Class X Chapter 10 – Light - Reflection and Refraction Science
Question 1:
Define the principal focus of a concave mirror.
Answer:
Light rays that are parallel to the principal axis of a concave mirror converge at a specific
point on its principal axis after reflecting from the mirror. This point is known as the
principal focus of the concave mirror.
Question 2:
The radius of curvature of a spherical mirror is 20 cm. What is its focal length?
Answer:
Radius of curvature, R = 20 cm
Radius of curvature of a spherical mirror = 2 × Focal length (f)
R = 2f
Hence, the focal length of the given spherical mirror is 10 cm.
Question 3:
Name the mirror that can give an erect and enlarged image of an object.
Answer:
When an object is placed between the pole and the principal focus of a concave mirror,
the image formed is virtual, erect, and enlarged.
Question 4:
Why do we prefer a convex mirror as a rear-view mirror in vehicles?
Answer:
Convex mirrors give a virtual, erect, and diminished image of the objects placed in front
of them. They are preferred as a rear-view mirror in vehicles because they give a wider
field of view, which allows the driver to see most of the traffic behind him.
Page 1 of 17
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,Class X Chapter 10 – Light - Reflection and Refraction Science
Question 1:
Find the focal length of a convex mirror whose radius of curvature is 32 cm.
Answer:
Radius of curvature, R = 32 cm
Radius of curvature = 2 × Focal length (f)
R = 2f
Hence, the focal length of the given convex mirror is 16 cm.
Question 2:
A concave mirror produces three times magnified (enlarged) real image of object placed
at 10 cm in front of it. Where is the image located?
Answer:
Magnification produced by a spherical mirror is given by the relation,
Let the height of the object, ho = h
Then, height of the image, hI = −3h (Image formed is real)
Object distance, u = −10 cm
v = 3 × (−10) = −30 cm
Here, the negative sign indicates that an inverted image is formed at a distance of
30 cm in front of the given concave mirror.
Page 2 of 17
Website: www.vidhyarjan.com Email: Mobile: 9999 249717
Head Office: 1/3-H-A-2, Street # 6, East Azad Nagar, Delhi-110051
(One Km from ‘Welcome Metro Station)
, Class X Chapter 10 – Light - Reflection and Refraction Science
Question 1:
A ray of light travelling in air enters obliquely into water. Does the light ray bend
towards the normal or away from the normal? Why?
Answer:
The light ray bends towards the normal.
When a ray of light travels from an optically rarer medium to an optically denser
medium, it gets bent towards the normal. Since water is optically denser than air, a ray
of light travelling from air into the water will bend towards the normal.
Question 2:
Light enters from air to glass having refractive index 1.50. What is the speed of light in
the glass? The speed of light in vacuum is 3 × 108 m s−1.
Answer:
Refractive index of a medium nm is given by,
Speed of light in vacuum, c = 3 × 108 m s−1
Refractive index of glass, ng = 1.50
Speed of light in the glass,
Question 3:
Find out, from Table, the medium having highest optical density. Also find the medium
with lowest optical density.
Material Refractive index Material medium Refractive
medium index
Air 1.0003 Canada Balsam 1.53
Ice 1.31 - -
Water 1.33 Rock salt 1.54
Alcohol 1.36 - -
Page 3 of 17
Website: www.vidhyarjan.com Email: Mobile: 9999 249717
Head Office: 1/3-H-A-2, Street # 6, East Azad Nagar, Delhi-110051
(One Km from ‘Welcome Metro Station)
Question 1:
Define the principal focus of a concave mirror.
Answer:
Light rays that are parallel to the principal axis of a concave mirror converge at a specific
point on its principal axis after reflecting from the mirror. This point is known as the
principal focus of the concave mirror.
Question 2:
The radius of curvature of a spherical mirror is 20 cm. What is its focal length?
Answer:
Radius of curvature, R = 20 cm
Radius of curvature of a spherical mirror = 2 × Focal length (f)
R = 2f
Hence, the focal length of the given spherical mirror is 10 cm.
Question 3:
Name the mirror that can give an erect and enlarged image of an object.
Answer:
When an object is placed between the pole and the principal focus of a concave mirror,
the image formed is virtual, erect, and enlarged.
Question 4:
Why do we prefer a convex mirror as a rear-view mirror in vehicles?
Answer:
Convex mirrors give a virtual, erect, and diminished image of the objects placed in front
of them. They are preferred as a rear-view mirror in vehicles because they give a wider
field of view, which allows the driver to see most of the traffic behind him.
Page 1 of 17
Website: www.vidhyarjan.com Email: Mobile: 9999 249717
Head Office: 1/3-H-A-2, Street # 6, East Azad Nagar, Delhi-110051
(One Km from ‘Welcome Metro Station)
,Class X Chapter 10 – Light - Reflection and Refraction Science
Question 1:
Find the focal length of a convex mirror whose radius of curvature is 32 cm.
Answer:
Radius of curvature, R = 32 cm
Radius of curvature = 2 × Focal length (f)
R = 2f
Hence, the focal length of the given convex mirror is 16 cm.
Question 2:
A concave mirror produces three times magnified (enlarged) real image of object placed
at 10 cm in front of it. Where is the image located?
Answer:
Magnification produced by a spherical mirror is given by the relation,
Let the height of the object, ho = h
Then, height of the image, hI = −3h (Image formed is real)
Object distance, u = −10 cm
v = 3 × (−10) = −30 cm
Here, the negative sign indicates that an inverted image is formed at a distance of
30 cm in front of the given concave mirror.
Page 2 of 17
Website: www.vidhyarjan.com Email: Mobile: 9999 249717
Head Office: 1/3-H-A-2, Street # 6, East Azad Nagar, Delhi-110051
(One Km from ‘Welcome Metro Station)
, Class X Chapter 10 – Light - Reflection and Refraction Science
Question 1:
A ray of light travelling in air enters obliquely into water. Does the light ray bend
towards the normal or away from the normal? Why?
Answer:
The light ray bends towards the normal.
When a ray of light travels from an optically rarer medium to an optically denser
medium, it gets bent towards the normal. Since water is optically denser than air, a ray
of light travelling from air into the water will bend towards the normal.
Question 2:
Light enters from air to glass having refractive index 1.50. What is the speed of light in
the glass? The speed of light in vacuum is 3 × 108 m s−1.
Answer:
Refractive index of a medium nm is given by,
Speed of light in vacuum, c = 3 × 108 m s−1
Refractive index of glass, ng = 1.50
Speed of light in the glass,
Question 3:
Find out, from Table, the medium having highest optical density. Also find the medium
with lowest optical density.
Material Refractive index Material medium Refractive
medium index
Air 1.0003 Canada Balsam 1.53
Ice 1.31 - -
Water 1.33 Rock salt 1.54
Alcohol 1.36 - -
Page 3 of 17
Website: www.vidhyarjan.com Email: Mobile: 9999 249717
Head Office: 1/3-H-A-2, Street # 6, East Azad Nagar, Delhi-110051
(One Km from ‘Welcome Metro Station)
