9. Light-Reflection and Refraction Class 10 Science [LATEST] Solutions Long Additional Questions With Solutions in english - CBSE Study

Long Additional Questions with Solutions – Chapter 9: Light – Reflection and Refraction

Q1. State the laws of reflection of light. Explain the formation of an image by a plane mirror with its characteristics.

Solution:

Reflection of light is the phenomenon in which light rays bounce back into the same medium after striking a reflecting surface.

Laws of Reflection:

• 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.

Image Formation by a Plane Mirror:

• The image is formed behind the mirror.
• It is virtual and erect.
• It is of the same size as the object.
• The image is laterally inverted.
• The image is formed at the same distance behind the mirror as the object is in front of it.

Q2. Explain the formation of images by a concave mirror for different positions of the object.

Solution:

A concave mirror can produce different types of images depending on the position of the object.

• Object at Infinity: Image forms at the focus; highly diminished, real and inverted.
• Beyond Centre of Curvature (C): Image forms between C and F; diminished, real and inverted.
• At Centre of Curvature (C): Image forms at C; same size, real and inverted.
• Between C and F: Image forms beyond C; enlarged, real and inverted.
• At Focus (F): Image forms at infinity; highly enlarged.
• Between Pole (P) and Focus (F): Image forms behind the mirror; virtual, erect and enlarged.

Q3. Describe the image formation by a convex mirror. Why is it used as a rear-view mirror?

Solution:

A convex mirror always forms an image behind the mirror.

• The image is always virtual and erect.
• The image is diminished.
• It provides a wide field of view.

Reason for Use as Rear-view Mirror:

• It allows the driver to see a larger area behind the vehicle.
• The image remains erect.
• It helps reduce blind spots and improves road safety.

Q4. Explain refraction of light. Why does light bend when it passes from one medium to another?

Solution:

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

When light travels from a rarer medium to a denser medium, its speed decreases and it bends towards the normal. When it travels from a denser medium to a rarer medium, its speed increases and it bends away from the normal.

Applications of Refraction:

• Formation of images by lenses.
• Working of cameras and microscopes.
• Optical fibres.
• Human eye.

Q5. Explain the structure, working and uses of a convex lens.

Solution:

A convex lens is thicker at the centre and thinner at the edges.

It converges parallel rays of light to a point called the principal focus.

Image Formation:

• Produces real and inverted images when the object is beyond the focus.
• Produces a virtual, erect and magnified image when the object is between the focus and the optical centre.

Uses:

• Magnifying glass.
• Microscopes.
• Telescopes.
• Cameras.
• Correcting hypermetropia.

Q6. Explain the structure, working and uses of a concave lens.

Solution:

A concave lens is thinner at the centre and thicker at the edges.

It diverges parallel rays of light, making them appear to originate from the principal focus.

Characteristics of Image:

• Always virtual.
• Always erect.
• Always diminished.

Uses:

• Correcting myopia.
• Door viewers (peepholes).
• Optical instruments.

Q7. What is magnification? Derive the expression for magnification produced by mirrors and lenses.

Solution:

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

For Mirrors:

Magnification (m) = Height of Image / Height of Object = –v/u

For Lenses:

Magnification (m) = Height of Image / Height of Object = v/u

Significance:

• Positive magnification indicates a virtual and erect image.
• Negative magnification indicates a real and inverted image.
• |m| > 1 means enlarged image.
• |m| < 1 means diminished image.

Q8. Explain the concept of power of a lens. State its SI unit and significance.

Solution:

The power of a lens measures its ability to converge or diverge light rays.

It is equal to the reciprocal of the focal length (in metres).

SI Unit: Dioptre (D)

Significance:

• A convex lens has positive power.
• A concave lens has negative power.
• A lens with shorter focal length has greater power.
• Power is used in prescribing spectacles.

Q9. Differentiate between a concave mirror and a convex mirror.

Solution:

Concave Mirror	Convex Mirror
Reflecting surface curves inward.	Reflecting surface curves outward.
Can form real or virtual images.	Always forms virtual images.
May produce enlarged images.	Always produces diminished images.
Used in shaving mirrors and headlights.	Used as rear-view mirrors.

Q10. Differentiate between a convex lens and a concave lens.

Solution:

Convex Lens	Concave Lens
Thicker at the centre.	Thinner at the centre.
Converges light rays.	Diverges light rays.
Focal length is positive.	Focal length is negative.
Used to correct hypermetropia.	Used to correct myopia.
Can form real or virtual images.	Always forms virtual, erect and diminished images.