Let's understand the role of a shunt in a moving-coil instrument.

Moving-Coil Instrument Shunt Explanation

A moving-coil instrument, like a galvanometer, is often used as the basis for ammeters and voltmeters. A galvanometer can only handle a small amount of current. To measure larger currents, a special resistance is connected across its terminals. This resistance is called a shunt.

Purpose of a Shunt

The main purpose of a shunt in an ammeter (which uses a moving-coil galvanometer) is to increase its current measuring range. It provides an alternative path for the majority of the current, allowing only a small, proportional fraction to pass through the delicate moving coil.

Shunt Resistance and Connection

• To effectively bypass most of the current, the resistance of the shunt must be much lower than the resistance of the moving coil itself. If the shunt resistance were high, most of the current would still try to flow through the coil, potentially damaging it and not extending the range.
• For the current to be divided between the coil and the shunt, they must be connected in parallel. A parallel connection ensures that the voltage across both the coil and the shunt is the same, and the total current divides between them according to their resistances (lower resistance takes more current).

If the shunt were connected in series, it would simply add to the coil's resistance, increasing the overall resistance of the ammeter and reducing the current through the circuit being measured, which is not the desired function.

Therefore, in a moving-coil instrument used as an ammeter, a low resistance is connected in parallel with the coil to serve as a shunt.

Based on this understanding, let's look at the options:

• High resistance, series connection: Incorrect. A shunt is low resistance and connected in parallel.
• High resistance, parallel connection: Incorrect. A shunt is low resistance.
• Low resistance, parallel connection: Correct. This matches the requirement for a shunt.
• Low resistance, series connection: Incorrect. A shunt is connected in parallel.

The correct choice identifies the shunt as a low resistance connected in parallel with the coil.