Voltage

Consider a portable battery charger for a phone needs to deliver 20 W of power for fast charging. If the current passing through is 4 amps, what is the battery’s output voltage (V)?

Expand Hint
Power absorbed by a resistive element:
$$$P=VI=\frac{V^{2}}{R}=I^2R$$$
where $$V$$ is voltage, $$I$$ is current, and $$R$$ is resistance.
Hint 2
Based on the problem statement’s givens, solve for voltage using the equation:
$$$P=VI$$$
Power absorbed by a resistive element:
$$$P=VI=\frac{V^{2}}{R}=I^2R$$$
where $$V$$ is voltage, $$I$$ is current, and $$R$$ is resistance.

Solving for Voltage using the problem statement’s knowns:
$$$P=VI\rightarrow 20W=V(4A)$$$
$$$V=\frac{20W}{4A}=5\:V$$$
5 V