LIGHT BOX EXPERIMENT OBJECTIVES: Distinguishing between electromagnetic and mechanical waves. Comparing diffraction, reflection and refraction. VOCABULARY: Diffraction reflection refraction wave lens concave lens convex lens MATERIALS: BACKGROUND: Waves are DISTURBANCES by which energy travels. Many different particles move in waves. The waves on an ocean are mechanical waves caused mainly by wind. Light is an electromagnetic wave caused by excited electrons. Light acts as a wave and as a particle. Both electromagnetic and mechanical waves reflect, refract and diffract energy. These properties of wave motion are important because they explain how waves move. The phone, television, radio, microwaves, CD players, lasers, video players and many other items are products produced by electromagnetic waves. Diffraction is when a wave goes through a small hole and has a flared out geometric shadow of the slit. Diffraction is a characteristic of waves of all types. We can hear around a corner because of the diffraction of sound waves. For instance, if a wall is next to you when you yell, the sound will parallel the wall. The wall may stop the sound, but the voice doesn't; sound will almost turn the corner of the wall. This is diffraction. Reflection is when waves, whether mechanical or electromagnetic, bounce from a surface back toward the source. A mirror reflects the image of the observer. Refraction is when waves, whether mechanical or electromagnetic, are deflected when the waves go through a substance called medium. The wave generally changes the angle of its general direction. Reflection When reflection occurs, it can be seen that the angle of incidence is equal to the angle of reflection for a conducting surface as would be expected for light. When a signal is reflected there is normally some loss of the signal, either through absorption, or as a result of some of the signal passing into the medium. Refraction It is also possible for radio waves to be refracted. The concept of light waves being refracted is very familiar, especially as it can be easily demonstrated by placing a part of pencil in water and leaving the remaining section in air. It is possible to see the apparent change or bend as the pencil enters the water. Mirages also demonstrate refraction and a very similar effect can be noticed on hot days when a shimmering effect can be seen when looking along a straight road Diffraction Radio signals may also undergo diffraction. It is found that when signals encounter an obstacle they tend to travel around them. This can mean that a signal may be received from a transmitter even though it may be "shaded" by a large object between them. Dispersion of Light The fact that refractive indices differ for each wavelength of light produces an effect called dispersion. This can be seen by shining a beam of white light into a triangular prism made of glass. White light entering such a prism will be refracted in the prism by different angles depending on the wavelength of the light. 1. Draw a diagram where you explain the observations made with the box of light. 2. Insert the following names: angle of incidence, angle of reflection, normal. 3. Identify refraction and reflection. 4. Draw a concave mirror and a convex mirror in an object.