#2 #6 #8#162. A 5-cm diameter ball is located 50 cm in front of a pinhole camera. If the film is located 10 cm from the pinhole, what is the size of the image on the film?
This problem is solved by carefully drawing a ray diagram to scale, as shown. Remember that a light ray travels in a straight line unless it encounters something different!
6. What is the radius of the spherical surface that would produce a mirror with a focal length of 3 m?
The focal point of a spherical mirror is on the optic axis at the midpoint between the center of the sphere and the center of the mirror (one radius away from the center). The radius of the sphere is then twice the focal length, or 6 meters.
8. An object is located three times the focal length from a concave spherical mirror. Draw a ray diagram to locate its image. Is the image real or virtual, erect or inverted, magnified or reduced in size?
Draw a careful ray diagram of this problem, using the three special light rays:
The image is real, inverted, and reduced.
16. The average distance from the surface of the earth to the surface of the moon is 376,000 km. How long after a large flash occurs on the moon's surface would it take for observers on earth to see it?
Recalling that light travels in vacuum at a constant speed of about
c = 300,000,000 m/s, we use the distance equation d = c t to get