An ammeter is a device that measures the amount of current flowing through an electrical circuit. The ammeter must have a low resistance so that the current travelling through it remains unaffected. To measure the circuit current, an ammeter is connected in series.

An instrument called a galvanometer is used to find weak electric currents in a circuit. Although the galvanometer itself has a tiny current-carrying capability, the galvanometer coil has a moderate resistance of roughly 100 ohms (1 mA).

Only little currents may be detected by a galvanometer. As a result, it is transformed into an ammeter to measure enormous currents. By joining a low resistance known as a shunt resistance in parallel to the galvanometer, it may be transformed into an ammeter.

If 𝐺 is the galvanometer’s resistance and 𝐼𝑔 is its full-scale deflection current, then the shunt resistance needed to transform galvanometer into an ammeter with a range of 0 to 𝐼 ampere is, $$S=\frac{I_g \times G}{I-I_g}$$

𝐼𝑔 is calculated using the equation, 𝐼𝑔 = 𝑁𝑘, where 𝑁 is the number of divisions on the galvanometer and 𝑘 is the figure of merit of galvanometer.

Let 𝑙 be the length of the resistance wire required for a resistance of 𝑆 ohm, $$l=\frac{\pi r^2 S}{\rho}$$

where, 𝑟 is the radius of the wire and 𝜌 is the resistivity of the material of the wire.

Requirements for this Science Experiment

⦁ Galvanometer ⦁ Ammeter ⦁ Rheostat ⦁ Battery Eliminator ⦁ Plug Key