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

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:

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

Solution:

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