Galvanometer Figure of Merit and Calibration
If a current I produces n scale divisions, the galvanometer figure of merit is K = I/n in ampere per division. For a reading n, I = Kn; angular calibration similarly uses I/theta.
Why this shows up in the exam
Calibrating a galvanometer scale · Converting deflection to current · Comparing instrument response constants
Learn the idea
The figure of merit is the current needed per scale division, so it links measured current to observed deflection. Calibration tells how much current corresponds to one division. Once that constant is known, any scale reading can be converted directly to current, subject to zero and linearity checks.
🧠 Memory hook: Figure of merit is current per division, not divisions per current.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- K = I/n — figure of merit in ampere per scale division
- I = K n — current corresponding to n divisions
- K_theta = I/theta = k/(NAB) — angular figure of merit from torque balance
How to approach it
- 1Identify whether deflection is divisions or angle
- 2Use the matching calibration constant
- 3Check units before converting the reading
Common slip-ups that cost marks
- •Taking the reciprocal definition
- •Mixing divisions with radians
- •Ignoring zero offset or nonlinear scale behavior
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
A charge of 2 microC moves perpendicular to a 3 T magnetic field at 4 x 10^5 m/s. Find the magnetic force.
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