The Nature of Light Answer Sheet (Introductory)

Transcription

1 The Nature of Light Answer Sheet (Introductory) Author: Sarah Roberts

2 - Faulkes Telescope Project What is light? 1. Arrange the following objects in the table below according to whether they are sources or reflectors of light: Source of light Reflects light The Sun Candle flame Torch Asteroids The Moon Planets Stars The Speed of Light When astronomers talk about the very large distances in space, they use units of light-years. This is the distance that light takes to travel at a speed of 3x10 8 m/s in one year. 1. The Andromeda galaxy is 2.9 million light years from Earth. a) How long does it take for light from Andromeda to reach Earth? 2.9 million years b) If we sent a message from Earth to the Andromeda galaxy, how long would it take for us to get a reply? 2.9 million light years x 2 = 5.8 million light years if the message was sent at the speed of light and the reply was instantaneous Page 2 of 9

3 - Faulkes Telescope Project 2. It takes about 7000 years for light from the Eagle nebula to reach us on Earth. a). How far is the Eagle nebula from Earth in light years? 7000 light years b). Given the formula, speed = distance time and that the speed of light is 3x10 8 m/s, how far (in km) will light travel in one year? 1year = seconds = distance m = distance km = distance c). From your answer to (b), calculate how far the Eagle nebula is from Earth in km. Eagle nebula = 7000 lightyears distance in km = km = km Page 3 of 9

4 - Faulkes Telescope Project The Path of Light Objects which block light and don t let any through are opaque. Those which allow some light through are translucent, whereas transparent objects allow all light through. 1. State whether the following objects are transparent, translucent or opaque. a). A brick wall Opaque b). Eyeglasses Transparent c). Windows Transparent d). Frosted glass (like on a bathroom window) Translucent e). Cardboard Opaque 2. a) Is your body opaque, translucent or transparent? Your body blocks light, and is therefore opaque. This causes our shadow. b). Thinking about your answer to part (a) above, what do you think would happen to the light in the diagram below as it hits Jack? The light would be blocked by Jack s body, thus causing a shadow on the ground. Page 4 of 9

5 - Faulkes Telescope Project Reflection B A 1. The light rays in the diagram above are labelled A and B. a). Which is the incident ray of light, A or B? Ray A is the incident ray of light. b). If the angle of reflection, r, is 15 degrees, at what angle did the incident ray hit the mirror? The incident ray hit the mirror at an angle of 15 degrees. 2. The following is a simple design of a periscope. Draw the path that light takes in the periscope if your eye is at A. Page 5 of 9

6 - Faulkes Telescope Project 3. Using the information above, and the flash animation (if you watched it), draw the path of the light rays as they journey through the telescope below. Make sure you mark the directions of the rays. Page 6 of 9

7 - Faulkes Telescope Project Refraction 1. The human body contains a lens. a). Where can this lens be found? In the eye b). Is this lens, convex or concave? The eye contains a convex lens - it focusses light onto the focal point, which is on the retina. 2. Draw the path that light takes as it is refracted by a convex lens. On this diagram, mark the direction of the rays, and label the focus point, and the focal length of the lens. focal length Page 7 of 9

8 - Faulkes Telescope Project 3. Select the true statements from the following by ticking the boxes: a). When light bounces off a mirror, it is said to have been refracted b). When light bounces off a mirror, it is said to have been reflected c). The angle at which light comes off a mirror is equal to the angle at which it hits the mirror d). The angle at which light comes off a mirror is larger than the angle at which it hits the mirror e). The angle at which light comes off a mirror is smaller than the angle at which it hits the mirror 4. a). Using the following words, fill in the blanks in the paragraph below: Refracted Reflected Reflection Incidence Greater than Telescope Lenses Less than Equal to When light hits a mirror, it is reflected. The angle at which it hits the mirror is called the angle of incidence. The angle at which the light ray comes off the mirror is called the angle of reflection. This angle is equal to the angle of incidence. Light can also be made to change direction with the use of lenses. Page 8 of 9

9 - Faulkes Telescope Project b). Now find and circle the words which you used above, in the word-search below. R E F R A C T E D A E B A E G R S V L Q F E K F Q E O D S P L T Y L C U P H E Q E F O E T D A F R U C M S C J O I L N S T K R T A F N D T E I N L E N S E S A O O W R D U G W V G H N E C N E D I C N I Page 9 of 9