In SI system, the unit of P.E is
A) erg
B) dyne-cm
C) Joule
D) None of these

Hint- P.E is a short form of potential energy. The object can store energy according to the position of the object. The energy is stored in the form of potential energy when the object is at rest. The value of potential energy varies according to the object’s distance from the unit positive charge. The total energy of the object is the sum of potential energy and kinetic energy.

Complete step by step answer:

In earlier days, every quantity was measured in CGS form of units. Later it was transformed into the MKS system. This MKS system is now called SI units.

The amount of energy required in moving unit positive charge from one point to another is called potential energy. It is measured in many units. They are erg, electron volt, joule, etc.

Among these units, the erg is the unit used in the CGS system. And the Joule is used in the SI system.

(iv) Hence the correct option is C.

Additional information:

In 1832, the CGS system was proposed by the German mathematician Gauss. Later in 1873, this system was adopted by the British association. But in the 20th-century scientists felt that this system is inconvenient for many practical purposes.

Hence many of the CGS system units were replaced by the MKS units. This replaced the two fundamental units of CGS, centimetre, and gram with the meter and gram for length and the mass respectively. This MKS system was later accepted as the International units to measure and this is now called SI units.

Note: SI units have many advantages over the CGS units. The SI system has seven basic units. It is more rational than it gives one unit to one quantity. For example, energy is denoted only in the unit called ‘Joule’. In any language, the SI units are the same and it is not subject to change. It is more coherent and modernized.