# NCERT Solutions for Class 10 Science Light Reflection and Refraction Part 1

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NCERT solutions for Class 10 Science Light Reflection and Refraction

## NCERT Class 10 Science Chapter wise Solutions

• 1 – Chemical Reactions and Equations
• 2 – Acids, Bases and Salts
• 3 – Metals and Non-metals
• 4 – Carbon and Its Compounds
• 5 – Periodic Classification of Elements
• 6 – Life Processes
• 7 – Control and Coordination
• 8 – How do Organisms Reproduce?
• 9 – Heredity and Evolution
• 10 – Light Reflection and Refraction
• 11 – Human Eye and Colourful World
• 12 – Electricity
• 13 – Magnetic Effects of Electric Current
• 14 – Sources of Energy
• 15 – Our Environment
• 16 – Management of Natural Resources

## NCERT Solutions for Class 10 Science Light Reflection and Refraction Part 1

###### 1. Define the principle focus of a concave mirror.

Ans. Principal focus of a concave mirror is the point on its principal axis, where light rays coming parallel to principal axis actually converge after reflection from mirror.

###### 2. The radius of curvature of a spherical mirror is 20 cm. what is its focal length?

Ans. Focal length (f)= R/2 = 20 cm/2 = 10 cm.

###### 3. Name a mirror that can give an erect and enlarged image of an object.

Ans. Only a concave mirror can give a erect and enlarged image of an object.

###### 4. Why do we prefer a convex mirror as a rear-view mirror in vehicles?

Ans. We prefer a convex mirror as a rear-view mirror in vehicles because a convex mirror gives an erect and diminished image. As a result, convex mirror help the driver to have much wider field view.

Page No. 171

###### 1. Find the focal length of a convex mirror whose radius of curvature is 32 cm.

Ans. Radius of curvature of (R) = 32 cm

Focal length(f) = R/2 = 32/2 cm = 16 cm.

###### 2. A concave mirror produces three times magnified real image of an object placed at 10 cm in front of it. Where is the image located?

Ans. Distance of object from concave mirror (u)= -10 cm.

Magnification (m) = -3

m = -v/u

v = -mu = -(3) x (-10) = -30 cm.

Page No. 176

###### 1. A ray of light traveling in air enters obliquely into water. Does the light ray bend towards or away from the normal? Why?

Ans. The light bends towards the normal on entry into water. It is due to the fact that as compared to air, the water is optically denser medium.

###### 2. Light enters from air to glass having refractive index 1.50. What is the speed of light in glass? The speed of light in vacuum is 3×108 m/s.

Ans. Speed of light in vacuum (c) = 3 x 108 m/s.

Refractive index = c/v.

Speed of light in glass = 3 x 108 m/s/ 1.50

= 2 x 108 m/s

###### 3. Find out, from Table (10.3), the medium having highest optical density. Also, find the medium with lowest optical density.

Ans. As per table, diamond has highest optical density (2.42). Medium with lowest optical density is air (1.0003)

###### 4. You are given kerosene, turpentine and water. In which of these does the light travel fastest? Use the information given in table 10.3

Ans. As the refractive index of water is least out of three substances, hence speed of light is maximum in water. So, light travels fastest in water.

###### 5. The refractive index of diamond is 2.42. What is the meaning of this statement?

Ans. It means that speed of light in diamond is 2.42 times slower than speed of light in air.

NCERT Solutions for Class 10 Science Light Reflection and Refraction Part 1

###### 1. Define 1 dioptre of power of lens.

Ans. One dioptre of is defined as the power of lens having a focal length of 1 m.

NCERT Solutions for Class 10 Science Light Reflection and Refraction Part 1

###### 2. A convex lens forms a real and inverted image of a needle at distance of 50 cm. from it. Where is the needle placed in front of the convex lens if the image is equal to the size of objects? Also, find the power of lens.

Ans. Image distance (v) = +50 cm, hi = ho

hi/ho = v/u

u = v x ho / hi

= 50 x ho / hi

= 50 cm.

Now,

u = -50 cm

v = + 50 cm.

f = ?

1/f = 1/v – 1/u

1/f = 1/50 + 1/50

f = + 25 cm. = 0.25 m

Power of lens (P) = 1/f

= 1/ 0.25 = + 4D.

NCERT Solutions for Class 10 Science Light Reflection and Refraction Part 1

###### 3. Find the power of a concave lens of focal length 2 m.

Ans. Focal length of concave lens = – 2 m.

P = 1/f = 1/ (-2m)

= -0.5 D

## NCERT Solutions for Class 10 Science

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