Electric Current

Class XII :  NCERT Chapter 3  :  Current Electricity

Q: What is electric current?

Ans: The rate of flow of charge in a definite direction is called electric current.

Mathematically, current (I) =   (charge flown, q) / (time taken, t)

Q: What are the charge carriers in (a) solid conductors (b) electrolytes (c) gases?

Ans: The charge carriers

(a) in solids are the free valence electrons.

(b) in electrolytes are the ions, both cations and anions.

(c ) in gases are both positive ions and electrons. Gases are normally insulators, but ionized gases at high potential difference and low pressure can conduct electricity.

Q: What is an electric cell?

Ans: An electric cell is a source of electrical energy. This electrical energy may be obtained by converting chemical energy into electrical energy (chemical cells), or, by converting solar energy into electrical energy (solar cell) etc.

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Q: What is E.M.F. of a cell? What is its unit?

Ans: E.M.F. stands for Electromotive force. It is defined as the maximum potential difference between the two electrodes of a cell when no current is drawn from the cell (i.e. when the cell is in open circuit).

Its SI unit is volt (V).

Q: Electric current is scalar or vector quantity?

Ans: Electric current is a scalar quantity. The reason is that though current has direction, it does not obey the law vector addition; it adds up algebraically.

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