Physics Chapter 5 - Light (Teacher's Guide)

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CHAPTER 5: LIGHT

In each of the following sentences, fill in the bracket the appropriate word or words given below.

solid, liquid, gas, vacuum, electromagnetic wave, energy

1. Light is a form of ( ).
2. It travels in the form of ( ) 3. In can travel through ( ) 4. It travels fastest in the medium of ( ) 5. Light of different colours travels at the same speed in the medium of ( )

Light allows us to see objects.
Light can be reflected or refracted.

1. UNDERSTANDING REFLECTION OF LIGHT

Plane mirror and reflection: In the boxes provided for the diagram below, write the name of each of the parts indicated. [pic]
Laws of Reflection: State the laws of reflection.

i) …………………………………………………………………………………………….

………………………………………………………………………………………..……. [pic]
ii) ……………………………………………………………………………………………..

…………………………………………………………………………………………….. Exercise 1: The diagram below shows how the relationship between incident angle and reflected angle can be investigated. Fill in the values of the angles of reflection, r in the table below

[pic]
Exercise 2:
[pic]
Image formed by a plane mirror: Using the law of reflection, complete the ray diagram to determine the position of the image. [pic]
What can you say about the line joining object and image? ………………………………………

What can you say about the distances AB and BC? ………………………………………………..

Differences between real and virtual image:
[pic]

Characteristics of image formed by plane mirror: Observe the pictures below as well as using previous knowledge, list the characteristics.

[pic]

Exercise 1:
[pic]

Exercise 2:

[pic]

Exercise 3:
[pic]

ACTIVITY: Find out some of the uses of plane mirrors (application of reflection).

Curved Mirrors:
[pic]
Terminology: Refer to the diagrams above and give the names for the following: [pic]

Effect of curved mirrors on incident rays:

a) Incident rays parallel to the principal axis:
[pic]

Study the diagrams above and fill in the blanks for the following sentences. [pic]
r = 2f

b) Incident rays parallel to each other but not parallel to the principal axis:

[pic]

Study the diagrams above and fill in the blanks in the following sentences.

▪ Parallel rays converge at a point called ……………………………

▪ The ray passing through C is reflected back along the line of the…………………….ray.

▪ The distance between the focal plane and the mirror is the ………………………….,f.

Image formed by curved mirror (ray diagram method)

Principle of drawing ray diagrams:

a. Rays parallel to the principal axis are reflected through the principal focus, F.

[pic]

Exercise 1: Complete the ray diagrams below:
[pic]

b) Rays passing through the principal focus are reflected parallel to the principal axis.

[pic]

Exercise 2:
a) Complete the ray diagrams below:
[pic]

b) Rays passing through the center of curvature are reflected directly back. [pic]

Exercise 3: Complete the ray diagrams below:
[pic]

Image formed by concave mirror:

Using the principles of construction of ray diagram, complete the ray diagrams for each of the cases shown below:

u = object distance; v = image distance; f = focal length; r = radius of curvature

Case 1: u > 2f

[pic]

Hence state the characteristics of image formed:

i) ii) iii)

Case 2: u = 2f or u = r
[pic]
Characteristics of image formed:

i) ii) iii)

Case 3: f < u < 2f
[pic]
Characteristics of image formed:...
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