# In an element, let w be the energy, and q be the charge, what is the voltage across the element?

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In an element, let w be the energy, and q be the charge, what is the voltage across the element?
1. w + q
2. w - q
3. w × q
4. $\frac{{dw}}{{dq}}$

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Correct Answer - Option 4 : $\frac{{dw}}{{dq}}$

One Volt is equivalent to one Joule per Coulomb.

If the electrical potential difference between two points is 1 volt, then one Coulomb of charge will gain 1 joule of potential energy when moved between those two points, i.e.

$1Volt = \frac{{1Joule}}{{1Coulomb}}$

∴ The voltage across the element is defined as the rate of change of energy per unit charge, i.e.

$V=\frac{{dw}}{{dQ}}$