# What is the power - the rate at which it supplies electrical energy?

#### phy112

1. The problem statement, all variables and given/known data
A solar cell provides an emf of 0.70 V.
If the cell supplies a constant current of 20.5 mA for 8.0 h, how much electrical energy does it supply? 413.3 J
What is the power - the rate at which it supplies electrical energy?

2. Relevant equations

P=work/time
units J/s
i keep getting .014

3. The attempt at a solution

#### Jnblose

Re: power

Indeed. Is the 413.3 correct? I'll run a calculation n see what I come up with.

#### Delphi51

Homework Helper
Re: power

Use P = IV to find the power (current in Amperes x potential in Volts).
Electric potential is sometimes called "electromotive force" or "voltage".

Energy is Pt (power x time).
These concepts are often confused with each other. Power is the rate at which energy is provided (or work is done). It is measured in units of Joules per second (also called watts).

Don't forget to convert your mA into A, hours into seconds before using them!

#### mplayer

Re: power

That's what I get too, 0.0144 W. The energy (413.3 J) per time (8hrs = 8*60*60 secs).

Re: power

Thanks!

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