A technician investigates a light-dependent resistor (LDR) connected in series with a 120 Ω resistor and a voltage source - Edexcel - GCSE Physics - Question 6 - 2015 - Paper 1
Question 6
A technician investigates a light-dependent resistor (LDR) connected in series with a 120 Ω resistor and a voltage source.
The technician measures the voltage acros... show full transcript
Worked Solution & Example Answer:A technician investigates a light-dependent resistor (LDR) connected in series with a 120 Ω resistor and a voltage source - Edexcel - GCSE Physics - Question 6 - 2015 - Paper 1
Step 1
Which one of these circuits should the technician use?
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Answer
The technician should use circuit B. This is because circuit B allows for both the voltage across the LDR and the current through the LDR to be measured accurately.
Step 2
When the LDR is in bright sunlight, its resistance is 185 Ω. The voltage across the LDR is then 7.2 V. Show that the current in the LDR is about 0.039 A.
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Answer
To find the current in the LDR, we can use Ohm's law, which states:
I=RV
Where:
I is the current,
V is the voltage (7.2 V), and
R is the resistance (185 Ω).
Substituting the values into the equation,
I=1857.2≈0.0389A
Thus, the current in the LDR is approximately 0.039 A.
Step 3
An explanation to include (the resistance of the LDR) changes.
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Answer
The resistance of the LDR decreases when exposed to light. In contrast, the LDR has a greater resistance when in the dark. Therefore, its resistance is significantly lower in bright sunlight.
