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Form 4 Physics Questions and Answers on Thin Lenses

In this session, we are going to solve Form 4 Physics questions on thin lenses. Answers are in video format.

Lessons (18)

• 1.    An object placed in front of a convex lens of focal length 10cm produces an image at a distance of 15cm from the lens and on the same side as the object. Determine the position of the object.
  2m 57s

• 2.    (a) Draw a ray diagram to show how a convex lens works as a magnifying glass. (b) The diagram in figure 3 shows a certain eye defect. (i) Name the defect. (ii) Draw on the same diagram an arrangement to correct the defect.
  7m 52s

• 3.    Fig. 8 shows an object O placed in front of a concave lens with principal foci F and F’. Construct a ray diagram to locate the position of the image.
  3m 55s

• 4.    Fig. 2 drawn to scale, shows a lens L1 placed 30cm from an object O. The image is formed on the screen S 50cm from the lens. On the figure, draw appropriate rays then determine the focal length of the lens.
  3m 24s

• 5.    Sketch a diagram to show the position of an object, when a converging lens is used as a magnifying glass.
  6m 20s

• 6.    Figure 21 shows a converging lens whose focal point F is marked. An object is placed in front of the lens such that a real magnified image is formed by the lens. Sketch on the same diagram, a ray diagram to represent this.
  4m 8s

• 7.    Figure 13 represents an object O placed 10cm in front of a diverging lens. F is the focal point of the lens. Draw rays to locate the position of the image. Determine the image distance.
  4m 10s

• 8.    Figure 10 (drawn to scale) shows an image L formed by a diverging lens, L. On the same diagram, draw appropriate rays to locate the position of object. Determine the object distance.
  4m 22s

• 9.    (a) Figure 8 shows an experimental set-up consisting of a mounted lens L, a screen S, a meter rule and a candle. (i) Describe how the set-up may be used to determine the focal length, f, of the lens. (ii) State the reason why the set-up would not work if the lens were replaced with a diverging lens (b) The graph in figure 9 shows the relationship between #1/u# and #1/v# for a converging lens where
  8m 53s

• 10.    A vertical object is placed at the focal point F of a diverging lens as shown in figure 16. Sketch a ray diagram to show the image of the object.
  3m 13s

• 11.    An illustrated vertical object is initially placed on the principal axis of a converging lens and 32cm from it. The focal length of the lens is 15cm. The object is now placed at a point 12cm from the lens and on the same side. State two changes other than magnification that are observed on the image formed due to this change.
  3m 27s

• 12.    A vertical object is placed 20cm in front of a convex lens of focal length 5cm. (i) Determine: (I) The image Distance (II) The magnification. (ii) State two characteristics of the image.
  3m 33s

• 13.    State what it is meant by the term accommodation as applied to the human eye
  0m 57s

• 14.    (a) Figures 11 (a) and (b) show diagrams of the human eye. (i) Sketch in figure 11 (a) a ray diagram to show short sightedness. (ii) Sketch in figure 11 (b) a ray diagram to show how lens can be used to correct the short sightedness. (b) Figure 12 shows the features of a simple camera. (i) Name the parts labeled A and B. (ii) A still object is placed at a certain distance from the camera. Explain
  11m 51s

• 15.    The diagram in figure 2 shows an object O laced in front of a converging lens. F and F’ are the principal foci for the lens. The object is now moved along the principal axis until a virtual image is produced. On the same diagram: (i) Draw the object O in the new position along the principal axis. (ii) Sketch rays to show formation of the virtual image.
  5m 17s

• 16.    Figure 7 shows how rays from a distant and a near object are focused inside a human eye with a certain defect. Name the defect and state the cause of this defect.
  1m 59s

• 17.    In an experiment, a pin, a converging lens and a plane mirror are arranged as shown in figure 4. The distance between the pin and the plane mirror is L cm while the distance between the lens and the plane mirror is q cm. The position of the pin is adjusted until its tip coincides with its real image. State the focal length of the lens.
  2m 32s

• 18.    (a) State the meaning of the term “principal focus” as applied in lenses. (b) You are provided with the following apparatus to determine the focal length of a lens; A biconvex lens and lens holder, a lit candle, a white screen, a meter rule. (i) Draw a diagram to show how you would arrange the above apparatus to determine the focal length of the lens (ii) Describe the procedure you would follow.
  7m 19s