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New
New
Year 10
OCR
Foundation

Measuring the resistance of a diode

I can interpret an I–V graph of a diode in order to describe its properties.

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New
New
Year 10
OCR
Foundation

Measuring the resistance of a diode

I can interpret an I–V graph of a diode in order to describe its properties.

Download all resources
Share activities with pupils

Lesson details

Key learning points

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

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.

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

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?
An image in a quiz
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?
An image in a quiz
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?
An image in a quiz
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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