LIGHT
Class - 10, Chapter - 10, Subject - Science
Q.1 Define Refraction of Light.
Ans. The bending of light when it goes from one medium to another obliquely is called refraction of light.
Q.2 Why does Refraction take place?
Ans. The speed of light is different in different substances. The refraction of light is due to the change in the speed of light on going from one medium to another. Thus, when light goes from one medium to another, its speed changes. And this change in speed of light causes the refraction of light.
Q.3 Define Medium? What is its type?
Ans. Medium: A transparent substance in which light travels is known as a medium. Medium can be divided into two types:
(i) Optically Rarer Medium: A medium in which the speed of light is more is known as optically rarer medium (or less dense medium).
(ii) Optically Denser Medium: A medium in which the speed of light is less is known as optically rarer medium (or more dense medium).
Q.4 Explain Laws of refraction?
Ans. Laws of Refraction: According to laws of refraction of light,
(i) The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane.
(ii) The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for the light of a given color and for the given pair of media. This law is also known as Snell’s law of refraction.
If i is the angle of incidence and r is the angle of refraction, then,
Sin i / Sin r is constant.
This constant value is called the refractive index of the second
medium with respect to the first.
Q.5 Define refractive index.
Ans. Refractive Index : The refractive index of a medium is defined as the ratio of speed of light in vacuum to the speed of light in the medium. It is represented by n.
Q.6 What are the conditions when no refraction takes place?
Ans. Refraction will not take place under the following two conditions:
(i) When light is incident normally on a boundary.
A ray of light traveling in medium 1 falls normally. Therefore angle of incidence,
I = zero degree
When the refractive indices of two media are equal.
When refractive index of medium 1 is equal to refractive index of medium 2 i.e.
n1 = n2
Q.7 What are the rules of refraction?
Ans. Rule of Refraction:
Rule 1: When a light ray travels from a rarer medium to a denser medium, the light ray bends towards the normal.
Rule 2: When a light ray travels from a denser medium to a rarer medium, the light ray bends away from the normal.
Q.8 Refraction Through Glass Slab.
Ans. On passing through a rectangular glass slab, a ray of light suffers two refraction,
(i) While going from air to glass.
(ii) While going from glass to air.
Light emerges from the rectangular slab in a direction parallel to that in which it entered the glass slab. However the final emergent ray is slightly shifted sideways from the direction of the original incident ray by a distance 'D' called lateral shift. "The perpendicular distance between the original path of incident ray and the emergent ray coming out of the glass slab is called lateral displacement of the emergent ray of light."
The angle which the emergent ray makes with the normal is called the angle of emergence.
Q.9 What are the factors on which lateral displacement depends?
Ans. Lateral displacement depends mainly on three factors:
(i) Angle of incidence
(ii) Thickness of glass slab
(iii) Refractive index of glass slab.
Lateral displacement directly proportional to above factors i.e
Higher the values of these factors, greater will be the lateral displacement.
