Converting a Galvanometer into a Voltmeter
For galvanometer resistance G and full-scale current I_g converted to voltmeter range V, series resistance R satisfies V = I_g(G + R), so R = V/I_g - G.
Why this shows up in the exam
Designing voltmeter ranges · Finding multiplier resistance · Comparing loading effects
Learn the idea
A large series resistance limits current so a galvanometer can measure a larger voltage. The added resistor drops most of the applied voltage while keeping coil current at or below its safe full-scale value.
🧠 Memory hook: Voltmeter means a large resistor in series.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- R = V/I_g - G — series resistance required for voltmeter range V
- R_V = G + R = V/I_g — total voltmeter resistance
- V_g = I_g G — bare galvanometer full-scale voltage
How to approach it
- 1Set the safe coil current to I_g
- 2Write total series resistance V/I_g
- 3Subtract the coil resistance
Common slip-ups that cost marks
- •Putting the multiplier in parallel
- •Forgetting to subtract G
- •Using the desired voltage as the drop only across the added resistor
🌟 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.
More from Magnetic Effects of Current and Magnetism
Magnetic field due to currents
Learn how electric currents produce magnetic fields, including the use of Biot-Savart law, Ampere's law, and the calculation of fields for various conductor shapes such as straight wires, circular loops, and solenoids.
Magnetic moment and properties of magnets
Explore the concept of magnetic moment for current loops and bar magnets, properties of divided magnets, and effective length of magnets.
Magnetic properties of materials
Learn about diamagnetic, paramagnetic, and ferromagnetic materials, their magnetic susceptibility, temperature dependence, Curie temperature, and the role of domains.
Force and motion in magnetic fields
Understand the forces experienced by current-carrying conductors and moving charges in magnetic fields, including the Lorentz force, force between parallel conductors, and the motion of charged particles.
Magnetic dipoles and torque
Study the behavior of magnetic dipoles in magnetic fields, including torque, potential energy, and the vector addition of dipole moments.
Galvanometer conversion and measurement devices
Understand how to convert a galvanometer into an ammeter or voltmeter using shunt and series resistances, and the principles behind these measuring instruments.