Samacheer Kalvi 8th Science Unit 3 Book Back Answers:

Samacheer Kalvi 8th Standard New Science Book Back 1 Mark and 2 Mark Question & Answers PDF uploaded and available below. Class 8 New Syllabus 2021 to 2022 Book Back Question & Answer available for both English and Tamil Mediums. Class 8th Science Book Unit 3 – Light Answers/Solutions are provided on this page. 8th Std Science Book consists of 23 units, All Science Book Back One, and Two Mark Solutions are given below.

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Samacheer Kalvi 8th Science Book Back Solutions PDF:

8th Science Subject 1 Mark and 2 Mark Solutions PDF available below. Click the Download option to download the book back 1 Mark & 2 Mark questions and answers. Take the printout and use it for exam purposes. Samacheer Kalvi 8th Science Unit 3 Answers are given below.

Science Book Back Answers

Unit 3 – Light

I. Choose the best answer

1. Which of the following has curved reflecting surface –
(a) Plane mirrors
(b) Spherical mirrors
(c) Simple mirrors
(d) None of the above
Answer:
(b) Spherical mirrors

2. The spherical mirror with a reflecting surface curved inward is called –
(a) Convex mirror
(b) Concave mirror
(c) Curved mirror
(d) None of the above
Answer:
(b) Concave mirror

3. The spherical mirror used as a rear view mirror in the vehicle is –
(a) Concave mirror
(b) Convex mirror
(c) Plane mirror
(d) None of the above
Answer:
(b) Convex mirror

4. The imaginary line passing through the centre of curvature and pole of a spherical mirror is called –
(a) Centre of curvature
(b) Pole
(c) principal axis
(d) Radius curvature
Answer:
(c) principal axis

5. The distance from the pole to the focus is called –
(a) Pole length
(b) Focal length
(c) principal axis
(d) None of the above
Answer:
(b) Focal length

6. If the image and object distance is same, then the object is placed at –
(a) Infinity
(b) At F
(c) Between f and P
(d) At C
Answer:
(d) At C

7. If the focal length of a spherical mirror is 10 cm, what is the value of its radius of curvature?
(a) 10 cm
(b) 5 cm
(c) 20 cm
(d) 15 cm
Answer:
(c) 20 cm

II. Fill in the blanks

1. The spherical mirror used in a beauty parlour as make – up mirror is ………………
2. Geometric centre of the spherical mirror is ………………
3. Nature of the images formed by a convex mirror is ………………
4. The mirror used by the ophthalmologist to examine the eye is ………………
5. If the angle of incidence is 45°, then the angle of reflection is ………………..
6. Two mirrors are parallel to each other, then the number of images formed is ………………

Answer:

1. Concave mirror
2. pole
3. Smaller, virtual and erect
4. Concave mirror
5. 45°
6. Infinite

III. Match the following.

Answer:

1 – ii; 2 – i; 3 – iv; 4 – v; 5 – iii

IV. Answer in brief

1. Define focal length.
Answer:
The distance between the pole and the principal focus is called focal length (f) of a spherical mirror.

2. Give two applications of a concave and convex mirror.
Answer:
Concave mirrors:

1. Concave mirrors are used while applying make – up or shaving, as they provide a magnified image.
2. They are used in torches, search lights and head lights as they direct the light to a long distance.

Convex mirrors:

1. Convex mirrors are used in vehicles as rear view mirrors because they give an upright image and provide a wider field of view as they are curved outwards.
2. They are found in the hallways of various buildings including hospitals, hotels, schools and stores. They are usually mounted on a wall or ceiling where hallways make sharp turns.

3. State the laws of reflection.
Answer:

1. The incident ray, the reflected ray and the normal at the point of incidence, all lie in the same plane.
2. The angle of incidence and the angle of reflection are always equal.

4. Define the refractive index of a medium.
Answer:
The amount of refraction of light in a medium is denoted by a term known as refractive index of the medium, which is the ratio of the speed of light in the air to the speed of light in that particular medium.

5. State the Snell’s law of refraction.
Answer:
Refraction of light rays, as they travel from one medium to another medium, obeys two laws, which are known as Snell’s laws of refraction. They are:

1. The incident ray, the refracted ray and the normal at the point of intersection, all lie in the same plane.
2. The ratio of the sine of the angle of incidence (i) to the sine of the angle of refraction (r) is equal to the refractive index of the medium, which is a constant.

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