# Physics Questions and Answers – Electric Current

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This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Electric Current”.

1. What is the SI unit of current?
a) Coulomb (C)
b) Ampere (A)
d) Newton (N)

Explanation: The SI unit of current is Ampere (A). The current through a wire is called one ampere if one coulomb of charge flows through the wire per second.
1 Ampere = $$\frac {1 \, Coulomb}{1 \, Second}$$ or 1A = 1Cs-1.

2. What is the number of electrons that constitutes a current of one Ampere?
a) 2.25 × 1018
b) 2.25 × 10-18
c) 6.25 × 1018
d) 6.25 × 10-18

Explanation: Number of electrons, n = $$\frac {Current (I) \times time (t)}{Charge \, of \, 1 \, electron (e)}$$
= $$\frac {(1 \times 1)}{1.6 \times 10^{-19}}$$
= 6.25 × 1018.

3. Give the number of electrons passing through a wire per minute. The current flowing through it is 500mA.
a) 1.875 × 1020
b) 6.875 × 1020
c) 1.875 × 10-20
d) 6.875 × 10-20

Explanation: Number of electrons, n = $$\frac {It}{e}$$.
= $$\frac {(500 \times 10^{-3} \times 60)}{(1.6 \times 10^{-19})}$$
= 1.875 × 1020.

4. Which of these is a correct definition of conventional current?
a) Current that flows from lower potential to higher potential
b) The current which remains static
c) Current constituted by the flow of ions
d) Current that flows from higher potential to lower potential

Explanation: The current that flows from a point at the higher (positive) potential to a point at lower (negative) potential is called conventional current. The direction of motion of positive charges is taken as the direction of electric current.

5. Which type of current is flowing through a circuit?
a) Static current
b) Conventional current
c) Electronic current
d) Potential current

Explanation: The carriers of electric current are electrons. The current in a circuit is due to the flow of electrons. Therefore, the direction of the conventional current is opposite to the direction of flow of electrons.

6. In electrolytes and ionic crystals, the current carriers are free electrons.
a) True
b) False

Explanation: In electrolytes and ionic crystals, the current carriers are positive and negative ions. Whereas in most of the substances like metals, the carriers of electric current are electrons.

7. Identify the dimensional formula of electric current.
a) [M L T-2]
b) [M0 L0 T0 A1]
c) [M L3 T0]
d) [M L2 T-3]

Explanation: The flow of charge per unit time is defined as current. The fundamental unit of current is Ampere (named after Andre Marie Ampere).
Hence the dimensional formula of electric current is [M0 L0 T0 A1].

8. Which type of a physical quantity is electric current?
a) Scalar quantity
b) Vector quantity
c) Bipolar quantity
d) Thermodynamic quantity

Explanation: The electric current is a scalar quantity. Laws of ordinary algebra are used to add electric currents and the law of vector algebra are not applicable.

9. Which of these is a correct definition of electronic current?
a) Current that flows from lower potential to higher potential
b) The current which remains static
c) Current constituted by the flow of ions
d) Current that flows from higher potential to lower potential

Explanation: The current that flows from a point at the lower (negative) potential to a point at higher (positive) potential is called electronic current. Electronic current is produced by the movement of negatively charged electrons.

10. What is the study of electric charges in motion called?
a) Charge mobility
b) Electronic mobility
c) Static electricity
d) Current electricity