Question

Which of the following is not used as the unit of work?
A. Erg
B. Joule
C. Electron volt
D. Volt

Answer 1

Work is measured as the component of force along the direction of motion times the displacement of the object acting under the certain motion. Since, forces are measured in Newton, and we multiply by a distance in order to obtain work, work is measured in Newton-meters or Joules.

Formula Used: The work done is given by: $W = \vec F.\vec S = FS\cos \theta = (F\cos \theta )S$

where, $F$is the component of force along the direction of motion and $S$ is the displacement.

Complete step by step solution: The work is said to be done by a force, when point of application undergoes a displacement. This work done is given by the scalar product of force and the displacement.

$W = \vec F.\vec S = FS\cos \theta = (F\cos \theta )S$

where, $F$is the component of force along the direction of motion and $S$ is the displacement.

So, the units of Work are Newton-meter. (Since Newton is the unit of Force and meter is the unit of displacement). The unit Newton-meter can also be written as Joules. Thus, Joule is also used as the unit of work.

1-Joule can be written as: $1Joule = {10^7}erg$. Thus, erg can also be used as a unit of work.

The unit Electron volt is mostly used in atomic and nuclear physics. It is used to represent the energy of an electron. For example, whenever an electron makes a transition between valence band and conduction band, it emits or absorbs energy that is measured in Electron volt. The energy band gap can also be measured in Electron volt. Thus, Electron volt can also be used as the unit of work.

Volt is the electrical unit of voltage or potential difference. The unit of Volt is Joule/Coulomb. Thus, Volt cannot be used to measure Work.
Hence, option (D) is the correct answer.

Note: The Electron-Volt is the energy defined by an electron. It can also be defined as the energy gained by an electron when the electrical potential at the electron increases by one Volt. 1 Electron- Volt can be measured in terms of Joule such as:

$1eV = 1.602 \times {10^{ - 19}}Joule.$

Joule is a derived unit of energy in the International System of units or SI units. Relation
between Electron-Volt and Joule is proportionate. Change in the value of Electron-Volt will change the Joule equivalent value in the same proportion.