Image formation and magnificationEdexcel A-Level Physics: Subtopic test

1. 1
   A slide projector uses a thin converging lens of focal length 0.100 m. A slide, 24 mm wide, is placed 0.120 m from the lens on the principal axis, and a sharp image is formed on a distant screen.

   (a)

   What is the distance from the lens to the screen?

   [1 mark]

   • A0.055 m
   • B0.22 m
   • C0.020 m
   • D0.60 m

   (b)

   What is the magnification produced by the projector?

   [1 mark]

   • A5.0
   • B0.20
   • C0.60
   • D6.0

   (c)

   Calculate the width of the image on the screen.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student uses a thin converging lens of focal length 0.060 m as a magnifying glass. She holds an insect specimen 2.0 mm long on the principal axis, 0.045 m from the lens, and views it through the lens from the other side.

   (a)

   In the real-is-positive convention, what is the sign of the image distance v here, and why?

   [1 mark]

   • APositive, because the image is on the far side of the lens
   • BNegative, because the refracted rays diverge and the image is virtual
   • CNegative, because the image is inverted
   • DPositive, because the image is magnified

   (b)

   What is the distance of the image from the lens?

   [1 mark]

   • A0.026 m
   • B0.015 m
   • C0.18 m
   • D0.105 m

   (c)

   Calculate the length of the image of the specimen.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A camera lens of focal length 0.050 m is used to photograph a person who is 1.80 m tall and standing 4.0 m from the lens. The light-sensitive sensor is placed behind the lens at the position where a sharp image forms.

   (a)

   Calculate the distance from the lens to the sensor.

   [3 marks]

   (b)

   Calculate the height of the image of the person on the sensor. The person then walks closer to the camera. Explain how the lens-to-sensor distance must change for the image to stay sharp.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student investigates image formation with a thin converging lens of focal length 0.15 m. An illuminated object 2.0 cm tall is placed on the principal axis and a white screen is moved until a sharp image is seen. She records the object distance u and image distance v for several positions and plots a graph of 1/v against 1/u.

   (a)

   Explain how the student can use the graph to determine the focal length of the lens, including why the graph is a straight line and what its gradient and intercepts should be.

   [6 marks]

   (b)

   The student places the object 0.25 m from the lens. Determine the image distance, the magnification and the height of the image. She then moves the object to 0.10 m from the lens. Explain, with calculation, why the image can no longer be seen on the screen and state how its size compares with the object.

   [6 marks]

   Total for question 4: 12 marks

End of questions