Question

How much power is produced if a voltage of `4 V` is applied to a circuit with a resistance of `64 Omega`?

Answer 1

`P = 0.25 W`
*`W` stands for Watts

Explanation:

You have two given quantities:
-Voltage (`V`) and
-Resistance (`R`).

Then we use the following equations:
(1) `V = I R`
and
(2) `P = I V`

we can do solve the problem in two ways:
(A) solve for `I` and plug it into (2) or (B) we could plug in `I` from (1) and having the expression:

(3) `P= V^2 /R`

Lets first do (A):

(A.1) `I = V/R`
then lets plug in `V` and `R`
(A.2) `I = (4V)/(64Omega)`
(A.2.1)`I = 0.125 Amps`
then plug in (A.2.1) in (2)
(A.3) `P = (0.125 Amp)*(4 V)`
(A.3.1) `P = 0.25W`

then (B):
(B.1) `P = (4V)^2/(64 Omega) = (16V^2)/(64 Omega)`
(B.1.1) `P = 0.25 W`

Hope this helps!