The two main ways of increasing the current in an electrical circuit are by increasing the voltage or by decreasing the resistance.
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.
You could increase or decrease the resistance in a circuit by using a variable resistor.
The quantities voltage, current and resistance are linked by the relationship:
This relationship is called Ohm's Law. We usually write Ohm's Law as;
The symbol for resistance is R, it is measured in ohms .
The symbol for voltage is V, it is measured in volts .
The symbol for current is I, it is measured in amperes .
Make sure that if there is more than one voltage or current in a problem, you use the voltage across the resistor and the current through it, not just any values that you see in the question.
When a resistor is kept at a constant temperature, its resistance will remain unchanged. We can confirm this experimentally by connecting a resistor to a power supply and measuring the current in the resistor as the supply voltage is increased.
Plotting voltage (potential difference) against current for the resistor will produce a straight-line graph that passes through the origin.
Calculate the reading on the ammeter in the circuit shown
A change in temperature can cause a change in resistance for some materials. These materials are known as non-ohmic conductors.
For example, a thermistor’s resistance depends on its temperature.
A voltage-current graph for a thermistor is not a straight line.
This means that the resistance of the thermistor is not constant for different values of current. When the current decreases, the resistance of the thermistor increases.