Question

An iron-cored coil has an inductance of 4 H. If the reluctance of the flux path is 100 AT/Wb, then the number of turns in the coil is:
1. 400
2. 200
3. 20
4. 40

Answer 1

Correct Answer - Option 3 : 20

Concept:

Self-inductance \(L = \frac{{{{\rm{μ }}_0}{{\rm{μ }}_{\rm{r}}}{\rm{A}}{{\rm{N}}^2}}}{l}\)

Here, A = Area

N = Number of turns

l = Length of coil

magnetic flux \(ϕ = \frac{{{{\rm{μ }}_0}{{\rm{μ }}_{\rm{r}}}{\rm{A}}{{\rm{N}}{I}}}}{l}\)

Reluctance \(s = \frac{{{N^2}}}{L}\).......(i)

Calculation:

L = 4 H, s = 100 AT / Wb

From equation (i)

\(N = \sqrt {4 \times 100} \)

= 20