1.11 Refraction of white light

Natural sciences

Grade 8

Energy: electricity, heat and light

Module 12

The refraction of white light

Activity:

To investigate the refraction of white light [lo 2.1, lo 2.4]

Splitting up of white light:

• This phenomenon can be demonstrated in the classroom by directing a beam of light through a PRISM. A prism is a triangular bar of glass or perspex. When this is done, you will see that white light is a combination of all the colours of the rainbow – this range of colours is known as the SPECTRUM.
• Red, having the longest wavelength, will experience the least refraction. Blue light, on the opposite side of the SPECTRUM , having the shortest wavelength, will show the greatest degree of refraction.

Assignment 1:

Ask your educator to demonstrate refraction.

Complete the sketch that follows by using coloured pencils to indicate the spectrum.

Assessment of the Sketch of the Spectrum

Were you able to complete the sketch correctly?

[LO 2.1]

Spectacles relieve the problems of people who suffer from short-sightedness or long-sightedness.

Assignment 2:

Differentiate between:

Near-sightedness:

L ong-sightedness:

The lenses of spectacles can be like the reflective surfaces you learnt about earlier, convex or concave. These lenses are shaped on both sides and are therefore biconvex or biconcave.

This shape is __________________________________________

Draw these lenses, showing the refraction that results from each type of lens. You might need to ask your educator’s help.

Assessment of the Sketch of the Spectrum

Were you able to complete the sketch correctly?

[LO 2.4]

Assessment

LO 2: Constructing Science Knowledge:

The learner will know and be able to interpret and apply scientific, technological and environmental knowledge.

This is evident when the learner:

• recalls meaningful information;

• interprets information;

2.4 applies knowledge.

Memorandum

SPLITTING UP OF WHITE LIGHT:

Assignment 1:

• This phenomenon can be demonstrated in the classroom by directing a beam of light through a PRISM.

• A prism is a triangular bar of glass or perspex.

• When this is done, you will see that white light is a combination of all the colours of the rainbow – this range of colours is known as the SPECTRUM .

• The different colours that are combined to form white light do not move at the same speed.
• Red, having the longest wavelength, will experience the least amount of refraction. Blue light, on the opposite side of the SPECTRUM , having the shortest wavelength, will show the greatest degree of refraction.

Complete the sketch that follows by using coloured pencils to indicate the spectrum.

Spectrum colours:

Violet, blue, green, yellow, orange, red

• Spectacles relieve the problems of people who suffer from shortsightedness of farsightedness .

• NEAR-SIGHTEDNESS : People with this condition can see close objects well, but objects in the distance are unclear.
• LONG-SIGHTEDNESS : People with this condition can see distant objects clearly but find it difficult to focus on nearby objects and find reading difficult, for instance. Older people, in particular, develop this problem.

• The lenses of spectacles can be shaped, like the reflective surfaces about which you have learnt earlier, to be convex or concave. These lenses are shaped on both sides and are therefore biconvex or biconcave .

• Further possibilities:
• Lens refraction
• Pinhole camera and binoculars