CG Board Class 8 Science Refraction of Light Textbook Exercises which includes Fill in the blanks ,Question Answers and Extra Question and Answers from the Chapter.
Choose the correct alternative :-
(1) The refractive index of glass is…….
(a) 1.5 (b) 1.3 (c) 2.4 (d) 1.0
(2) The point from which a light ray passes without any deviation is
(b) Optical centre
(c) Focal length
(d) Centre of curvature.
(3) When light passes from one medium to another, it deviates from
its path. This is called :-
(a) Reflection of light
(b) Irregular reflection of light
(c) Refraction of light
(d) None of these
(4) When the object is placed at 2F. The image formed by a convex
lens will be at :-
(c) Between F and 2F
(d) Between F and optical centre.
Object placed at F -> On the side of the object
Object placed between F and 2F -> Beyond 2F
Object placed beyond 2F -> Between F and 2F
Object placed between F and Optical centre -> Beyond 2F
Q: What is a lens ? How many types of lens are there?
A lens is an optical device made of transparent material, often glass or plastic, with curved surfaces that can bend or refract light. There are two main types of lenses:
Convex Lens: This lens is thicker in the center and converges parallel light rays to a focal point. It is also called a converging lens.
Concave Lens: This lens is thinner in the center and diverges parallel light rays. It is known as a diverging lens.
Q: Define – (a) Principal axis (b) Optical centre (c) Focus
a. Principal Axis: The line joining the center of curvature of both the surfaces of the lens is called the principal axis.
b. Optical Centre: This is the center of the lens from which light rays pass without bending.
In a convex lens, the point at which light rays parallel to the principal axis converge is called the principal focus.
In a concave lens, the point from which these light rays appear to diverge is also called the principal focus.
Q: The picture formed on the screen at the theatre hall is real or virtual?
The picture formed on the screen in a theatre hall is a real image. This is because the light from the actors or objects on the stage converges to a point on the screen, and it can be captured on a physical screen or projection surface. Real images can be projected onto a screen and can be seen by the audience.