Learning About Light (1955)

[Music] playing blindman's buff is lots of fun jane's caught and now it's her turn to be blindfolded when her eyes are covered everything goes black jane sees nothing but as soon as she removes the handkerchief she can see again do you know what happens when jane covers her eyes she shuts off the light that all the things and children in the room send to her eyes when jane peaks she sees her friends again she can see some objects like this bulb because they give off their own light we call such objects luminous or light giving but the ball on the table next to jane is not luminous it gives no light by itself jane can see the ball only because the lamp shines on it we say that the ball reflects the light from the lamp turn off the lamp and we can't see the ball we see some objects because they reflect light remember the word reflect it means bounce off others like the lamp are luminous the sun is luminous it gives off the light which makes it possible for us to see things in the daytime the man sees the tree mainly because sunlight is reflected from it to his eyes but not only daylight comes from the sun moonlight comes from the sun too sunlight falls on the moon and some of it is reflected to the earth light travels very fast jane can see the light go off as soon as piggy turns off the switch and light travels in straight lines that's why piggy cannot see jane when she goes around the corner because light travels in straight lines we cannot see very far on our earth watch the ship disappear as it sails beyond the horizon the earth is round and light cannot curve with the earth nor can light pass through the earth but light can pass through some materials we see jane through the window because light can go through glass glass is transparent air is also transparent and so is clear shallow water transparent means that light passes through easily other materials like the lampshade and frosted glass let some light through they are translucent other materials again such as the ball this end table or the globe let no light pass through such materials are called opaque when jane covers peggy's eyes everything goes dark because the handkerchief is also opaque because jane's hand is opaque it stops the light from passing through it therefore it leaves a dark mark behind it on the wall which we call a shadow translucent objects throw lighter shadows but transparent glass casts hardly any shadow can you tell why watch piggy and jane in front of the mirror do you notice that jane can see peggy in the mirror but not herself piggy can see jane but not herself let's find out why light which strikes a mirror acts very much like a ball thrown at a smooth floor when you throw a ball straight down it will bounce straight up into your hand but when you throw the ball at a slant it'll bounce away in the opposite direction observe the angle at which the ball strikes the floor it is called the angle of incidence and it is the same size as the angle at which the ball bounces away called the angle of reflection in this drawing several beams of light are pictured falling on the mirror at an angle they bounce back at an angle of the same size but in the opposite direction in science we say that the angle of incidence is always equal to the angle of reflection once again the angle of incidence equals the angle of reflection can you now understand why piggy can see jane in the mirror but not herself but look what happens when a mirror isn't flat how long one face looks and how squashed the other try to find out why the mirror helped us get acquainted with reflection now let's try another kind of experiment did you ever notice how a pencil seems broken or bent when seen through water that's because light rays seem to bend when they pass from water through the air to our eyes a straw also looks bent in each instance the two materials water and air differ in a characteristic called density water is denser than air this drawing shows what happens when light passes from one transparent material into another of different density it bends we call this bending refraction light is also refracted are bent when passing through glass and that is very important many children and grown-ups depend upon refraction for the help their glasses give them glasses or lenses which bend the light that all objects send to the eyes those who cannot see well are helped by lenses specially made to correct poor eyesight thanks to refraction we can use lenses for many useful instruments such as magnifying lenses and microscopes which makes small things look big and telescopes which make far away things seem close and photographic equipment like the camera which made this motion picture in this film you have learned several things about light how it travels why some objects are transparent why others are called translucent and others opaque you have seen how light is reflected and refracted and why these principles are so important can you use these new words and rules about light to explain how these girls see their images in this mirror and why you were able to see this motion picture on the screen [Music] you