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Y210 · Light and Waves
KO

Middle school year 2 · third unit

Light and Waves

You in the mirror, big letters under a magnifying glass, the countless colours of a screen, a song from a speaker: all come from light and sound bouncing, bending, overlapping and vibrating by fixed rules. Move those rules by hand.

One student forming an image of a candle with a lens and another shining a light at a mirror

Where does light go when it hits a mirror?

A board to adjust

It does not bounce just anywhere. Take the laser, move it, and hit the target with the reflected light.

Hold a magnifying glass far away and the world turns upside down

A board to adjust

Close up it enlarges; far off it inverts. Why? Take the candle and drag it toward the lens, then away.

A screen has only red, green and blue lights

A board to arrange

So how do we see yellow, or white? Drag the three lights over one another.

What is the difference between a loud sound and a high one?

A board to adjust

Drawn as a picture, sound is a wave. Drag the handles to change the height and the length of the wave.

What to take away from this unit

  1. Light leaves a mirror at the same angle it arrived: angle of incidence = angle of reflection, the law of reflection. The image in a flat mirror is the same size as the object and appears reversed left to right.
  2. Light bends as it enters a different material (refraction). A convex lens gathers light; a concave lens spreads it. A convex lens gives an upside-down image of an object beyond its focus, and an upright, larger one of an object inside it.
  3. Red, green and blue are the primary colours of light. Overlapped they make other colours, and all three make white. The colour of an object is the colour of the light it reflects.
  4. A wave is a vibration spreading outward. The size of the vibration is the amplitude, the distance travelled in one vibration is the wavelength, and the number of vibrations a second is the frequency. Waves that vibrate up and down as they travel, like ripples, are transverse; those that vibrate back and forth, like sound, are longitudinal.
  5. A sound is louder with a bigger amplitude and higher with a higher frequency. Instruments sound different because their wave shapes differ: this is timbre.