An LDR is the lower resistor (R2) in a potential divider. R1 = 5 kΩ and the supply is 10 V. Vout is measured across the LDR. The table shows the resistance ...
Question 1 Report
An LDR is the lower resistor (R2) in a potential divider. R1 = 5 kΩ and the supply is 10 V. Vout is measured across the LDR.
The table shows the resistance of the LDR at different light levels.
| Light intensity / lux | LDR resistance / Ω |
|---|---|
| 100 | 10 000 |
| 200 | 5000 |
| 400 | 2500 |
| 800 | 1200 |
What is Vout when the light intensity is 200 lux?
Answer Details
From the table, at 200 lux the LDR has a resistance of 5000 \(\Omega\) = 5 k\(\Omega\). The LDR is the lower resistor (\( R_2 \)) and \( R_1 = 5 \text{ k}\Omega \), with a 10 V supply.
Using the potential divider formula:
\[ V_{\text{out}} = V_{\text{supply}} \times \frac{R_2}{R_1 + R_2} = 10 \times \frac{5}{5 + 5} = 10 \times \frac{5}{10} = 5.0 \text{ V} \]
When the two resistors in a potential divider are equal, the supply voltage is split equally between them. Each resistor receives exactly half the supply voltage, giving 5.0 V across the LDR.
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