Question

A conductor carries a current of 60μA. If the area of cross-section of the conductor is 30 mm², then the value of current density is:
1. 0.5 A/m²
2. 2 A/m²
3. 1.5 A/m²
4. 1 A/m²

Answer 1

Correct Answer - Option 2 : 2 A/m²

Concept :

Current density:

The amount of charge per unit time that flows through a unit area of a chosen cross-section is known as current density.

\(J =\frac{i}{A}\)

where J is current density, i is current and A is cross-section area.

Calculation:

Given that, i = 60 μA = 60 × 10^-6 A, A = 30 mm²

here, I = 60 μA = 50 × 10^-6 A

and A = 30 mm² = 30 × 10^-6 m²

then, J = I/A = 60 × 10^-6 / 30 × 10^-6 m²

 J = 2 A/m²

Ohm’s law:

At constant temperature, the potential difference across a current-carrying wire is directly proportional to the current flowing through it.

⇒ V = RI

Electromotive force (e) or e.m.f:

• The electromotive force (e) or e.m.f. is the energy provided by a cell or battery per coulomb of charge passing through it, it is measured in volts (V).
• It is equal to the potential difference across the terminals of the cell when no current is flowing i.e., e = IR