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Ammeter and voltmeter
Intermediate
Shunts and series resistors extend galvanometer range.
An ammeter is connected in series and should have very low resistance (a galvanometer with a shunt in parallel). A voltmeter is connected in parallel and should have very high resistance (a galvanometer with a series resistor).
Shunt R_s = I_gG/(I − I_g).
Wrong connection can burn an ammeter.
In more detail
An ammeter measures current and is connected in series with a low resistance. A voltmeter measures voltage and is connected in parallel with a very high resistance, so neither disturbs the circuit much.
Real-world uses
- Multimeters switch between ammeter and voltmeter modes.
- Electricians check current and voltage on sites with these meters.
- Electrical meters are built from a sensitive galvanometer, with shunt or series resistors added to change the range.
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Frequently asked questions
Why must an ammeter have low resistance?
So that it does not reduce the current it is measuring.
Why must a voltmeter have high resistance?
So it draws little current and does not change the voltage.
What is a shunt?
A low-resistance path placed in parallel with the galvanometer, so most of the current bypasses the coil for a larger range.
Related topics in Current Electricity & Circuits
Wheatstone bridge · Meter bridge · Potentiometer · Galvanometer · Multimeter · Maximum power transfer