An ammeter measures the current in an electrical circuit. The standard unit of current is the ampere, although a 12V ammeter may be able to measure current in milliamps. The milliamp is a more useful unit for home experiments because of the low amount of current used in these projects. A 12V ammeter is a commonly used instrument, and this function may be performed by a multimeter, which also measures other electrical quantities. An older ammeter may use a needle that moves in response to an electrical current, while a newer ammeter will register current with a digital display.
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Things you need
- 2 Leads with alligator clips
- Ammeter or multimeter
- Light bulb
Examine the structure of a simple circuit that consists only of a light bulb and a battery. One lead connects the negative terminal of the battery to the negative terminal of the light bulb. The other lead connects the positive terminal of the light bulb to the positive terminal of the battery.
Study the inputs for your 12V ammeter. A dedicated 12V ammeter will probably only have one input and one output. However, a multimeter should have a dedicated input for measuring current. This is because the multimeter must be part of the circuit when measuring current, unlike other electrical quantities such as voltage and resistance.
Select the type of current you wish to measure. Most 12V ammeters have a setting for direct current (DC) and alternating current (AC). For a circuit that uses a battery as a power source, you'll select DC.
Turn your 12V ammeter on and set it for the highest range of current that it allows. Disconnect the positive lead from the light bulb and touch the probe from the 12V ammeter's input (A) to the free end of the positive lead from the battery. Touch the probe from the 12V ammeter's negative terminal to the light bulb's positive terminal.
Select progressively lower current ranges on your 12V ammeter until the needle moves or the 12V ammeter displays a result. This will prevent damage to the ammeter by overloading it with excessive current.
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