9A

YOUR ANSWER: 10 watts.

Good. You are remembering that P = E x I in our basic power formula. When current flows in a

resistance, heat is produced. The heat energy is evidence that power is used in producing current in a

resistance. The power is generated by the source of applied voltage and consumed in the resistance in

the form of heat.

It is convenient, then, to have a power formula to express power in watts in terms of resistance.

For current:

P = I2R.

For voltage:

P = E2.

R

P = E x I = 6 x 2 = 12 watts.

P = I2R = 4 x 3 = 12 watts.

P = E2 = 36 = 12 watts.

R

3

If you knew the voltage and resistance in a circuit, which formula would you use to solve for

power?

P = E2.

frame 4B

R

P = E x I.

frame 7B

9B

YOUR ANSWER: 750 watts.

Again, we answer your answer with, not quite.

The formula again is P I2R, not P = IR; you forgot to square I in your solution.

Go back to frame 11A and try again.

IT0348

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