Question

A Wheatstone bridge requires a change of 7 Ω in the unknown resistance arm of the bridge to produce a change in deflection of 3 mm of the galvanometer. The sensitivity and the deflection factor will be nearly
1. 0.23 mm/Ω and 2.3 Ω/mm
2. 0.43 mm/Ω and 2.3 Ω/mm
3. 0.23 mm/Ω and 1.3 Ω/mm
4. 0.43 mm/Ω and 1.3 Ω/mm

Answer 1

Correct Answer - Option 2 : 0.43 mm/Ω and 2.3 Ω/mm

Concept:

Deflection sensitivity of a Wheatstone bridge:

• It is defined as the deflection in the galvanometer per unit current.
• In the unbalanced condition of the bridge, when current flows, it causes the pointer of galvanometer to get deflected. Thus, the deflection rate is the function of sensitivity.
• As the change in current is dependent on the change in resistance, it is also defined as the change in deflection to the change in resistance.
• It is expressed in mm/Ω

 

Deflection sensitivity = change in deflection/change in resistance

Deflection factor:

It is reciprocal of deflection sensitivity. It is expressed in Ω/mm.

Calculation:

Given that, change in deflection = 3 mm

Change in resistance = 7 Ω

Deflection sensitivity = 3/7 = 0.43 mm/Ω

Deflection factor = 7/3 = 2.3 Ω/mm