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Energy and Power - Engineering

Q1:

A 15 V source is connected across a 12  resistor. How much energy is used in three minutes?

A 938 Wh

B 0.938 Wh

C 56.25 Wh

D 5.6 Wh

ANS:B - 0.938 Wh

I will assume that this is not in a very hot ambient temperature nor is it sandwiched between other hot components.

In that case, good engineering practice is to use a resistor rated for at least 2x the required power dissipation.

One formula for power is I squared times R.
P = 0.025A^2 x 120 ohms = 0.075W or 75mW.

So, a resistor rated at least double that 150mW.