## Monday, 8 September 2014

### Optical instruments

Optical instruments

1. Which part of the eye is sensitive to light?

2. (a) What is meant by short sight?
(b) Draw a diagram to show how short sight can be corrected.

3.   The eye can focus at different distances. What is this property called?

4. What is the distance of the near point from the eye for a person with normal vision?

5. Give: (a) two similarities and (b) two differences between the eye and the camera.

6.   A camera lens has a focal length of 50 mm.
How far from the film will it be when the camera takes a photograph of:
(a) a very distant object;
(b)   an object 50 cm from the camera?

7.  What shutter speed would it be suitable to use when taking a photograph of a fast moving car: 1 s, 0.1 s, 10s  or 0.01 s ?

8. A camera with a shutter speed of 0.01 s and with a lens of focal length 50 mm is used to
photograph a car 100 m away moving at 50 m/s.
By how much will each point on the negative be blurred?

9.   Why is the slide put into the slide projector upside down?

10. A projector using a slide 5 cm x 5 cm produces an image 2 m x 2 m on a screen 15 m from the lens of the projector. How far from the lens must the slide be?

11. What features of a slide projector produce high illumination of the slide?

12.  A screen is placed 100 cm from an object and a convex lens is used to give a real image of the object on the screen.
If the image is three times as big as the object find:
(a) the distance of the lens from the object; (b) the focal length of the lens.

13. Give two advantages of a reflecting telescope over a refracting telescope when used for astronomy.

14. How is the magnification of a simple refracting telescope found?

15. Binoculars are often termed ‘8 x 50’ What do these terms mean?

16. Say whether the images produced by each of the following are real or virtual:
(a) a magnifying glass  (b) the objective lens of a compound microscope;
(c) the lens in the eye   (d) the eyepiece lens of a telescope.

17. Suggest possible reasons why there is a limit to the useful magnification that you can get with:
(a) a telescope;
(b) an optical microscope;
(c)  the enlargement of a photographic negative.

18  What is the connection between the ‘f’ number and the amount of light that falls on the film in a camera?

19. What is an achromatic lens and why would it be used?

20. Draw a scale diagram to show a convex lens acting as a simple magnifying glass. For the diagram that you draw find:
(a) the magnification (b) the focal length of the lens.