Class 8 General Science Notes: - Unit-9: Reflection and Refraction of Light: Solved Exercise (Long Questions and Answers)

(National Book Foundation - New Book/New Syllabus Based on National Curriculum Pakistan 2023-2024 and Onwards)

(Class 8 General Science Notes for 8th Centralized Exam 2023-2024 and onward, FDE, Islamabad)

C. Long Questions

Q1. State laws of reflection. Discuss how a plane mirror forms a virtual image.

Laws of Reflection:

The law of reflection describes the behavior of the incident and reflected rays.

1st Law: The incident ray, the reflected ray, and the normal to the surface all lie in the same plane.

2nd Law: The angle of reflection is equal to the angle of incidence.

Image formation by a Plane mirror:

When we look into a plane (flat) mirror, we see an image of ourselves two light rays leave from the top of an object. These rays reflect from the mirror and enter the eye. To the eye, it appears that the rays originate from behind the mirror. In a similar manner, two rays leave from the bottom of the object, therefore, at each point on an object, there is a single
corresponding point on the image. This image is formed by obeying laws of reflection and as it is appeared to originate from behind the mirror, represented by dashed lines it will be virtual by nature.

Q2. What is white light? How are the colours of light related to the reflection and absorption of light?

Ans:

White light:

White light is the ordinary visible light to our eyes. For example, the sun and the other stars are the sources of white light.

Colour of an Object:

The colours of the object or material are determined by the colors in the light it absorbs and those it reflects.

A material that reflects all colours of light appears white.
A material that reflects all colours of light appears black.
An object can reflect only those light colours that fall on it. for example, if blue light falls on a white piece of paper, the paper will appear blue, not white, because only blue light was available for it to reflect.
A mango absorbs most colours of light but reflects yellow, therefore mango looks yellow.

Q3. Explain the image formation by convex and concave mirrors?

Ans:

Image Formation in Concave Mirror:

Concave mirror form both real and virtual images.

When the concave mirror is placed very close to the object, a virtual and magnified image is formed.
If we increase the distance between the object and the mirror, the size of the image reduces and real images are formed.

Image Formation in Convex Mirror:

i. Convex mirrors always form virtual images. This is because the focal point and the Centre of curvature of the convex mirrors are imaginary points. So the image formed inside the mirror and cannot be taken on a screen.

ii. For the case of a convex mirror, the reflected rays will always be diverging, therefore, extended back behind the mirror with dashed lines to meet each other. The point at which the rays meet is the position at top of the image. Similarly, obtain the bottom part of the image

Unit-9: Reflection and Refraction of Light: Solved Short Questions and Answers

Class 8 General Science Notes

Source: General Science Book (National Book Foundation, Pakistan)

************************************

Shortcut Links For:

1.  5th Class All Subjects Notes
2.  8th Class All Subjects Notes

1. Website for School and College Level Physics
(https://askrarequiz.blogspot.com)
2. Website for School and College Level Mathematics
(https://askraremaths.blogspot.com)
3. Website for Single National Curriculum Pakistan - All Subjects Notes
(https://askrareclassnotes.blogspot.com/)

© 2023 & onwards Academic Skills and Knowledge (ASK)

Note:  Write me in the comments box below for any query and also Share this information with your class-fellows and friends.