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Figure 9 shows a practical circuit in which a variable resistor is used to control the brightness of a lamp - AQA - A-Level Physics - Question 7 - 2019 - Paper 1
Question 7
Figure 9 shows a practical circuit in which a variable resistor is used to control the brightness of a lamp. The voltmeter reading is monitored as the variable resis... show full transcript
Worked Solution & Example Answer:Figure 9 shows a practical circuit in which a variable resistor is used to control the brightness of a lamp - AQA - A-Level Physics - Question 7 - 2019 - Paper 1
Step 1
Explain why the reading on the voltmeter decreases as the brightness of the lamp increases.
Answer
As the brightness of the lamp increases, more current flows through the circuit. This increase in current leads to a higher voltage drop across the internal resistance of the power source, which in turn reduces the voltage across the lamp. The reading on the voltmeter, which measures this voltage drop, decreases as a result.
Step 2
Explain why V2 is greater than V1.
Answer
When the second cell is connected in parallel with the first, the overall effective internal resistance of the circuit decreases. This decrease in resistance allows more voltage to be available across the load (the lamp), resulting in a higher voltmeter reading V2 compared to V1, which was measured with only one cell.