A photoresistor, whose resistance decreases with light intensity, is connected i

Question

A photoresistor, whose resistance decreases with light intensity, is connected in the circuit of the figure. On a sunny day, the photoresistor has a resistance of 0.62 k? . On a cloudy day, the resistance rises to 4.0 k? . At night, the resistance is 24 k?.

A. What does the voltmeter read on a sunny day?

V= _________

B. What does the voltmeter read on a cloudy day?

V=__________

C. What does the voltmeter read at night?

V=__________

D. Does the voltmeter reading increase or decrease as the light intensity increases? (multiple choice)

1. The voltmeter reading increases because the current through the resistor decreases. 2. The voltmeter reading decreases because the current through the resistor decreases. 3. The voltmeter reading increases because the current through the resistor increases. 4. The voltmeter reading decreases because the current through the resistor increases.

Explanation / Answer

The photoresistor has resistance sunnay day R1 = 0.62

The photoresistor has resistance cloudy day R1 = 4.0k

The photoresistor has resistance at night       R1 = 24k

Part A -What does the voltmeter read on a sunny day

From the figure the equivalent resistance

       Req = (0.62) + 1.0*10^3

              = 1000.62

then the current in the circuit I = 9V/1000.62 = 0.00899A

therefore the voltmeter reading VR1 = (1000)(0.00899) = 8.99V

Part B- What does the voltmeter read on a cloudy day

From the figure the equivalent resistance

       Req = 4.0 k + 1.0*10^3

              =5.0*10^3

then the current in the circuit I = 9V/5000 = 0.0018

therefore the voltmeter reading VR2 = (1000)(0.002045) = 1.8 V

Part C- What does the voltmeter read at night

From the figure the equivalent resistance

       Req = 24k + 1.0*10^3

              =25*10^3

then the current in the circuit I = 9V/25000 = 0.00036 A

therefore the voltmeter reading VR2 = (1000)( 0.00036A) = 0.36V

Part D- As the light intensity increases the voltmeter reading increases

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