Light coming from your computer screen, sun light, moon light, the filament bulb emitting light, candle light, street lights, the stars and galaxies releasing light! Oh my! Light and light everywhere!

If you have a glimpse at our guide to the properties of waves, you may discover that light is a type of a mechanical wave called as a transverse wave.

(Transverse waves are mechanical waves in which the vibrations are at right angles to the direction in which the wave is travelling.)

Sources of light

Light has got two remarkable sources:

  1. Luminous
  2. Non- luminous

Luminous light sources are those which produce their own light.

Non-luminous resources of light are those which don’t make their own light and instead reflect the light produced by luminous sources of light.

Here are some examples of luminous and non-luminous light:

Examples of luminous light resources:

  • The sun
  • A filament bulb
  • Fire
  • Candles
  • Electric lamps
  • Light emitting diodes (LED)
  • (And a million more that we’d like to tell in person!)

Examples of non-luminous light resources:

  • The moon
  • Pages of your physics textbook
  • Rocks
  • Minerals
  • Mountains
  • Your clothes
  • A car
  • (And yet a billion more that we expect you to discover!)

The reason why luminous objects emit light is due to their atoms which get energised when some energy flows through them or when they collide with each other.

Take the example of our sun; the sun is made up of hydrogen and helium gasses. Every second, energy is produced when two hydrogen atoms collide sadistically, giving out tons of light!

Shadows and light

When a ray of light hits an opaque object, it produces a shadow. Shadows are produced due to the fact that light travels in straight lines. The sharpness of a shadow depends upon the size of the source of light; the smaller the size of the source of light, the sharper the shadow produced.

The size of the shadow depends upon the distance of the object from the light source:

  1. The longer the distance of the object from the light source, the smaller the shadow produced.
  2. The shorter the distance of the object from the light source, the larger the shadow produced.

Who is faster, light or sound?

Ever observed a flash of lightening? (I bet you have!). Always, you first see the flash of lightening and then hear its crashing sound. This natural phenomenon clearly explains that the speed of light is faster than the speed of sound.

To be precise,

The speed of sound is 330 m/s in air at 00.

Whereas the speed of light is 300,000,000 m/s in air at 00.

Hence, the speed of light is 1 million times greater than the speed of sound!

Virtual and real images

A virtual image is an image that cannot be formed on a screen. A virtual image is formed when rays of light appear to be spreading out from a point.

When an object is reflected on a plane mirror, its image is virtual.

A real image is an image that can be formed on a screen.

For experiments which use lenses, a real image is formed on the screen.

Lateral inversion

When you stand in front of a mirror, your left shoulder appears to be at your right and vice-versa. This effect is only noticed in reflections involving plane mirrors. This phenomenon is known as lateral inversion (and thus your shoulder is said to be laterally inverted)


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