Galvanometer Symbol
Definition: The Galvanometer symbol represents a sensitive moving-coil instrument for detecting and measuring small electric currents, drawn per IEC 60617 indicating-instrument convention as a circle containing the letter G (often with a needle line), with polarised + and − terminals because the needle's deflection direction depends on current direction.
Also known as: galvanometer, moving-coil galvanometer, D'Arsonval meter, current detector, null detector, centre-zero meter, deflection meter.
What the Galvanometer symbol means
The galvanometer symbol denotes the most sensitive of the classic analogue indicating instruments: a moving coil suspended in a permanent-magnet field that rotates in proportion to the current through it (the D'Arsonval movement). Where an ammeter measures amps and a voltmeter volts, the galvanometer detects microamps — its historical role is not so much measuring current as detecting whether any current flows at all, and in which direction. Many galvanometers are centre-zero, deflecting left or right depending on current polarity, which is why the symbol's + and − pins matter.
In modern practice the galvanometer survives mainly in education and in null-detection: it is the detector in the Wheatstone bridge and potentiometer experiments, where the goal is to adjust the circuit until the galvanometer reads exactly zero (the 'null'), indicating perfect balance. Physics curricula (GCSE through university, and class 10–12 syllabi in India) also use it to teach how one basic movement becomes an ammeter or a voltmeter by adding external resistors.
How to identify the Galvanometer symbol
Draw a circle with a capital G inside — that is the whole symbol in both IEC and ANSI conventions, following the general rule that indicating instruments are circles containing their quantity letter (A for ammeter, V for voltmeter, W for wattmeter, G for galvanometer). Some renderings add a short needle line pivoting from the bottom of the circle to suggest the pointer, and centre-zero types may show a small scale arc.
The only real identification hazard is confusing the G-in-circle galvanometer with a generator, which some standards also mark 'G' in a circle. Context resolves it: a generator is a source feeding power into the circuit (usually with a shaft or drive notation), while a galvanometer sits in a measuring branch, typically in series with a bridge detector arm, and carries + / − terminal marks.
Function in a circuit
A galvanometer's coil sits in the field of a permanent magnet; current through the coil produces a torque proportional to current (F = BIL physics), opposed by a hairspring, so the needle's steady deflection is linearly proportional to current. Full-scale deflection typically requires only tens of microamps to a few milliamps, and the coil resistance is tens to hundreds of ohms — connecting a galvanometer directly across a battery will destroy it.
Its two derived roles define classic instrument design: adding a low-resistance shunt in parallel diverts most of the current and turns it into an ammeter of any desired range; adding a high-resistance multiplier in series turns it into a voltmeter. As a null detector in a Wheatstone bridge, its job is different — maximum sensitivity around zero so that even a microamp of imbalance produces visible deflection, letting resistance be measured by balance rather than by absolute reading.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617 draws indicating instruments as a circle enclosing the quantity symbol; a galvanometer uses the letter G (IEC 60051 governs the performance and accuracy classes of direct-acting analogue indicating instruments). |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315 uses the same circle-with-letter instrument convention, listing G for galvanometer alongside A, V and W; ANSI C39.1 covers electrical analogue indicating instrument requirements. |
| Key difference | There is no meaningful drawing difference — both standards use a circle with the letter G. The main caution in both systems is contextual: 'G' in a circle can also denote a generator, so IEC drawings often qualify sources with additional marks (e.g. G with a sine wave for an AC generator), leaving the plain G-in-circle in a measurement branch to read as galvanometer. |
Terminals / pins
| Pin | Name |
|---|---|
| pos | + |
| neg | - |
Typical values
Typical educational moving-coil galvanometers deflect full-scale at 50 µA to 1 mA with coil resistances of roughly 20–200 Ω; sensitive laboratory and mirror galvanometers historically resolved nanoamps. Centre-zero types read ±50 µA to ±35 mA. Converting a 50 µA, 100 Ω movement to a 1 A ammeter needs a shunt of about 0.005 Ω; converting it to a 10 V voltmeter needs a series multiplier of about 200 kΩ. Modern laser-scanning 'galvos' (a derived use of the same movement) position mirrors at kilohertz rates.
Where the Galvanometer symbol is used
- GCSE, A-level and class 10–12 physics practicals detecting current direction and magnitude in electromagnetic-induction experiments
- Wheatstone bridge circuits as the null detector between the bridge midpoints
- Potentiometer (slide-wire) experiments for comparing EMFs at zero-current balance
- Teaching conversion of a basic meter movement into an ammeter (parallel shunt) or voltmeter (series multiplier)
- Tangent galvanometer demonstrations relating coil current to Earth's magnetic field
- Analogue panel-meter movements and laser-show/LiDAR scanning galvos derived from the same moving-coil principle
Example
In a Wheatstone bridge diagram, the Galvanometer symbol bridges the two midpoint nodes: its + pin connects to the junction of the known resistor arms and its − pin to the junction of the unknown-resistor arm, and the variable arm is adjusted until the needle shows zero deflection — at null, no current flows through the galvanometer and the unknown resistance equals R2×R3/R1.
Key facts
- The symbol is a circle containing the letter G, following the same instrument convention as A (ammeter) and V (voltmeter) in IEC 60617 and ANSI/IEEE 315.
- A galvanometer detects small currents — typically 50 µA to 1 mA full-scale — and centre-zero types indicate current direction as well as magnitude, which is why the terminals are marked + and −.
- It is the null detector in Wheatstone bridge and potentiometer measurements: the circuit is balanced until the galvanometer reads exactly zero.
- Adding a low-resistance shunt in parallel converts a galvanometer into an ammeter; adding a high-resistance multiplier in series converts it into a voltmeter.
- The movement is the D'Arsonval moving-coil mechanism: torque proportional to current, restrained by a hairspring, giving a linear scale.
- Never connect a galvanometer directly across a supply — its full-scale current is microamps and its coil resistance low, so it will be destroyed.
- In a circle, 'G' can also mean generator; a galvanometer is identified by its position in a measuring branch and its polarity marks.
- Deflection direction reverses when current reverses — the basis of induction demonstrations where pushing a magnet into a coil kicks the needle one way and withdrawing it kicks it the other.
Frequently asked questions
How do you draw the galvanometer symbol in a physics circuit diagram?
Draw a circle with a capital letter G inside it and one connection wire on each side — the same pattern as the ammeter (circle-A) and voltmeter (circle-V) symbols. Some textbooks add a small needle or an arrow through the circle. For class 10–12 and A-level answers, connect it in series in the branch whose current you are detecting (like an ammeter), or between the bridge midpoints in a Wheatstone bridge.
What is the difference between a galvanometer and an ammeter?
Both measure current, but a galvanometer is a bare, highly sensitive movement (microamp full-scale, often centre-zero to show direction) used to detect small currents, while an ammeter is that same movement fitted with a calibrated low-resistance shunt so it can read practical currents in amps. In symbols: circle-G versus circle-A. Every classic analogue ammeter contains a galvanometer at its heart.
How do you convert a galvanometer into an ammeter or voltmeter?
For an ammeter, connect a low-value shunt resistor in parallel so most of the load current bypasses the coil: S = Ig×G/(I − Ig), where Ig is full-scale coil current, G coil resistance and I the desired range. For a voltmeter, connect a high-value multiplier resistor in series: R = V/Ig − G. Example: a 50 µA, 100 Ω movement becomes a 10 V voltmeter with a series resistance of about 199.9 kΩ.
Why is a galvanometer used in a Wheatstone bridge instead of an ammeter?
The bridge method measures resistance by finding the exact balance point where zero current flows between the midpoints. Detecting that null needs maximum sensitivity near zero, not a wide measuring range — a galvanometer deflecting visibly for a microamp of imbalance locates balance far more precisely than an ammeter whose scale starts at milliamps. At null the galvanometer draws no current, so its own resistance doesn't affect the result.
Does a galvanometer have polarity?
Yes. The needle deflects one way for current entering the + terminal and the other way for reversed current. Centre-zero galvanometers exploit this to show current direction — the classic electromagnetic-induction demonstration. Pivoted-left (zero-left) types can be damaged by hard reverse deflection, so the + and − pins on the symbol should be respected when the current direction is known.
Related symbols
- Ammeter symbol
- Battery symbol
- Current Source symbol
- Resistor symbol
- Voltmeter symbol
- Wheatstone Bridge symbol
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