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Practice MCAT Question - Q42 - Answer!

A 12 Ohm load is connected across a 6.0 V dc source. How much energy does the load use in half an hour?

A.  1.5 x 10-3 kWh
B.  2.0 x 10-3 kWh
C.  3.0 x 10-3 kWh
D.  12 x 10-3 kWh

The correct answer is (A). The energy used by a load is the product of the power it uses per unit time and the length of time it is operated:

E = W = Pt = V2t/R
    = (6.0 V)2 (0.50 h)  / 12 Ohm
    =  1.5 x 10-3 kWh

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