Last updated on February 9th, 2024 at 04:28 pm
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
the-
(a) Focus
(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 :-
(a) 2F
(b) F
(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.
c. Focus:
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.
Q: What is the minimum distance at which a clear image can be visualized?
The minimum distance at which a clear image can be visualized is typically around 25 centimeters (or 10 inches).
Q: Where is the image formed in a human eye?
The image is formed in the retina of the human eye.
Q: What is shortsightedness ? How can it be rectified?
Shortsightedness, also known as myopia, is a vision condition in which a person can see objects up close clearly, but distant objects appear blurred. Myopia can be rectified by using concave (diverging) lenses.
Q: What do you understand by longsightedness ? How can this be rectified?
Longsightedness, also known as hypermetropia or hyperopia, is a vision condition in which a person has difficulty seeing nearby objects clearly, but distant objects are seen more clearly. Hypermetropia can be rectified by using convex (converging) lenses.
Q: What do you understand by refraction?
Refraction is the bending of light as it passes from one transparent medium into another, causing a change in its direction due to differences in the speed of light in each medium.
Q: When the light ray enters water medium through glass medium, where will it deflect – towards normal or away from the normal?
When a light ray enters water through glass , it will deflect towards the normal because it goes from a rarer medium to a denser one.
Q: What do you understand by refractive index of a medium?
The refractive index of a medium is a measure of how much the speed of light is reduced when it passes through that medium compared to its speed in a vacuum.
