Question

A certain flux meter has the following specifications:

Air gap flux density = 0.05 Wb/m²

Number of turns on moving coil = 40

Area of moving coil = 750 mm²

If the flux linking 10 turns of a search coil of 200 mm² area connected to the flux meter is reversed in a uniform field of 0.5 Wb/m², then the deflection of the flux meter will be
1. 87.4°
2. 76.5°
3. 65.6°
4. 54.7°

Answer 1

Correct Answer - Option 2 : 76.5°

Air gap flux density = 0.05 Wb/m²

No. of turns on moving coil = 40

Area of moving coil = 750 mm²

N = 10, B = 0.5 Wb/m²

A = 200 mm²

Constant of flux meter, G = NBA

G = 40 × 0.05 × 750 × 10^-6 = 1500 × 10^-6

Flux linking with the coil

= 0.5 × 200 × 10^-6

= 100 × 10^-6 Wb

Change in flux linking the coil

= 2 × 100 × 10^-6 (Since flux meter is reverse)

= 200 × 10^-6

∴ Change in flux, \(\phi = \frac{G}{N} \times \theta\)

\(\therefore \theta = \frac{N}{G}\phi = \frac{{10}}{{1500\; \times \;{{10}^{ - 6}}}} \times 200 \times {10^{ - 6}}\;rad\) 

\(= \frac{4}{3}\;rad\) 

⇒ θ = 76.5°