HALF QUESTION Typical of Question 12 in Leaving Cert. Exam
Q7 Answer both of the following parts (a) and (b). (a) Fig 13.36 shows a ray of light travelling from water to air. At B the ray of light undergoes refraction.
What special name is given to the angle of incidence i, when the effect shown in the diagram occurs? (6)
In the diagram the value of the angle i is 48.6. Calculate a value for the refractive index of the water. (6)
Fig 13.36
Draw a diagram to show what happens to the ray of light when the angle of incidence i is increased to 50.
A swimmer, at a depth of 10 m, observes a disc of light on the surface of the water. (i) What is this region of light called? (ii) What is the radius of this disc? (b) State the laws of refraction of light.
A converging lens has a focal length of 30 cm. Find the two positions at which an object may be placed so that the image formed may be twice the size of the object.
CHAPTER CHECKLIST FORMULAE:
n sin i sin r
n =
c1 c2
1 f 1
P 1 f
u 1 v
m v u
apparent depth 1 real depth sin C Refractive index Refractive index in terms of relative speeds Focal length of lenses Magnification Power of a lens Air B i Water
(6)
(10) (6)
A converging lens is used as a magnifying glass. Draw a ray diagram to show how an erect image is formed by a magnifying glass.
