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Light : What is Light? Light carries energy and travels as a wave. Light travels at 300 000 000 m/s or 300 000 km/s (much faster than sound). Light waves travel in straight lines. © Boardworks Ltd 2003 © Boardworks Ltd 2003 © Boardworks Ltd 2003 Light : What materials will light travel through? Hold different materials between the lamp and the screen. Use the results table and shading chart on the next slide to estimate the opacity of different materials. © Boardworks Ltd 2003 What materials let light through? Material Tracing paper Opacity [%] Shading chart. 100% 1 ply tissue 2 ply tissue 75 % Smoked glass 50 % Glass 30 % Perspex Wood 2.5 % 5% 10 % 15 % 25 % 20 % 0% Opaque objects do not allow light to pass through them - transparent ones do. Translucent materials only let through part of the light. © Boardworks Ltd 2003 How does light travel? 1) Fill a clear glass trough or empty fish tank with smoke. 2) Shine rays of light through the tank and describe what you see. LIGHT WAVES TRAVEL IN STRAIGHT LINES. © Boardworks Ltd 2003 Seeing objects How do we see an object? The light from the object enters our eye. Do we see all objects in the same way? There are two ways we see objects….. • We see some objects by reflected light. • We see other objects because they are light sources. © Boardworks Ltd 2003 Light sources How do light rays from a light bulb and other light sources reach our eye? They travel in a straight line directly into our eye. © Boardworks Ltd 2003 Reflected light How do light rays from a book and other such (non-luminous) objects reach our eye? Light from the lamp or another light source strikes the book and some of the light is reflected into our eye. © Boardworks Ltd 2003 What happens to the light which isn’t reflected? • Some of this light may be absorbed (e.g. as heat). • Some of this may also be transmitted (e.g glass reflects a small amount of light, absorbs some of the rest and allows most of it to pass through. © Boardworks Ltd 2003