# Thread: Internal Resistance and Solar Cells

1. ## Internal Resistance and Solar Cells

A solar cell generates a potential difference of 0.10 V when a 500 $\displaystyle \Omega$ resistor is connected across it, and a potential difference of 0.15 V when a 1000 $\displaystyle \Omega$ is substituted. What are the (a) internal resistance and (b)emf of the solar cell? (c) The area of the cell is 5.0 $\displaystyle cm^2$, and the rate per unit area at which it receives energy from light is 2.0 $\displaystyle \frac{mW}{cm^2}$. What is the efficiency of the cell for converting light energy to thermal energy in the 1000 $\displaystyle \Omega$ external resistor?

2. a) b) $\displaystyle \epsilon - R_{int}I = V$
$\displaystyle \epsilon = (R_{int}+R_{ext})I$
$\displaystyle \epsilon = V+RI = V+R\frac{\epsilon}{R_{int}+R_{ext}}$
$\displaystyle V= R_{ext}\frac{\epsilon}{R_{int}+R_{ext}}$
Solve for R and then for $\displaystyle \epsilon$

3. c) $\displaystyle P_i = 5 \cdot 2 = 10 \frac{mW}{cell}$
$\displaystyle I = \frac{\epsilon-V}{R_{int}}$
$\displaystyle P_f = IR_{ext}^2$
$\displaystyle \% = \frac{P_f}{P_i}$

4. Thanks. I appreciate the help. There are some problems out of my league.