Measuring amps & volts

You need to know how to measure current and voltage.

Current

Current is a measure of how much electric charge flows through a circuit. The more charge that flows, the bigger the current.

Current is measured in units called amps. The symbol for amps is A. For example, 20A is a bigger current than 5A.

Measuring current

A device called an ammeter is used to measure current. Some types of ammeter have a pointer on a dial, but most have a digital readout. To measure the current flowing through a component in a circuit, you must connect the ammeter in series with it.

Two circuits, both with a cell, an ammeter, and a lamp. In the first, the ammeter is connected before the lamp. In the second, the ammeter is connected after the lamp

Voltage

Voltage is a measure of the difference in electrical energy between two parts of a circuit. The bigger the difference in energy, the bigger the voltage.

Voltage is measured in volts. The symbol for volts is V. For example, 230V is a bigger voltage than 12V.

Measuring voltage

Voltage is meaured using a voltmeter. Some types of voltmeter have a pointer on a dial, but most have a digital readout. To measure the voltage across a component in a circuit, you must connect the voltmeter in parallel with it.

Shows a circuit with a cell, a lamp, and a voltmeter. The voltmeter is connected in parallel to the lamp

Using a voltmeter to measure the voltage across a lamp

You can measure the voltage across a cell or battery. The more cells, the bigger the voltage.

One circuit has a voltage of 1.5V. A lamp and a voltmeter are connected. The other circuit has a voltage of 4.5V. It has a lamp and a voltmeter connected

The more cells, the bigger the voltage

Checkpoint

Current Voltage
Measured in amps, A volts, V
Measured with ammeter in series voltmeter in parallel
Circuit symbol of measuring devise A circle with an A in it A circle with a V in it

Current in series circuits

The current is the same everywhere in a series circuit. It does not matter where you put the ammeter, it will give you the same reading.

The circuit has a cell, ammeter 1 reading 0.5A, a lamp, ammeter 2 reading 0.5A, another lamp, ammeter 3 reading 0.5A

All three ammeters give the same reading in this series circuit

Adding more cells

The current in a series circuit depends upon the number of cells. The more cells you add, the greater the current.

The first circuit has one cell, an ammeter reading 0.5A and a lamp. The second circuit has two cells, an ammeter reading 1.0A, and a lamp. The third circuit has three cells, an ammeter reading 1.5A and a lamp.

The more cells, the greater the current

Current is not used up

You might think that the current gets less as it flows through one component after another. But it is not like this. The current is not used up by the components in a circuit. This means that the current is the same everywhere in a series circuit, even if it has lots of lamps or other components.

Circuit is two cells, an ammeter reading 0.3A, a lamp, a second ammeter reading 0.3A, another lamp, a third ammeter reading 0.3A, another lamp, and a fourth ammeter reading 0.3A

The current is the same everywhere in a series circuit



Test

1. What is wrong with this circuit diagram?

circuit shows a cell, a lamp, and an ammeter. The ammeter is connected in parallel.

2.

Which ammeter will have the biggest reading?

A series circuit powered by a battery, consisting of an ammeter (ammeter 1), a lamp, a second ammeter (ammeter 2) and another lamp.

Última modificación: martes, 19 de julio de 2016, 15:17