Lesson Explainer: Ammeters | Nagwa Lesson Explainer: Ammeters | Nagwa

Lesson Explainer: Ammeters Science

In this explainer, we will learn how to use ammeters in electric circuits to measure the current through a component in the circuit.

Recall that electric current is the flow of electric charge.

We can measure the electric current at a point in an electric circuit using a device called an ammeter.

The circuit symbol for an ammeter is a circle with the letter A in the middle of it, as shown below.

Example 1: Finding the Number of Ammeters in a Circuit

The diagram shows an electric circuit. How many ammeters are there in the circuit?

Answer

The circuit symbol for an ammeter is a circle with the letter A in the middle of it, as shown below.

There are 2 of these symbols in the circuit diagram we have been given; therefore, there are 2 ammeters in the circuit.

There are several other symbols in the circuit diagram. What each of these symbols represents is shown below.

Example 2: Describing the Function of an Ammeter

What quantity does an ammeter measure?

Answer

In this question, we must write a short description of what an ammeter measures. We must write a description that is clear and simple; we do not want to use more words than we really need to.

We can write that an ammeter measures electric current.

In order to use an ammeter to measure the current at a point in an circuit, we must connect it to the circuit in a certain way.

Consider the circuit shown in the diagram below.

This circuit consists of a bulb connected to a cell using wires.

Charge flows from one terminal of the cell, along a piece of wire, through the bulb, along another piece of wire, finally ending up at the other terminal of the cell. This is the only path that charge can follow as it moves around the circuit. This path is shown in blue below.

In order to measure the current through a component in a circuit, an ammeter must be placed on the same path as the current. So, for this circuit, in order to measure the current through the bulb, we must place the ammeter somewhere along the blue path. We have two choices, as shown below.

Either choice will give us the same value for the current through the bulb.

When circuit components are connected along the same path, one after another, like this, we say that they are connected in series. In order to measure the current through a component, an ammeter must be connected in series with that component.

Rule: Using Ammeters in Circuits

In order to measure the current through a component in a circuit, an ammeter must be connected in series with that component.

Now consider the circuit shown below.

Charge flows from one terminal of the cell, along a piece of wire, but then the path splits. The charge can either go one way, passing through the bulb, or the other, passing through the ammeter. This is shown below. The blue path splits into the red and green paths. The red and green paths then join together again into the blue path.

The ammeter is now on a different path from the bulb, so it cannot measure the current through the bulb.

When circuit components are on different paths of the circuit like this, we say that they are connected in parallel.

Example 3: Recognizing When an Ammeter Is Connected Correctly

Each of the following diagrams shows an electric circuit. Which one shows how the ammeter must be connected to the circuit in order to measure the current through the bulb?

Answer

Remember that in order for an ammeter to measure the current through a component, it must be connected in series with it. This means that it must be on the same path of the circuit.

Let’s first consider option A. The different paths of the circuit are shown in different colors below.

The blue path from the cell splits into the green path and the red path. The ammeter is on the green path, and the bulb is on the red path. Therefore, when the ammeter is connected in this way, it cannot measure the current in the bulb.

Now let’s consider option B. There is only one path in the circuit, shown in blue below.

Both the ammeter and the bulb are on the blue path, so the ammeter can measure the current in the bulb.

Let’s also consider option C. The different paths of the circuit are shown in different colors below.

Once again, the blue path from the cell splits into the green path and the red path. The ammeter is on the green path, and the bulb is on the red path. Therefore, when the ammeter is connected in this way, it cannot measure the current in the bulb.

So, the correct answer is B.

Example 4: Describing How to Connect an Ammeter to a Circuit

The diagram shows an electric circuit consisting of a cell and a bulb.

Fill in the blank: In order to measure the current through the bulb, an ammeter must be connected with the bulb.

  1. in series
  2. in parallel

Answer

Remember that in order for an ammeter to measure the current through a component, it must be on the same path of the circuit as that component. Another way of saying this is that it must be in series with that component. So, the answer is A.

Key Points

  • An ammeter is a device that can be used to measure the electric current at a point in a circuit.
  • The circuit symbol for an ammeter is a circle with the letter A in the middle of it, as shown below.
  • Ammeters must be connected in series.

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