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3.2.3a Converging and diverging lenses

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Question 14

An IGCSE student is determining the focal length of a lens.

The student records two sets of readings for the object distance xxx (the actual distance from the illuminated object to the centre of the lens) and the image distance yyy (the actual distance from the centre of the lens to the screen).

For the first set of readings, the student makes measurements on a scale diagram of the experimental set-up. The diagram is drawn to 14\frac{1}{4}41​ (one-quarter) of the actual size. On this diagram:

  • The measured distance from the illuminated object to the lens is u=4.5 cmu = 4.5\text{ cm}u=4.5 cm
  • The measured distance from the lens to the screen is v=9.0 cmv = 9.0\text{ cm}v=9.0 cm

For the second set of readings, the student records the actual distances directly in the laboratory:

  • x=55.0 cmx = 55.0\text{ cm}x=55.0 cm
  • y=15.5 cmy = 15.5\text{ cm}y=15.5 cm
a.

Calculate the actual distance xxx and the actual distance yyy for the first set of readings.

[2]
b.

Calculate the focal length fff of the lens for both sets of readings using the equation:

f=xyx+y f = \frac{xy}{x + y} f=x+yxy​

Record your values of fff to an appropriate number of significant figures (at least 3 significant figures).

[4]
c.

Calculate the average value of the focal length of the lens.

[2]
d.

State two precautions you would take in the laboratory in order to obtain reliable measurements.

[2]
Markscheme

3.2.3a Converging and diverging lenses Questions

  1. IGCSE
  2. /Physics
  3. /3.2.3a Converging and diverging lenses

56 exam-style questions on CIE IGCSE Physics 3.2.3a Converging and diverging lenses. Each one has a worked solution and a mark scheme showing where the marks go.

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