What Is a Galvanometer? Working Principle, Diagram & Uses

A galvanometer is one of the first sensitive instruments every physics student meets — and one of the most misunderstood. This guide explains what it is, how it works, how to read its diagram, and how to use it correctly in the lab, in clear exam-ready language for CBSE and ICSE students.

Key facts at a glance

• Type: Most laboratory galvanometers are moving-coil (pivoted) galvanometers.
• Function: Detects and measures currents as small as a few microamperes.
• Principle: A current-carrying coil in a magnetic field experiences a torque.
• Key relation: Deflection is directly proportional to current — θ ∝ I.
• Reads: Both sides of a central zero, so it shows current direction.
• Becomes an ammeter with a low resistance (shunt) in parallel; a voltmeter with a high resistance in series.

What is a galvanometer?

A galvanometer is an instrument that detects and measures very small electric currents in a circuit. When a small current flows through it, a pointer deflects across a scale. The size of the deflection shows the magnitude of the current, and the direction of deflection shows its direction. Because the needle swings either side of a central zero, the galvanometer is the basis for both the ammeter and the voltmeter you use later in the syllabus.

Working principle of a galvanometer

A galvanometer works on the principle that a current-carrying coil placed in a magnetic field experiences a torque. In a moving-coil galvanometer, a rectangular coil sits between the poles of a permanent magnet. When current passes through the coil, each side experiences a force (Fleming’s left-hand rule), and together these form a couple that rotates the coil. A spring provides a restoring torque, so the coil — and the attached needle — settles where the two torques balance.

The deflection θ is directly proportional to the current I:

θ ∝ I  ⇒  I = (k / NAB) × θ

where N = number of turns, A = coil area, B = magnetic field strength, and k = the spring constant. A radial magnetic field is used so the scale stays linear and evenly divided.

Parts of a galvanometer

The main components of a moving-coil galvanometer are:

• Coil — carries the current and rotates in the magnetic field.
• Permanent magnet — provides the magnetic field.
• Soft-iron core — makes the field radial, giving a linear scale.
• Spring — provides the restoring torque and carries current to the coil.
• Pointer and scale — show the deflection, which is the reading.

How to use a galvanometer in the lab

Follow these steps for a correct, safe reading:

• 1. Check the zero. With no current flowing, the needle should rest on the central zero. Adjust the zero corrector if it does not.
• 2. Connect in series. A galvanometer goes in series with the branch whose current you want to detect — never alone across a cell.
• 3. Protect the coil. Always include a high resistance or a known shunt so a sudden large current cannot burn out the delicate coil.
• 4. Close the circuit briefly. Tap the key, observe the direction of deflection, then take the steady reading.
• 5. Read the deflection. Count the divisions. If the needle moves the wrong way, reverse the connections — that also tells you the current’s direction.

Galvanometer vs ammeter vs voltmeter

This is one of the most-asked exam questions. All three instruments begin from the same galvanometer; the difference is what you add to it. A galvanometer measures very small currents and direction. Add a low resistance (shunt) in parallel and it becomes an ammeter for larger currents. Add a high resistance in series and it becomes a voltmeter for potential difference.

Frequently asked questions

What is a galvanometer used for?
To detect and measure very small electric currents and to check the direction of current flow. It is also the basis for ammeters and voltmeters.

Why is a galvanometer connected in series?
Because it detects the current flowing through a branch, the same current must pass through its coil — which requires a series connection.

Can a galvanometer measure voltage?
Not on its own. Add a high resistance in series and it becomes a voltmeter that reads potential difference.