Fig. 9.1 is not changed.
Suggest a change that would cause the reading of the voltmeter to decrease.

Answer/Explanation

Answer:

(a)(i) LDR OR light-dependent resistor 
(a) (ii)

(b)(i) I = V/R
(total resistance =) 1.2 + 2.4 OR 3.6 seen 
I = 6.0 /(1.2 + 2.4) OR 1.67 or 1.7 (mA) 
(V =) 4.0 V 
OR
\((V^1 )\)= \([R_1/(R_1 +R_2)]\) V
(total resistance =) 1.2 + 2.4 OR 3.6 seen 
(\(V_1\) ) = (2.4 /3.6) 6.0 
= 4.0 V
(b) (ii) Replace the 1.2 kΩ resistor with one of higher value
OR Increase the temperature (of the thermistor or the room)

Question

A student connects the circuit shown in Fig. 8.1.

     

When operating normally, the lamp has a resistance of 10 Ω.

(a) (i) State the current in the lamp when both \(S_1\) and \(S_2\) are open.
………………………………………………………………………………………………………………………
(ii)The student closes switch \(S_1\).
Calculate the current in the lamp, stating the unit of your answer.                
current = ………………………………………….
(iii) The student now closes \(S_2\) as well as \(S_1\).
State the current in the lamp with both switches closed.
………………………………………………………………………………………………………………………

(b) The student decides that she would like to be able to vary the brightness of the lamp.
(i) Name an electrical component that she could add to the circuit to do this.
………………………………………………………………………………………………………………………
(ii) In the space below, redraw the circuit of Fig. 8.1, including the component for varying the lamp brightness.

Answer/Explanation

Answer:
(a) (i)
nothing/ zero/0 
(ii)
V = IR or V/R in words, symbols or numbers 
6/10 
0.6
A OR amp(s) OR ampere(s)
(iii) candidate’s (a)(ii) 

(b) (i) variable resistor OR rheostat
OR potential divider 
(ii) neat, correct circuit with one added component in series with lamp
correct symbol for variable resistor 

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