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Phys 122/Phys 120: Geometric Optics Question Paper
Phys 122/Phys 120: Geometric Optics
Course:Bachelor Of Education (Science) & Bachelor Of Science
Institution: Chuka University question papers
Exam Year:2013
CHUKA
UNIVERSITY
UNIVERSITY EXAMINATIONS
FIRST YEAR EXAMINATION FOR THE AWARD OF DEGREE OF
BACHELOR OF EDUCATION (SCIENCE) &
BACHELOR OF SCIENCE
PHYS 122/PHYS 120: GEOMETRIC OPTICS
STREAMS: B.Ed (Sci), B.Sc Y1S2 TIME: 2 HOURS
DAY/DATE: THURSDAY8/8/2013 2.30 P.M. – 4.30 P.M.
INSTRUCTIONS:
Answer question ONE and any other TWO questions.
Question One
Use Fermat’s principle to derive the laws of reflection. [8 marks]
A contact lens is made of plastic (n = 1.58) f = 25cm and its inner surface has R = 18cm. What is the radius of curvature of the outer surface? [4 marks]
State two lens aberrations. Briefly explain how they occur and how they are corrected.
[6 marks]
Briefly describe how dispersion of light is demonstrated using a glass prism.
[4 marks]
Show that ?_c=?sin?^(-1) n_2/n_1 where ?_c is the critical angle. [4 marks]
Compare and contrast the spherical mirrors and thin lenses. [4 marks]
Question Two
Two light pulses are emitted simultaneously from a source. Both pulses travel to a detector but one first passes through 6.2m of ice (n = 1.309). Determine the difference
inthe pulses’ times of arrival at the detector. [6 marks]
A layer of ice (n = 1.309), having parallel sides, floats on water (n = 1.33). If light is incident on the upper surface of the ice at an angle of incidence of 30o, what is the angle of refraction in the water? [6 marks]
A narrow bean of light is incident from air onto a glass surface (n = 1.56). Find the angle of incidence for which the corresponding angle of refraction is ½ the angle of incidence (Sin 2?=2 Sin? cos?). (8 marks]
Question Three
A ray of light strikes the midpoint of one face of an equiangular glass prism (n = 1.5) at an angle of incidence of 30o.
Trace the path of light ray through the glass and find the angles of incidence and refraction on each surface.
Find the angle of deviation between the incident ray and the emergent ray.
[10 marks]
A cylindrical cistern, constructed below ground level is 3m in diameter and 2m deep and is filled to the brim with a liquid of n = 1.5. A small object rests at the bottom of the cistern at its centre. How far from the edge of the cistern can a girl whose eyes are 1.2m above the ground stand and still see the object? (Draw scale diagrams for both (a) and (b). [10 marks]
Question Four
Derive the lens equation. [8 marks]
A convex lens of focal length 10cm forms the image of an object, 3cm in height, placed 30 cm in front of it.
Find the location and characteristics of the image by geometrical construction.
Repeat (1) above by using the lens equation and compare your findings.
[12 marks]
Question Five
Find the object distance (in terms of f) for a thin converging lens of focal length f. If the image is virtual and the image is three times the focal length, find the magnification of the image. Draw a sketch of the arrangement. [8 marks]
Object O, is 15cm to the left of a converging lens of 10cm focal length. A second lens is positioned 10cm to the right of the first lens and is observed to form a final image at the position of the original object.
What is the focal length of the second lens?
(ii) What is the overall magnification of the system?
(iii) What is the nature of the final image? [12 marks]
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