1.10 Reflection and refraction of light

Natural sciences

Grade 8

Energy: electricity, heat and light

Module 11

Reflection and refraction of light

• LIGHT is another common type of energy.
• You parents or educators would like to have "eyes at the back of their heads" or would like you to believe that they see everything. We know that this is impossible, though, and for a simple reason.

Activity:

To determine the terms and concepts that relate to light

[lo 2.1, lo 2.3, lo 2.4]

Light travels along a straight line.

Light can change direction, though, and this happens in two ways:

• Refraction
• Reflection

REFLECTION: We are going to look at reflection as it occurs with mirrors.

When a beam of light arrives at a certain angle, it will be reflected at the same angle.

ANGLE OF INCIDENCE = ANGLE OF REFLECTION

Activity:

To establish concepts relating to reflection [lo 2.4]

Assignment 1:

1. Draw a sketch of a mirror, showing the angle of incidence and the angle of reflection. Use a protractor.

Assessment of the Sketch

Has the sketch been drawn correctly?

[LO 2.4]

Curved mirrors

Curved mirrors have many applications. They enlarge or diminish and distort the image. A curved mirror can be CONCAVE. This will CONVERGE light beams towards a fixed point, the FOCUS.

Other mirrors may be CONVEX . They will cause light beams to DIVERGE (spread apart). This scales down the image. An application of this is evident in the rear view mirror of a motor car or in wing mirrors.

The same effect can be achieved with polished metals.

Assignment 2:

1. Try the following:

Polish the surface of a large serving spoon to get it to shine.

Look at your own image in the concave and on the convex side of the spoon and compare the shape of the reflections.

Draw the differences in the spaces that are provided:

Concave

Convex

Draw convergent and divergent beams from the right to add to the following sketches. Get your educator to help you.

Assessment of Sketches

Were you able to complete the sketches 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

Assignment 1:

LIGHT

• LIGHT is another common type of energy.

• You parents or teachers would like to have "eyes at the back of their heads" or would like you to believe that they see everything. We know that this is impossible, though, and for a simple reason

• Light travels along a straight line. Light can change direction, though. This can be achieved in two ways:

REFLECTION:

• We see this happening in the case of mirrors.

When a beam of light arrives at a certain angle, it will be reflected at the same angle.

Angle of incidence = angle of reflection

CURVED MIRRORS

• Curved mirrors have many applications.
• They enlarge and distort images.
• A mirror could be C ONCAVE

• It will CONVERGE light beams towards a fixed point, the FOCUS.
• Other mirrors may be CONVEX .
• They will cause light beams to DIVERGE (spread apart)
• This scales down the image.
• An application of this is evident in the rear view mirror of a motor car or in winged mirrors.

• Try the following:

• Polish the surface of a large serving spoon to get it to shine.
• Look at your own image in the concave and in the convex side of the spoon and compare the effect of the shape on the reflections.

Draw the differences in the spaces that are provided: