The diagram shows an electric circuit with two resistors, R and S - Edexcel - GCSE Physics - Question 5 - 2013 - Paper 1

Using Kirchhoff's current law,

$I_{total} = I_R + I_S$

where:

• $I_{total} = 0.60 A$ (total current entering junction)
• $I_R = 0.40 A$ (current through resistor R)

Thus, we can find current in S:

$I_S = I_{total} - I_R = 0.60 \, A - 0.40 \, A = 0.20 \, A$

Therefore, the current in S is 0.20 A.

The voltmeter should be placed:

B in parallel with the battery. This allows the voltmeter to measure the potential difference across the battery.

When a current passes through a resistor, it encounters resistance. This resistance causes energy to be dissipated in the form of heat due to collisions between charge carriers (like electrons) and the lattice structure of the material. This leads to an increase in the temperature of the resistor.

LDRs (Light Dependent Resistors) change their resistance based on light intensity. In bright light, the resistance is low, allowing more current to flow, whereas in darkness, the resistance is high, reducing the current. This property can be used in circuits to adjust the current based on surroundings.

Thermistors also change resistance with temperature. An NTC (Negative Temperature Coefficient) thermistor decreases its resistance as temperature increases, allowing more current to flow when it gets hot. Conversely, a PTC (Positive Temperature Coefficient) thermistor increases resistance with temperature, decreasing current flow when heated. Both components are widely used in temperature sensing and automatic control systems.