The properties of a diode are different, depending on the direction of p.d. across it.
An appropriate range of p.d. includes 0 V and the maximum voltage of the diode and at least four other readings.
An appropriate range for a diode includes the maximum p.d. in both directions, with positive and negative values.
For electricity investigations, it is good practice to take many more than the minimum number of measurements.

Keywords

Diode - an electrical component that is used to prevent current flow in one direction
Semiconductor - a material that has both metallic and non-metallic properties
Threshold p.d. - the potential difference at which a diode allows current to flow
Reverse–biased - when a diode is reverse–biased, it prevents current from flowing
Forward–biased - when a diode is forward–biased, it allows current to flow

Common misconception

The gradient of an I–V graph is equal to 1/R because I = V ÷ R.

Explain how the equation for a straight line graph y = mx + c does not apply in this case because the graph is not a straight line.

Limit the voltage of the supply to less than 3 V and use a milliammeter to measure the current. A 100 kiloohm resistor may be added in series to prevent the fuse in the milliammeter blowing.

Teacher tip

Equipment

diodes, milliammeters, voltmeters, variable resistors, 100 kiloohm resistors, electrical leads

Content guidance

Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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Starter quiz

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6 Questions

Q1.

What happens when free electrons in a metal collide with metal ions?

the metal ions vibrate less vigorously

the metal ions vibrate as before

Correct answer: the metal ions vibrate more vigorously

Q2.

What causes free electrons in a metal to move?

a resistance

a current

Correct answer: a p.d.

Q3.

Which of the following effects will result from a higher p.d. across a metal wire in a working electrical circuit?

Correct answer: its free electrons will move faster

Correct answer: a higher current will flow through it

the metal will become cooler

the metal ions will vibrate less vigorously

Q4.

Which of the followings statements about resistors A and B is correct?

resistor A has a higher resistance than resistor B

Correct answer: resistor A has a lower resistance than resistor B

both resistors have the same resistance

it is not possible to say which resistor has the higher resistance

Q5.

Which of the following elements is a semiconductor?

iron

copper

aluminium

Correct answer: silicon

Q6.

Which of the following statements about the I–V graph shown is correct?

as the p.d. increases, the resistance increases

Correct answer: as the p.d. increases, the resistance decreases

the resistance remains the same as the p.d. changes

it is not possible to say if the resistance changes

Exit quiz

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6 Questions

Q1.

Which of the following components are shown in the image?

resistors

capacitors

thermistors

Correct answer: diodes

Q2.

Which of the following statements about the ends of a diode is correct?

there are two positive ends

there are two negative ends

Correct answer: there is one positive and one negative end

both ends are neutral

Q3.

Which of the following are the main chemical elements that can be used to make diodes?

copper

aluminium

Correct answer: silicon

Correct answer: germanium

Q4.

What type of voltmeter is needed to measure the potential difference (p.d.) across a diode: one that measures in volts (V), millivolts (mV), or kilovolts (kV)?

Correct answer: one that measures in millivolts (mV)

one that measures in volts (V)

one that measures in kilovolts (kV)

Q5.

When the positive end of a diode is connected to the positive terminal of a battery and the negative end of the diode is connected to the negative terminal of the battery, the diode is ...

Correct answer: in forward bias.

in reverse bias.

at the threshold p.d.

overloaded.

Q6.

Which of the following occurs when the p.d. across a forward–biased diode is increased to just above the threshold p.d.?

Correct answer: the current increases

the resistance increases

the current stops flowing

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