Current-Voltage (I-V) characteristics for components

The relationship between current through, and voltage across, a component is called the current-voltage (I-V) characteristic.

Resistor at constant temperature

For a fixed resistor, the voltage is directly proportional to the current. Doubling the amount of energy into the resistor results in a current twice as fast through the resistor. This relationship is called Ohm's Law and is true because the resistance of the resistor is fixed (because the temperature does not change).

curriculum-key-fact
A resistor is an ohmic conductor
Circuit with a battery, resistor, variable resistor, diode, ammeter and a voltmeter connected in parallel to the diode.Circuit with a battery, resistor, variable resistor, diode, ammeter and a voltmeter connected in parallel to the diodeGraph plotting potential difference against current for a fixed resistor. Line is directly proportional.Graph plotting potential difference against current for a fixed resistor. Line is directly proportional

Filament Lamp

In a filament bulb, the current does not increase at the same rate as the voltage. Doubling the amount of energy does not cause a current twice as fast.

The more energy that is put into the bulb, the harder it is for the current to flow – the resistance of the bulb increases. As the voltage increases, so does the temperature of the thin wire inside the bulb, the filament. The increased vibrations of the ions in the filament because of the increased temperature, make it harder for the electrons to get past.

Circuit with a battery, variable resistor, lamp, ammeter and a voltmeter connected in parallel to the lamp.Circuit with a battery, variable resistor, lamp, ammeter and a voltmeter connected in parallel to the lampGraph plotting potential difference against current for a filament bulb. Line is an upward curve, that levels out and start to dip and potential difference increase.Graph plotting potential difference against current for a filament bulb. Line is an upward curve that levels out and starts to dip as potential difference increases

Diode

A semiconductor diode only allows current to flow in one direction. If the potential difference is arranged to try and push the current the wrong way (also called reverse-bias) no current will flow as the diode's resistance remains very large. Current will only flow if the diode is forward-biased.

When forward-biased, the diode's resistance is very large at low potential differences, usually up to about 0.7 V, but at higher potential differences, the resistance quickly drops and current begins to flow.

Circuit with a battery, variable resistor, resistor, ammeter and a voltmeter connected in parallel to the resistor.Circuit with a battery, variable resistor, resistor, ammeter and a voltmeter connected in parallel to the resistorGraph plotting potential difference against current for a diode. Line is horizontal on the x-axis for a part, and then it curves upwards sharply.Graph plotting potential difference against current for a diode. Line is horizontal on the x-axis for a part, and then it curves upwards sharply

Variation of resistance in a thermistor and an LDR

The resistance of a thermistor varies with temperature. As the temperature increases the resistance decreases.

The resistance of an LDR (Light Dependent Resistor) varies with light intensity. The more light incident on the LDR the smaller the resistance of it.