9. Light-Reflection and Refraction Science class 10 in English Medium ncert book solutions Additional Questions With Solutions

Extra Important Questions with Answers – Chapter 9: Light – Reflection and Refraction

Q1: What is reflection of light?

Ans: Reflection of light is the bouncing back of light into the same medium after striking a reflecting surface.

Q2: State the two laws of reflection of light.

Ans:

• The angle of incidence is equal to the angle of reflection.
• The incident ray, reflected ray, and the normal at the point of incidence lie in the same plane.

Q3: What is refraction of light?

Ans: Refraction is the bending of light when it passes from one transparent medium to another due to a change in its speed.

Q4: Why does light bend during refraction?

Ans: Light bends because its speed changes when it travels from one medium to another having a different optical density.

Q5: Define the principal focus of a concave mirror.

Ans: The principal focus of a concave mirror is the point on its principal axis where rays parallel to the principal axis meet after reflection.

Q6: Define the principal focus of a convex mirror.

Ans: The principal focus of a convex mirror is the point behind the mirror from which rays parallel to the principal axis appear to diverge after reflection.

Q7: What is the radius of curvature of a spherical mirror?

Ans: The radius of curvature is the distance between the pole and the centre of curvature of the mirror.

Q8: What is the relationship between the focal length and radius of curvature of a spherical mirror?

Ans: The focal length is half of the radius of curvature.

Q9: What is the pole of a spherical mirror?

Ans: The pole is the geometric centre of the reflecting surface of a spherical mirror.

Q10: What is the centre of curvature?

Ans: The centre of curvature is the centre of the sphere of which the mirror is a part.

Q11: What is magnification?

Ans: Magnification is the ratio of the height of the image to the height of the object.

Q12: What does a positive magnification indicate?

Ans: Positive magnification indicates that the image is virtual and erect.

Q13: What does a negative magnification indicate?

Ans: Negative magnification indicates that the image is real and inverted.

Q14: What type of image is formed by a plane mirror?

Ans: A plane mirror forms a virtual, erect image of the same size as the object.

Q15: Name the mirror used as a rear-view mirror in vehicles. Give one reason.

Ans: A convex mirror is used because it provides a wide field of view and always forms an erect, diminished image.

Q16: Which mirror is used by dentists? Why?

Ans: Dentists use a concave mirror because it forms a magnified, erect image of nearby teeth.

Q17: What is a lens?

Ans: A lens is a transparent optical device bounded by two curved surfaces or one curved and one plane surface that refracts light.

Q18: Differentiate between a convex lens and a concave lens.

Ans:

• A convex lens is thicker at the centre and converges light rays.
• A concave lens is thinner at the centre and diverges light rays.

Q19: Why is a convex lens called a converging lens?

Ans: It is called a converging lens because it brings parallel rays of light to a single point called the principal focus.

Q20: Why is a concave lens called a diverging lens?

Ans: It is called a diverging lens because it spreads parallel rays of light after refraction.

Q21: Define the power of a lens.

Ans: The power of a lens is its ability to converge or diverge light rays. It is the reciprocal of its focal length measured in metres.

Q22: What is the SI unit of power of a lens?

Ans: The SI unit of power is the dioptre (D).

Q23: Why is the power of a convex lens positive?

Ans: The power of a convex lens is positive because its focal length is positive.

Q24: Why is the power of a concave lens negative?

Ans: The power of a concave lens is negative because its focal length is negative.

Q25: What happens to a ray passing through the optical centre of a thin lens?

Ans: The ray passes through the optical centre without any deviation.

Q26: State any two differences between reflection and refraction.

Ans:

• Reflection is the bouncing back of light, whereas refraction is the bending of light.
• Reflection occurs in the same medium, whereas refraction occurs when light passes from one medium to another.

Q27: Why are spherical mirrors preferred over plane mirrors in many applications?

Ans: Spherical mirrors can converge or diverge light rays and are capable of forming enlarged or diminished images, making them useful in vehicles, telescopes, and medical instruments.

Q28: What are the uses of a concave mirror?

Ans:

• As shaving and makeup mirrors.
• By dentists for examining teeth.
• In headlights and searchlights.
• In solar furnaces.

Q29: What are the uses of a convex mirror?

Ans:

• As rear-view mirrors in vehicles.
• For surveillance in shops and parking areas.
• At road intersections to avoid accidents.

Q30: Why is understanding reflection and refraction important in daily life?

Ans: Reflection and refraction help in the working of mirrors, lenses, cameras, microscopes, telescopes, spectacles, projectors, and many other optical devices used in everyday life.

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