The SI unit for Luminous intensity is candela. Its symbol is cd.
Definition:
One candela is the luminous intensity in a given direction, of a source that emits monochromatic radiation of frequency 5.4\(\times\) 10⁴ Hz and that has a radiant intensity of \({{1}\over{638}}\) watt/steradian in that direction.

The SI unit for electric current is ampere (A)
Definition:
One ampere is the constant current, which when maintained in each of the two straight parallel conductors of infinite length and negligible cross section, held one metre apart in vacuum shall produce a force per unit length of 2\(\times\)10^-7N/m between them.

Fundamental units:
The units in which the fundamental quantities are measured are called fundamental units. It is also known as base units.
Derived units:
The units of measurements of all other physical quantities, which can be obtained by a suitable multiplication or division of powers of fundamental units are called derived units.
Example:
Unit of speed = \({{Unit\ of\ distance}\over{Unit\ of\ \ time}}\)
\(={{m}\over{s}}={ms}^{-1}\)
ms^-1 is a derived unit.

Fundamental quantities:
Fundamental quantities are quantities which cannot be expressed in terms of any other physical quantity. 
Example: Quantities like length, mass, time, temperature are fundamental quantities.
Derived quantities:
Quantities that can be expressed in terms of fundamental quantity are called derived quantities.
Example: Quantities like area, volume, velocity are derived quantities.

(i) Basic laws of electricity and magnetism led to the discovery of wireless communication technology which has shrunk the world with effective communication over large distances.
(ii) The launching of satellite into space has revolutionized the concept of communication.
(iii) Microelectronics, lasers, computers, superconductivity and nuclear energy have comprehensively changed the thinking and living style of human beings.