A solar cell generates a potential difference of 0.0866 V when a 500 ? resistor is connected across it, and a potential difference of 0.1333 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)