JSS 3: Light energy (III)

                 Refraction of light 

Refraction is the bending of a light ray as it crosses the boundary between two media of different densities thereby causing a change in its direction 

                  Laws of refraction 

1. The incident ray, the refracted ray, and the normal at the point of incidence all lie on the same plane 

2. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for a given pair of media. 

The second law is also known as Snell's law 

                         n= sin i/ sin r 

Where n= Refractive index 

            i= angle of incidence 

            r= angle of refraction 

Example: The angle of incidence is 60° and the angle of refraction is 45°. Calculate the refractive index 

Solution:  n= sin i/ sin r 

                  n sin 60° /sin 45° 

                  n= 0.866/0.7071 

                  n= 1.22

n = speed of light in air/ speed of light in a substance 

Example: The speed of light in air is 3 x 10⁸m/s and the speed in glass is 2 x 10⁸ m/s. Calculate the refractive index of the glass.

Solution: 

n = speed of light in air/ speed of light in a substance 

n = 3 x 10⁸ / 2 x 10⁸

n= 1.5 

               The real and apparent depth 

1. Real depth: Real depth is the actual depth of an object in a medium 

2. Apparent depth: Apparent depth is the virtual depth that is observed as a result of the refraction of light.

n = Real depth / Apparent depth 

Example: What is the real depth of a swimming pool that appears to be 10m deep when viewed directly from above its surface? ( Refractive index of water = 4/3)

Solution:

n = Real depth / Apparent depth 

4/3 = Real depth/10 

Real depth= (4 x 10)/3

                   = 13.13m 

              Dispersion of white light 

Dispersion is the separation of white light into its component colors. The different component colors of white light are Red, Orange, Yellow, Green, Blue, Indigo, and Violet. (ROYGBIV)

Dispersion occurs because different colors of white light travel at different speeds through the glass. Rainbow is a natural dispersion of light drops of water and dust in the atmosphere.

                   Colors of light 

The primary colors of light are:

1. Red 

2. Blue 

3. Green 

The mixing of primary colors to produce other colors is called Additive color mixing or additive combination of colors.

All the primary colors combine to give white: Red + Blue + Green = White 

              

           The secondary colors of light 

The secondary colors of light are produced by mixing any two of the primary colors. The secondary colors of light are:

1. Yellow 

2. Cyan (Blue-green)

3. Purple (Magenta)

          Red + Green = Yellow 

          Red + Blue = Magenta (Purple)

          Blue + Green = Cyan

 

           Complementary colors of light 

Complimentary colors are colors that produce white light when mixed.

   Red + Cyan = White 

   Blue + Yellow = White 

   Green + Magenta = White 

                     Colors of paints 

The primary colors of the paint are:

1. Red 

2. Blue 

3. Yellow 

The addition of the primary colors of paints to produce other colors is called Subtractive color mixing.

The secondary colors of paints are:

1. Orange 

2. Green 

3. Purple 

   Red + Blue = Purple 

   Red + Yellow = Orange 

   Blue + Yellow = Green 

        Complimentary colors of paint 

The complimentary colors of paint produce Black color when mixed.

          Red + Green = Black 

          Yellow + Purple = Black 

           Blue + Orange = Black