Short Answer Questions: Light: Mirrors and Lenses | Science Curiosity Class 8 - New NCERT PDF Download

Q1: Why the image formed by concave mirror is sometimes real, while sometimes virtual?

Ans: In case of concave mirror the image depends upon the distance of the object from the mirror. If the object is beyond the focus then real image is formed and if the object is closer than the focus then virtual image is formed
Q2: Why convex mirrors are used in vehicles?

Ans: Convex mirrors are used in vehicles because the image formed by convex mirror is always erect and smaller in size.
Q3: Explain the two laws of reflection.

Ans: There are two laws of reflection: the angle of incidence is equal to the angle of reflection and incident rays, reflected rays and normal rays drawn at the point of incidence to the reflecting surface lies in the same plane.

Q4: What kind of image is formed by a plane mirror?

Ans: Image formed by plane mirror is virtual, upright and of the same shape and size as of the object.
Q5: What do you mean by lateral inversion?

Ans: Lateral inversion is the reversal experienced by the image formed in a flat mirror. Although the image is the correct way up, its left and right sides are transposed.
Q6: What is incident ray?
Ans. The light ray, which strikes any surface is called the incident ray. 

Q7: What is reflected ray?
Ans. The ray that comes back from the surface after reflection is known as the reflected ray.

Q8: Define normal.
Ans. A perpendicular line on the mirror at the point where incident ray strikes is called normal.

Q9: Define angle of incidence.
Ans. The angle between the normal and incident ray is called the angle of incidence.

Q10: Define angle of reflection.
Ans. The angle between the normal and reflected ray is called angle of reflection.q 

Q11: Write the laws of reflection.
 Ans. There are two laws of reflection.
(i) Angle of incidence is equal to angle of reflection.
(ii) Incident ray, reflected ray and normal at the point of incidence, all lie in the same plane.

Q12: What is lateral inversion?
Ans. When an image is formed by a mirror the left of the object appears on the right and the right appears on the left, this is known as lateral inversion.

Q13: Define dispersion of light.
Ans. Splitting of light into its seven colours is known as dispersion of light.

Q14: Give an example of natural dispersion.
Ans. Rainbow is a natural phenomenon showing dispersion. 

Q15: What is the function of rods and cones in our eye?
Ans. Cones are sensitive to bright light and colour whereas rods are sensitive to dim light.
Q16: What is blind spot?
Ans. At the junction of the optic nerve and retina, there are no sensory cells, so no vision is possible at the spot. This is called the blind spot.

Q17: What is the function of eyelids.
Ans. Eyelids prevent any object from entering the eye. They also shut out light when not required. 

Q18: What is the Braille system?
Ans. Louis Braille developed a system for visually challenged persons. This is known as Braille system. He developed Braille code for common languages.

Q19: How many images of a mobile will be formed if it is placed between two parallel plane mirrors separated by 30 cm?

Ans: Infinite number of image will be formed if it is placed between two parallel plane mirrors .