Multi-Range Meters and Shunt Networks
Each ammeter range obeys equal voltage across the galvanometer and its effective shunt; each voltmeter range obeys V_range = I_g times total series resistance. Ayrton networks must be reduced in the actual switch position.
Why this shows up in the exam
Multi-range ammeter design · Range-switch resistor networks · Instrument calibration across scales
Learn the idea
Range switching changes the external resistance network while protecting the same galvanometer movement. One coil can serve several ranges if switches select different shunts or series multipliers. Every range must still send exactly I_g through the movement at full scale.
🧠 Memory hook: Every switch position must protect the same full-scale coil current.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- I_g G = (I_range - I_g) S_effective — full-scale condition for each ammeter range
- R_total,range = V_range/I_g — required total resistance for each voltmeter range
- R_multiplier = R_total,range - G — series addition for a selected voltage range
How to approach it
- 1Draw the network for one switch position
- 2Apply the full-scale coil condition
- 3Repeat independently for each range and check continuity
Common slip-ups that cost marks
- •Reusing one shunt value for every range
- •Reducing the resistor network in the wrong switch state
- •Momentarily disconnecting the shunt in an unsafe design
🌟 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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