Question

One eV is equal to ______J:
(A) $ 6.5 \times {10^{23}} $
(B) $ 1.9 \times {10^{ - 20}} $
(C) $ 1.6 \times {10^{ - 19}} $
(D) None of the above

Answer 1

Hint :Energy is equal to the product of the charge on a particle and the voltage applied on it. So, we can express it as $ E = qV $ . To find the value of one eV, we will use the definition of one electron volt and put the value of q and V in the above expression. Electron volts or eV is a unit of energy which is equal to the work done by an electron in accelerating it through a potential difference of one volt.

Complete Step By Step Answer:
1 electron volts (eV) is the amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of 1 volt in vacuum.
As we know that 1 electron volt is equal to the work done by an electron in accelerating it through a potential difference of one volt, so $ V = 1\,volt $
We also know that charge on 1 electron is $ 1.6 \times {10^{ - 19}}C $
So, $ 1eV = 1 \times 1.6 \times {10^{ - 19}} \times 1 = 1.6 \times {10^{ - 19}}J $
Thus $ 1eV $ is $ 1.6 \times {10^{ - 19}}J $ .
Hence option (C) is the correct answer.

Note :
Electron volt and Volt are two different kinds of units. Energy is measured in terms of Electron volt whereas electric potential is measured in terms of Volt. Electron volt is very commonly used in physics to express the amount of energy. Various units are used to measure quantities in physics so we must know the basic formula for converting one unit into another. From above, we see that $ neV = n \times 1.6 \times {10^{ - 19}}J $ . Thus, any amount of electron volts can be converted into Joules easily using this formula.