Very short answer-Class 10 -Science- Physics-Chapter 10 – Light – Reflection and Refraction

Class 10 -Science-Very short answer- Physics-Chapter 10 – Light – Reflection and Refraction

Q1. If the image formed by a convex lens is of the same size as that of the object. What is the position and nature of the image with respect to the lens?

 Ans :  The image will be real, inverted and will be formed at centre of curvature of the lens.

Q2. What should be the position of the object, when a concave mirror is to be used:

(i)             as a shaving mirror, and

(ii)           in torches producing parallel beam of fight?

(b) A man standing in front of a mirror finds his image having a very small head and legs of normal size. What type of mirror are used in designing such a mirror?

(a)  (i) Face must be placed in between the pole and focus of the mirror so that enlarged, erect image of face can be formed.

(ii) At focus, because rays coming from the focus after reflection will become parallel.

(b)  It is a combination of convex mirror (small head) and plane mirror (legs of normal size).

Q3. An object is placed at the following distances from a concave mirror of focal length 15 cm.

(a) 10 cm

(b) 20 cm

(c) 30 cm

(d) 40 cm

Which position of the object will produce:

(i)             Virtual image

(ii)           A diminished real image

(iii)         An enlarged real image

(iv)         An image of same size.

Ans :

Given, concave mirror of f= 15 cm.

a. When object is placed at a distance 10 cm from mirror (between P and f) image is virtual, enlarged and erected.

b. For object in between 2F and 3 i.e. 40 cm image is inverted, diminished and real.

c. For object in between F and C (20 cm), image is inverted, enlarged and real beyond 2F(C).

d. For object at 2F (30 cm), the image is of same size.

Q4. (a) What is meant by refraction of fight?

(b) If on applying Cartesian sign convention for spherical lenses, the image distance obtained is negative, state the significance of the negative sign.

Ans:

(a) When a ray of light passes from one medium to another it bends from its path. The phenomenon of bending a ray of light when it passes from one medium to another is called refraction of light.

(b) In a lens if the image distance is negative then its meaning is that image formed is at the same side of object, virtual and erect. The lens is concave lens.

Q5. Differentiate between reflection and refraction of light.

Ans

Q6. What is meant by power of a lens? Give its SI unit. When two or more lenses are placed in contact, what will their combined power?

Ans : Power of a lens is the ability of the lens to converge or diverge a ray of light incident on it. It is the reciprocal of the focal length of the lens, i.e. P = 1/f. The SI unit of power is D(dioptre) if f is measured in metre.

Q7. How can you identify the three types of mirrors without touching them?

Ans : a. If the image formed is erect, of same size, and at equal distance behind the mirror as object and is in front of the mirror, then mirror is plane.

b. If the image is of larger size and erect and changes to inverted and smaller size by changing the position of mirror from the object it is concave mirror.

c. If the image is smaller and erect for all positions of mirror from the object, it is a convex mirror.

Q8. State the laws of reflection.

Ans : Laws of Reflection a. The incident ray, the reflected ray and the normal at the point of incidence are always in the same plane.

 b. <i = <r

Q9. (a) Name the spherical mirror used as:

1. Shavingmirror,

 2. Rearview mirror in vehicles,

3. Reflector in search – fights.

(b) Write any three differences between a real and virtual image.

Ans:

1. Concave mirror,

2. Convex mirror,

3. Concave parabolic

(b)

 Q10. What is meant by radius of curvature of a spherical mirror? How is it related to the focal length of the mirror?

Ans : Radius of curvature of a spherical mirror is the radius of the sphere of which mirror is a part. It is the distance between pole and centre of curvature of a mirror. The radius of curvature is equal to the twice the focal length R