Free download NCERT Solutions for Class 10 Science Chapter 10 Light – Reflection and Refraction in PDF form. NCERT solutions for class 10 Science other chapters are also in PDF as well as online to use.
NCERT Solutions for Class 10 Science Chapter 10
Important Questions from Light – Reflection and Refraction
Class 10 Science – Physics
Give three points of difference between real and virtual images.
(i) Here the rays actually meet at the image point.
(ii) It can be taken on a screen.
(iii) It is always inverted
(i) Here the rays appear to diverge from the image point.
(ii) It cannot be taken on a screen.
(iii) It is always erect.
List four properties of the image formed by a plane mirror.
Properties of images formed by a plane mirrors:
(i) The image formed by a plane mirror is virtual and erect.
(ii) It is of the same size as the object.
(iii) The image is formed as far behind the mirror as the object is in front of it i.e., u = v.
(iv)It is laterally inverted i.e., image is inverted sideways with respect to the object.
Define the principal focus of a concave mirror. Calculate the focal length of the mirror of radius of curvature of 20 cm.
The principal focus of concave mirror is a point on its principal axis at which a beam of light parallel to the principal axis actually converges after reflection from the mirror.
Focal length = R/2 = 20/2 = 10 cm.
List the four properties of the image formed by a convex mirror.
Properties of the image formed by a convex mirror:
(i) This image is always virtual and erect.
(ii) The image is highly diminished or point sized.
(iii) It is always formed between F and P.
(iv) As the object is moved towards the pole of convex mirror, image also moves towards its pole and gradually increases size till its size becomes almost equal to that of the object.
State the type of mirror preferred as (i) rear view mirror in vehicles, (ii) shaving mirror. Justify your answer giving two reason in each case.
(i) A convex mirror is preferred as a rear-view mirror because
(a) It always forms an erect, virtual and diminished image of an object placed anywhere in front of it.
(b) It has wider field of view.
(ii) A concave mirror is preferred as a shaving mirror because when it is held closer to the face, it form:
(a) an enlarged image of the face
(b) an erect image of the face
What is meant by refraction of light?
Refraction of light: The phenomenon of bending of light from its straight line path as it passes obliquely from one transparent medium to another is called refraction of light.
The path of the ray of light in the first medium is called incident ray.
The path of the ray of light in the second medium is called refracted ray.
The angle between the incident ray and the normal at the surface of separation is called angle of incidence (i).
The angle between the refracted ray and the normal at the surface of separation is called angle of refraction (r).
State the laws of refraction of light.
Laws of refraction of light: The refraction of light obeys the following two laws:
First law: The incident ray, the refracted ray and normal to the surface of separation at the point of incidence, all lie in the same plane.
Second law: The ratio of the sine of the angle of incidence and the sine of the angle of refraction is constant for a given pair of media. Mathematically,
[sin i] / [sin r] = n (a constant).
The ratio n2 is called refractive index of the second medium with respect to the first medium. The second law of refraction is also called Snell’s law of refraction.
Briefly explain the cause of refraction of light.
Explain why a ray of light bends towards the normal as it passes from a rarer medium to a denser medium?
Cause of refraction of light: Light travels with different speeds in different media. The bending or refraction of light occurs due to the change in the speed of light as it passes from one medium to another medium. Using Snell’s law of refraction, we can write
n = [sin i] / [sin r] = c/v
As the speed of light (c) in vacuum is greater than the speed of light (v) in any medium or c > v, so sin r or angle i > angle r. That is why, a ray of light bends towards the normal as it passes from a rarer medium (air) to a denser medium (glass).
Distinguish between a concave and convex lens.
(a) It is thicker at the centre than at the edges.
(b) It converges a parallel beam of light on refraction through it.
(c) It has a real focus.
(a) It is thinner at the centre than at the edges.
(b) It diverges a parallel beam of light on refraction through it.
(c) It has a virtual focus.