13A

YOUR ANSWER: 250 watts.

Not quite.

Again, the values given here, current flow at .5 ampere through a resistance of 500

ohms.

Let's see how we solve this problem.

a. Use the correct formula: P - I2R.

b. P =.5 X.5 X 500

c. P=.25x500

d. P=?

We arrive at the formula P - I2R by using a variation of Ohm's law. P = E x I in our basic

power formula. E = IR in the variation of Ohm's law. Substituting IR for E in our power

formula, we get P = IR x I or P = I2R.

Return to frame 8B and solve for the correct answer.

13B

YOUR ANSWER: Ohms.

True. But you seem to be forgetting that heat is generated when current flows through

a resistance. Heat being energy, it must have been created in this case by the conversion of

electrical energy to heat energy. How much heat the resistor can consume before it will char

or crack depends a lot on its physical size, especially with the carbon resistor; the larger it is,

the more heat it can absorb and give up. So not only do we have to know the ohmic value, but

we much also know how much current and voltage it will handle, since P = E x I.

With this in mind, return to frame 18A.

IT0348

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