Refraction Sample Problems
1. A light ray is incident on crown glass (n=1.52) at an angle of 30° to the normal. It is incident from
air. What is the angle of refraction?
2. A ray of light falls on a lake surfaces at an angle of 35° to the surface of the water (n=1.33). Draw
the incident and the reflected rays. Determine the magnitude of the reflected ray. Draw the refracted
ray. Determine the magnitude of the refracted ray.
3. A light ray passes from air into an unknown substance. The incident angle is 23° and the refracted
angle is 14°. What is the index of refraction of the unknown substance?
4. The index of refraction of water is 1.33. What is the speed of light in water?
5. The speed of light in a substance is 2.56 x 108m/s. What is the index of refraction of the substance?
6. What is the critical angle for a diamond (n=2.42) to air boundary?
7. What is the critical angle for a gemstone whose index of refraction is 1.86?
Lenses Sample Problems
Describe the image mathematically and using a ray diagram. Find the magnification ratio. Always use a 1
cm high object.
1.
2.
3.
4.
5.
An object is placed 30 cm in front of a convex lens with a 10 cm focal length.
An object is placed 10 cm in front of a convex lens with a 6 cm focal length.
An object is placed 5 cm in front of a convex lens with a 10 cm focal lenght.
An object is placed 15 cm in front of a concave lens with an 8 cm focal length.
An object is placed 3 cm in front of a concave lens with a 5 cm focal length.
Refraction Homework
1. A ray of light traveling through air is incident upon a sheet of crown glass (n=1.52) at an angle of
30° to the normal. What is the angle of refraction? Ans: 19.2°
2. A ray of light passes into water from air at an angle of 50° to the lake's surface. What is the angle of
refraction? What is the speed of light in the water? Ans: 28.9°; 2.25 x 108m/s
3. Calculate the speed of light in a diamond. Ans: 1.24 x 108m/s.
4. A block of unkown material is submerged in water. Light in the water is incident on the surface at an
angle of 31°. The angle of refraction is 27°. What is the speed of light in the unknown material? Ans:
1.20 x 108m/s
5. What is the critical angle for light rays passing from diamond (n=2.42) into air? Ans: 24.42°
6. What is the critical angle for light rays passing from quartz (n=1.54) into water (n=1.33)? Ans:
59.73°
7. The critical angle for light rays passing from water into air is 48.75°. What is the index of refraction
of water? Ans: 1.33
Lenses Homework
1. Use a ray diagram to locate the image formed: A 1 cm high object is located 6 cm in front of a
concave lens having a 10 cm focal length.
2. Use a ray diagram to locate the image formed: A 4 cm high object is located 10 cm in front of a
concave lens having a 16 cm focal length.
3. Use a ray diagram to locate the image formed: A 3 cm object is located 9 cm in front of a convex
lens having a 6 cm focal length.
4. Use a ray diagram to locate the image formed: A 2 cm object is located 4 cm in front of a convex
lens having an 8 cm focal length.
5. Use a ray diagram to locate the image formed: A 0.6 cm object is located 1 cm in front of a
magnifying glass having a 2 cm focal length.
Mathematically determine the image distance, the image height, and the magnification ratio. Describe the
image formed, relating image and object distance, image and object height, and type of image, and image
orientation.
1. A 6 cm object is located 30 cm in front of a convex lens having a focal length of 10 cm. Ans: 15 cm;
-3 cm; -0.5
2. A 2 cm object is located 4 cm in front of a convex lens having a focal length of 6 cm. Ans: -12 cm; 6
cm; 3
3. A 1 cm object is located 5 cm in front of a concave lens having a focal length of 4 cm. Ans: -2.22
cm; 0.44; 0.44
4. A 2 cm object is located 8 cm in front of a diverging lens having a focal length of 3 cm. Ans: -2.18
cm; 0.55 cm; 0.28
5. A camera lens having an 8 cm focal length is 10 cm from the film. The image will be formed on the
film. Where must an object be located in order for this picture to be in sharp focus? Ans: 40 cm
away