A solar cell generates a potential difference of 0.1308 V when a 500 resistor is

Question

A solar cell generates a potential difference of 0.1308 V when a 500 resistor is connected across it, and a potential difference of 0.1889 V when a 1000 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 cm2, and the rate per unit area at which it receives energy from light is 2.0m W/ cm2. What is the efficiency of the cell for converting the light energy to thermal energy in the 1000 external resistor? (percent = Do not enter a unit)

Explanation / Answer

Given that, E- ir = V

E - Er/(r+R) = V

So we have, E- E*r/(500+r) = 0.1308

E- E*r/(1000+r) = 0.1889

Dividing this equation by first one,

(1-r/(1000+r))/(1-r/(500+r)) =0.1889/0.1308

Solving the equation, r = 799.2 ohm

Emf E = 0.3399 V

Power received = 5*2 mW = 10 mW = 0.01 W

Power delivered = V^2/R =0.1889^2/1000 = 0.00003568 W

Efficiency = 0.00003568*100%/0.01 = 0.357%

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