Plane trigonometry with practical applications, by Leonard E. Dickson.

Ch. III]

TRAVERSE TABLE

33

EXERCISES ON REFRACTION OF LIGHT
1. A pebble lies at the bottom of a pool of water 6 feet deep. How
far below the surface will the pebble appear to a man above if his line of
sight makes 8~ with the perpendicular to the water?
2. Find the displacement CF (Fig. 21) of a ray of light passing through
a crown glass plate 0.258 in. thick at the angle ABP = 55~50' with the
perpendicular to the plate.
3. A man whose eye is at a point A, 10 feet above the level of the
water BH (Fig. 21), sees at B the image of the foot C of a pile HC
driven in the water. His horizontal distance from B is 24 feet, and from
the pile 78 feet. Find the length HC of the pile below water.
4. If a ray of light passes through water and makes angle i with the
perpendicular to the surface of the water, the largest value of i for which
the ray will emerge into the air is C, where sin C = 3/4; while, for i>C,
the ray is wholly reflected by the surface back into the water. Find this.
critical angle C. Will a ray having i = 50~ be refracted or all reflected?
5. If the critical angle (Ex. 4) for crown glass is 42.5~, what is the
index of refraction from crown glass to air? A crown glass prism, whose
cross section is an isosceles right triangle, acts as a total reflector for rays
entering at right angles to either perpendicular face.