## 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**

**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**

**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

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