Here are clear and correct answers to your questions from the chapter Light — Reflection and Refraction (Class 10, NCERT, CBSE Board):
✅ Q1.
Which one of the following materials cannot be used to make a lens?
🎯 (d) Clay
Because clay is opaque, it does not allow light to pass through.
✅ Q2.
The image formed by a concave mirror is virtual, erect, and larger than the object. Where should be the position of the object?
🎯 (d) Between the pole of the mirror and its principal focus.
✅ Q3.
Where should an object be placed in front of a convex lens to get a real image of the same size as the object?
🎯 (b) At twice the focal length.
✅ Q4.
A spherical mirror and a thin spherical lens each have a focal length of –15 cm. The mirror and lens are likely to be:
🎯 (a) Both concave.
(negative focal length indicates concave mirror and concave lens)
✅ Q5.
No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be:
🎯 (d) Either plane or convex.
✅ Q6.
Which lens would you use while reading small letters in a dictionary?
🎯 (c) A convex lens of focal length 5 cm.
(Small focal length convex lens acts as a strong magnifier)
✅ Q7.
We wish to obtain an erect image of an object using a concave mirror of focal length 15 cm. What should be the range of distance of the object? What is the nature of the image?
- The object must be placed between the pole and focus (i.e., within 15 cm).
- The image is virtual, erect, and magnified.
- Ray diagram: 📐
(If you’d like, I can also generate the ray diagram in HTML or as an image.)
✅ Q8.
Type of mirror used in:
- (a) Headlights of a car — Concave mirror (produces a parallel beam of light)
- (b) Side/rear-view mirror of a vehicle — Convex mirror (provides wider field of view)
- (c) Solar furnace — Concave mirror (focuses sunlight at a point)
✅ Q9.
If one-half of a convex lens is covered, will it still produce a complete image?
✅ Yes.
Each part of the lens bends light rays from all parts of the object; however, the brightness of the image is reduced.
✅ Q10.
An object 5 cm long is held 25 cm away from a convex lens of focal length 10 cm.
- Using lens formula:
\frac{1}{v} - \frac{1}{u} = \frac{1}{f}
u = -25, f = +10
⇒ v = +16.7 cm - The image is real, inverted, and smaller than the object.
- Ray diagram: 📐 (can be provided on request)
✅ Q11.
Concave lens of focal length 15 cm forms an image at 10 cm. How far is the object?
- Lens formula:
\frac{1}{v} - \frac{1}{u} = \frac{1}{f}
v = -10, f = -15
Solving ⇒ u ≈ -30 cm - The object is placed at 30 cm.
- Ray diagram: 📐 (available on request)
✅ Q12.
Object at 10 cm from a convex mirror of focal length 15 cm.
- Mirror formula:
\frac{1}{v} + \frac{1}{u} = \frac{1}{f}
u = -10, f = +15
⇒ v ≈ +6 cm - Image is virtual, erect, and smaller.
✅ Q13.
Magnification of plane mirror is +1. What does it mean?
- The image is the same size as the object, virtual, and erect.
✅ Q14.
Object 5 cm, at 20 cm in front of a convex mirror of radius 30 cm.
- Radius R = 30 ⇒ f = 15 cm
- u = -20, f = +15
⇒ v ≈ +8.6 cm - Image is virtual, erect, smaller, size ≈ 2.15 cm.
✅ Q15.
Object of size 7 cm at 27 cm in front of a concave mirror of focal length 18 cm.
- u = -27, f = -18
⇒ v ≈ -54 cm - Screen should be placed at 54 cm.
- Image: real, inverted, magnified; size ≈ 14 cm.
✅ Q16.
Find the focal length of a lens of power –2.0 D. What type of lens?
- f = \frac{100}{P} = \frac{100}{-2} = -50 cm = –0.5 m
- Negative ⇒ concave lens
✅ Q17.
Doctor prescribes lens of power +1.5 D. Find focal length. What type of lens?
- f = \frac{100}{P} = \frac{100}{1.5} ≈ 66.7 cm = +0.667 m
- Positive ⇒ convex lens
📖 If you’d like, I can also prepare this as:
✅ A colorful HTML page with cards & colors
✅ A printable PDF with diagrams & ray drawings
✅ Or with ray diagrams drawn properly
✨ Would you like me to create that for you? Let me know!