01. What is an electric current?
Ans: Electric current is the amount of charge flowing through a particular area in unit time. Or the rate of flow of electric charges [electrons] is called electric current. The force that move the electrons comes from cell. If a net charge Q, flows across any cross-section of a conductor in time t, Therefore, The current I = Q/t.
The SI unit of electric charge is coulomb (C), which is equivalent to the charge contained in nearly 6 × 10 18 electrons- 19
1 coulomb = n x (1.66 x 10-19)
n = 1/1.66 x 10 -19 = 6.25x1018 =6 x10 18
2. A current of 0.5 A is drawn by a filament of an electric bulb for 10 minutes. Find the amount of electric charge that
flows through the circuit.
Ans. Charge on 1 electron = - 1.6 × 10 C.
The electric current is expressed by a SI unit [ampere] = A
⇒ 1A = 1C/1sec
Hence, When one coulomb of charge flows through a conductor for 1 second then current flowing through it is called
One ampere.
⇒ An instrument called ammeter is used to measures electric current in a circuit.
⇒ The electric current flows in the circuit from the positive terminal of the cell to the negative.
3. Why is an ammeter always connected in series in a circuit?
Ans: Ammeter is always connected in series in a circuit so that the value of the current in the ammeter remains same independent of its position in the electric circuit.
4. Calculate the number of electrons constituting one coulomb of charge.
Ans: Charge (Q) = no. of electrons (n) x charge on one electron (e)
I = 0.5 A;
t = 10 min = 600 s.
We have I = Q/t ⇒ Q = It = 0.5 A × 600 s = 300 C
5. Electric current was considered to be the flow of positive charges and the direction of flow of positive charges was
taken to be the direction of electric current. Why?
Ans: This is because electrons were not known at the time when the phenomenon of electricity was first observed. Conventionally, in an electric circuit the direction of electric current is taken as opposite to the direction of
the flow of electrons, which are negative charges.
