JEE Main 2020 · 5 September · evening · Single correct · +4 / −1
A galvanometer is used in laboratory for detecting the null point in electrical experiments. If, on passing a current of 6 mA it produces a deflection of 2ᵒ, its figure of merit is close to :
- (a) 6 × 10 –3 A/div
- (b) 666ᵒ A/div
- (c) 3 × 10 –3 A/div
- (d) 333ᵒ A/div
Answer and solution
Answer (c) 3 × 10 –3 A/div
Solution
Physics sir · 3 steps
Figure of merit is current per division, so just divide 6 mA by the 2 divisions it moved.
- What it means. The figure of merit G of a galvanometer is the current needed to move the pointer by one division. Here each degree of deflection counts as one division.
G = I/θ = (6 × 10⁻³ A)/(2 div)
- Put in numbers. Write 6 mA as 6 × 10⁻³ A. Then G = 3 × 10⁻³ A/div.
- So. The figure of merit is 3 × 10⁻³ A/div, which is option (c).
The idea to keep. Figure of merit is current divided by deflection, not deflection divided by current. That is why its unit is amperes per division, and a smaller value means a more sensitive galvanometer.
Answer from the NTA final answer key. Solution by PrepWiser.