Class 8 Science Chapter 13 Practice Question Answers - Light

Q1: Why fingers appear blurred when we move our hand very fast in front of our eyes?
Ans: This is due to persistence of vision l/16th of a second.

Q2: What makes things visible?
Ans: When light reaches our eyes after striking an object, we are able to see an object.

Q3: Which element is used at the back of plane mirror?
Ans: Silver

Q4: The distance between the object and its image formed by a plane mirror appears to be 18 cm. What is the distance between mirror and the object?
Ans: 9 cm

Q5: How is hypermetropia corrected?
Ans: It is corrected by using convex lens.

Q6: How is myopia corrected?
Ans: It is corrected by using concave lens.

Q7: A ray of light is incident on a mirror at an angle of 40°. What is the angle of reflect! u?
Ans: 40°

Q8: Name a device which works on the principle of multiple reflection.
Ans: Periscope

Q9: Light is a form of ___________.
Ans: energy

Q10: The ray of light which strikes the reflecting surface is called ___________.
Ans: incident

Q11: The bouncing back of light after it falls on a surface is called ___________.
Ans: reflection

Q12: A mirror has ___________ and ___________ surface.
Ans: smooth, polished

Q13: ___________ is the perpendicular line on the incidence point.
Ans: Normal

Q14: A plane mirror forms a ___________ image.
Ans: virtual

Q15: We are able to see an object due to the presence of
(a) light
(b) dark
(c) refraction
(d) object
Ans: (a)
Explanation: We are able to see objects because of light. When light from a source (such as the Sun or a light bulb) illuminates an object, the object reflects some of that light towards our eyes, allowing us to perceive it visually.

Q16: The bouncing back of light into the same medium is called
(a) refraction
(b) reflection
(c) dispersion
(d) diffraction
Ans: (b)
Explanation: Reflection is the process where light waves bounce back when they strike a surface. It can occur at various angles depending on the angle of incidence (angle between the incident ray and the normal) and the nature of the reflecting surface.

Q17: A mirror has _________ surface.
(a) rough
(b) polished
(c) dark
(d) all of these
Ans: (b)
Explanation: A mirror has a polished surface that is designed to provide a smooth and reflective surface. The reflective quality of the mirror comes from the way the surface is polished and coated with a thin layer of reflective material, such as aluminum or silver.

Q18: Maximum part of light is reflected by
(a) opaque object
(b) translucent object
(c) transparent object
(d) all of these
Ans: (c)
Explanation: The correct option should be (a) Opaque object. Opaque objects do not allow light to pass through them; rather, they absorb or reflect most of the light that strikes them. Therefore, maximum light is reflected by opaque objects.

Q19: Beam of light striking the reflecting surface is called
(a) incident ray
(b) reflected ray
(c) refracted ray
(d) normal ray
Ans: (a)
Explanation: The beam of light that strikes a reflecting surface is called the incident ray. It is the light ray that approaches the surface and strikes it, leading to reflection or other interactions with the surface.

Value-Based Questions

Q20: While playing, something entered into Somya’s eye. She immediately washed her eye with cold water. But as the irritation persisted, she immediately reported to her class teacher. Her class teacher took her to an eye doctor.

1. What should be done if some foreign particles enter your eyes?
2. Why is it not advised to rub your eyes when there is an eye irritation due to foreign particles?
3. Do you think Somya was right in her action?
4. What value of Somya is seen here?

Ans:

1. We must do the following things:
   • Restrict eye movement
   • Shut the eyelid
   • Do not rub eyes
   • Try to clean it with splash of clear water
   • Contact eye doctor immediately.
2. Foreign object may cause abrasions or scratches on our cornea or rubbing. It may also cause bleeding of cornea.
3. Yes.
4. She is intelligent, knowledgeable and aware of such kind of small accidents.