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Ohm’s law, electric power and energy - CCEAOhm's law and resistance

Ohm’s Law states that the voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions, such as temperature, remain constant.

Part of Physics (Single Science)Electricity

Ohm's law and resistance

All conductors show some opposition to electric current.

This opposition to current is called resistance.

A good conductor has low resistance.

A poor conductor, or insulator, has high resistance.

The two main ways of increasing the current in an electrical circuit are by increasing the voltage or by decreasing the resistance.

Changing the voltage

If you increase the voltage across a component, there will be more current in the component.

Too high a voltage and the lamp will break.

Three circuits. Number 1 has a cell at the top, an ammeter reading 0.1A on the right and a lamp giving off a little light at the bottom. Number 2 has a battery at the top, an ammeter reading 0.2A on the right and a lamp giving off a lot of light at the bottom. Number 3 has two batteries at the top, an ammeter reading 0.3A at the right and a blown bulb at the bottom.
Three series circuits with increasing voltage

Changing the resistance

If you increase the number of lamps in a series circuit, there will be less current.

The lamps resist the current, so if you put more lamps into the circuit, there is more resistance.

Two circuits. Number 1 has a cell and closed switch on the top, an ammeter reading 0.4A at the right and a brightly lit bulb at the bottom. Number 2 also has a cell and closed switch at the top, an ammeter reading 0.2A at the right and two dimly lit bulbs at the bottom.
Two series circuits, one with one lamp, the other with two lamps

You could increase or decrease the resistance in a circuit by using a variable resistor (also known as a rheostat).

Three circuits. Number 1 has a cell at the top, an ammeter reading 0.2A on the right and a lamp giving off a little light at the bottom right and a variable resistor bottom left. Number 2 has a cell at the top, an ammeter reading 0.4A on the right and a lamp giving off a medium amount of light at the bottom right and a variable resistor at bottom left. Number 3 has a cell at the top, an ammeter reading 0.5A on the right and a lamp giving off a lot of light at the bottom right and a variable resistor at bottom left.
Three series circuits, all containing a cell, ammeter, lamp and variable resistor
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Prescribed practical 7 - Section 1

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