Skip to content
Skip to content
Teachers
Go to pupils
New
New

    Measuring the resistance of a diode

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

    New
    New

      Measuring the resistance of a diode

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

      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.

      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 (2026), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

      Lesson video

      Skip lesson video

      Loading...

      Prior knowledge starter quiz

      Download quiz pdf

      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

      Assessment exit quiz

      Download quiz pdf

      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

      Lesson appears in

      UnitCombined science / Circuit components

      AQACombined science

      Show Foundation unit
      Show Higher unit

      EdexcelCombined science

      Show Foundation unit
      Show Higher unit

      OCRCombined science

      Show Foundation unit
      Show Higher unit

      UnitPhysics / Circuit components

      AQAPhysics

      Show Foundation unit
      Show Higher unit

      EdexcelPhysics

      Show Foundation unit
      Show Higher unit

      OCRPhysics

      Show Foundation unit
      Show Higher unit