A solar cell generates a potential difference of 0.0966 V when a 500 Ohm resisto

Question

A solar cell generates a potential difference of 0.0966 V when a 500 Ohm resistor is connected across it, and a potential difference of 0.1436 V when a 1000 Ohm resistor is substituted. What is the internal resistance of the solar cell? What is the emf of the solar cell? The area of the cell is 5.0 cm^2, and the rate per unit area at which it receives energy from light is 2.0m W/cm^2. What is the efficiency of the cell for converting the light energy to thermal energy in the 1000 ohm external resistor? (percent = Do not enter a unit)

Explanation / Answer

current I1 = V1/R1 = 0.0966/500 = 0.0001932 A

current I2 = V2/R2 = 0.1436/1000 = 0.0001436 A

V1 = E - I1*r

V1 = E - V1*r/R1 .......(1)

V2 = E - I2*r

V2 = E - V2*r/R2 .......(2)

(2) - (1)

V2 - V1 = r*(V1/R1 - V2/R2)

0.1436 - 0.0966 = r*(0.0966/500 - 0.1436/1000)

internal resistance r = 947.6 ohms

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Emf E = V1 + V1*r/R1

E = 0.0966 + (0.0966*947.6/500)

E = 0.279 v

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total power of the cell P1 = 2*5 = 10 mW

toal energy in 1000 ohm resistor P2 = v2^2/R2 = 0.1436^2/1000 = 0.0206 mW

efficiency = P2/P1*100 = 0.2 %

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