# Electrical Circuit/Electrical Power Problem

1. May 5, 2010

### lucas101

1. The problem statement, all variables and given/known data

Bob, the environmentally friendly farmer, wants to install a solar-powered system to pump water from his dam to the sheep troughs. The pump will run during daylight hours to fill the troughs. Bob has calculated that the right sized pump for the job pumps a maximum of 20 litres per hour. To pump this much water, it must be connected to a power supply that can provide a voltage of 12V and a current of 1A.

Bob wants to use a certain model solar cell - they are going cheap on ebay. This solar cell will produce a maximum of 1W. When producing this much power, the solar cell has a measured voltage of 6V.

Design a simple electrical circuit that Bob can use to connect his solar cells to his pump. Explain your reasoning, include a drawing of this circuit, and show all relevant calculations."

2. Relevant equations

P = I * V where,

P is the power measured in watts, I is the current measured in Amps and V is the voltage difference measured in Volts.

This is the equation we have been told to use.

3. The attempt at a solution

I calculated the power needed for the pump because this wasn't given and

P = I * V
= 1 * 12
= 12 Watts

At this point im thinking that I may need 12 of these solar cells in parallel to make up the similar power. But then to check this I calculated the current for the solar cell.

P = I * V
1 = I * 6
1/6 amps = I

Now this makes me think that no I need 6 of these in parallel to make up the amperes to the correct level. But then were does that take me with the voltage.

So I guess this confusion is where I'm stuck.

I am actually a biomedical science major and haven't done physics in a while and this problem is frustrating me because it seems like i'm missing some blindingly obvious detail that would easily help me solve the problem.

Help is greatly appreciated.

Luke

2. May 5, 2010

### m.medhat

we will connect two cells' groups on series . each group has 6 cells on parallel . each group has 6 volt 1amp . then the two groups connected on series have 12 volt 1 amp .
i hope you will understand .

3. May 6, 2010

### lucas101

Thankyou, you have given me that nudge that has helped me solve the question! You are a L - wait for it - egend. You are a legend!