Question Video: Identifying the Shunt of a Hot-Wire Ammeter | Nagwa Question Video: Identifying the Shunt of a Hot-Wire Ammeter | Nagwa

# Question Video: Identifying the Shunt of a Hot-Wire Ammeter Physics • Third Year of Secondary School

The diagram shows a hot-wire ammeter. Which of the components shown in the diagram includes a shunt?

02:22

### Video Transcript

The diagram shows a hot-wire ammeter. Which of the components shown in the diagram includes a shunt?

In this question, we’re asked to identify the shunt in a hot-wire ammeter. First, let’s remind ourselves how a hot-wire ammeter works.

A hot-wire ammeter is a device used to measure an alternating electrical current. In this diagram, we have a circuit consisting of an alternating-current source and a resistor. We also have an ammeter. The ammeter is designed so that the current in the circuit is split across two parallel branches. One of these branches contains a resistor, called a shunt resistor. The other branch does not contain any components. But it does contain a section of wire that is made out of a special material, platinum–iridium alloy. This is referred to as a hot wire.

A piece of string, which does not conduct electricity, is tied to the hot wire. The string runs across a pulley and is tied to a spring at the other end. The spring holds the string taut, so that it pulls on the hot wire. When the alternating current in the circuit reaches the ammeter, the charges either flow through the branch that contains the shunt resistor or through the branch with the hot wire.

When charge flows through the hot wire, the temperature of the hot wire increases, and the wire expands, becoming longer. When the hot wire becomes longer, the spring is able to pull the nonconducting string towards the right. As the string moves over the pulley, it changes the position of a needle, which points to a measurement scale. This allows the value of the alternating current in the circuit to be measured.

Now we know how a hot-wire ammeter works, identifying the shunt in this diagram will be fairly simple. Let’s go through each of the components labeled.

Component I consists of some wire and a resistor. This is connected in parallel to the wire in component II. Component II must be the hot wire; we can see it is being pulled on by the nonconducting string, component III, which is connected to a spring, component IV.

To answer this question, we simply need to recall that the term “shunt” is short for shunt resistor. The shunt resistor in this diagram would be located in component I of the diagram. This resistor is also connected in parallel to the hot wire, which is exactly how a shunt should be connected. So, we can be confident that this resistor is the shunt. The answer to this question is, therefore, component I.

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