How do I read an ammeter

Measurements in the circuit

Amperage in the unbranched circuit


We measure the current at different points in the circuit.


Then we see that in an unbranched circuit the current strength is the same at all points.

Amperage in the branched circuit


Again we measure the current at different points in the circuit.


This time the total current I is divided1 at junction 1 on the two light bulbs. It flows together again at junction 2.

Measurements in the circuit

Current measurement

In order to measure the current in an electrical circuit, we need an ammeter. Since the physical quantity current is measured in the unit ampere, we also call the current measuring device ammeter.

How can we measure the current in a circuit?


We measure the current at different points in the circuit. Measurement at different points with an ammeter

In order to be able to measure the current, we have to cut the circuit at one point. We then insert the ammeter there.

At what point do we need to insert the ammeter in the circuit?

It doesn't matter where we put the ammeter in the circuit. Because at every point in the circuit the current has the same strength.

It is important that all electrons flow through the measuring device.

Notice Danger!

You must never connect an ammeter directly to a voltage source. It would break instantly.

In order to be able to easily specify small and large currents, first names have been introduced to the unit amperes.

Units of currents in amperes

Examples of currents

Ammeter, Multimeters

In trade and technology, you have to measure a wide variety of currents, the values ​​of which are often far apart.
Then you have to ask yourself whether you have direct current or alternating current.
For example, the power supply of a television is about 1A.
A transistor device but only about 1 µA.

A measuring device with a measuring range of 1 µA would be destroyed by the 1 A current. So you need different ones ammeter, thats expensive. Therefore were Multimeters developed, these have several switchable measuring ranges in one device. However, in order to be able to measure currents in the order of µA, the measuring device must have an amplifier that amplifies the measuring current. Such measuring devices also have a battery.

We differentiate between dial gauges and those with a digital display.

Advantages of the digital measuring devices are:
- They are cheaper than mechanical measuring devices.
- It's easier to read. That means you don't have to convert the measurement display.
- You can also measure very small currents.
But they also have disadvantages:
- You always need a battery.
- Fluctuating measurands cannot be measured.

Calculate the capacity of batteries

Batteries drive electrons through the circuit. The amount of electron drive (voltage) on each battery is given in volts. Unfortunately, there is no information on the device about how long the battery will last. Why?

Because the greater the current, the faster the battery will be empty.

The service life of a battery can be calculated from the battery capacity. The battery capacity is in Amp-hours (Ah) stated.
1 Ah means that the battery can be operated for 1 hour with 1 A or 10 hours with just 0.1 A.

The following formula applies: operating time = capacity / amperage

Arithmetic exercise

We operate an incandescent lamp (0.3 A) with a 4.5 V flat battery. How long is the battery expected to run out?


The size of electron currents is measured by disconnecting the circuit and switching on an ammeter at the point of separation. The current strength is then read off in amperes (A) on the measuring device. Ampere fractions are often identified by the prefixes m (milli) and µ (micro). The current strength is the same at every point in an unbranched circuit. Therefore it is sufficient to measure them in one place.


Task 1

Explain how large and small currents differ.

exercise 2

Why is the current strength the same at every point in an unbranched circuit?

Task 3

Why can't we talk about electricity consumption when we mean the flow of electrons by electricity?

Task 4

You have a closed circuit made up of a battery and a lightbulb. Describe step by step how to proceed to measure the amperage.

Task 5

Convert to A

Exercise 6

Convert to mA

Exercise 7

Discuss how large the current is in the drawn circuit at points B, C, D and E if a current of 0.75 A is measured at A.

Exercise 8

Why are the same currents not to be expected at the three measuring points in the following figure?

Here you will find a Overview of further articles on the subject of measurements in electric circuits, electromagnets,it also contains links to tasks.

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