Convex Lens

Q. The focal lengths of the lenses of an astronomical telescope are 50 cm and 5 cm. The length of the telescope when the image is formed at the least distance of distinct vision is

1. 45 cm
2. 55 cm
3. $\frac{275}{6}cm$
4. $\frac{325}{6}cm$

Q.

How are converging lenses different from diverging lenses?

Q. An object is placed at 30 cm in front of a convex lens of focal length 20 cm. Find the position of the image. What is the magnification of the object?
[4 MARKS]

Q. Why is the focal length of a thick lens less and a thin lens more?

Q.

The lens which can produce a real and inverted image of an object is /are

1. Convex lens

2. Concave Lens

3. Convex and Concave lens

4. Plano-concave lens

Q. By drawing ray diagrams, discuss the characteristics of the image formed by a convex lens when the object is:
(a) between the optical centre and the focus.
(b) at the focus.
(c) at $2F_1$.
(d) at infinity.
[5 MARKS]

Q. A candle placed 25 cm from a lens, forms an image on a screen placed 75 cm on the other end of the lens. The focal length is + 18.75 cm and is a convex lens.

1. True
2. False

Q.

A double convex air bubble in water will act as

1. convex lens

2. concave mirror

3. convex mirror

4. concave lens

Q. In a concave lens, when an object is between infinity and the optical centre (O), an image is formed between the .

1. focus (F${}_1$) and optical centre (O)
2. focus (F${}_1$) and 2F${}_1$

Q. A virtual, diminished image is formed when an object is placed between the optical centre and the principal focus of a lens.
(i) Name the type of lens which forms the above image.
(ii) Draw a ray diagram to show the formation of the image with the above stated characteristics.

Q. Figure 5.49 shows an object AB placed on the principal axis of a lens L. The two foci of the lens are $F_1$ and $F_2$. The image formed by the lens is erect, virtual and diminished. Copy the diagram.

(a) What type of lens is it?
(b) Draw the outline of the lens (L) used.
(c) Draw a ray of light starting from B and passing through O. Show the same ray after refraction through the lens.
(d) Draw another ray from B, which after passing parallel to the principal axis, is incident on the lens and emerges after refraction from it. (d) Locate the final image formed.
[5 MARKS]

Q. Give two uses of convex lens.

Q.

Find the angle of refraction in the following figure?

1. ${45}^{\circ }$

2. ${20}^{\circ }$

3. ${30}^{\circ }$

4. ${65}^{\circ }$

Q. Question 7
A beam of light is incident through the holes on side A and emerges out of the holes on the other face of the box as shown in the figure. Which of the following could be inside the box?


(a) Concave lens
(b) Rectangular glass slab
(c) Prism
(d) Convex lens

Q. Which of the following lenses of appropriate focal length is used to correct shortsightedness ?

1. Concave
2. Convex
3. None of the above
4. Both A & B

Q. In sun glasses, both of its surface are curved, yet their behaviour is neither like a convex lens nor like a concave lens. State the reason.

Q. A concave lens; doesn't have a focus because

1. Both it's surfaces are concave
2. It doesn't converge a parallel beam of light falling on it on a single point.
3. It has a focus; where all the diverging rays appear to meet.
4. Can't comment

Q. Convex lens has a focal length and concave lens has a focal length.

1. positive
2. negative
3. zero
4. inverse

Q. Why is a convex lens called a converging lens and a concave lens a diverging lens? [3 MARKS]

Q. (i) Mirror used by a dentist(ii) Mirrors on the sides of car 60(iii) Floodlights(iv) Solar devices having mirrors
Concave mirror Convex mirror

Q. The parallel rays of light after passing through a convex lens converge at:

1. Principal focus
2. Centre of curvature
3. Optical centre
4. Infinity

Q. The focal length of convex lens is $2.5cm$. Its magnifying power for minimum distance of distinct vision will be:

1. $25$
2. $52$
3. $11$
4. $1.1$

Q. Imagine if there is a convex lens which is made of a material whose optical density is less than that of the air, it would still act as:

1. plane mirror
2. diverging lens
3. converging lens
4. can't be said

Q.

If there is a convex lens which is made of material whose optical density is less than that of air, then it would be a converging lens.

1. False

2. True

Q.

Question 9
One-half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.

Q. Question 7
A beam of light is incident through the holes on side A and emerges out of the holes on the other face of the box as shown in the figure. Which of the following could be inside the box?


(a) Concave lens
(b) Rectangular glass slab
(c) Prism
(d) Convex lens

Q. A lens can be considered to be made up of a combination of different sections of ______.

1. Mirror
2. Prism
3. Glass slab
4. Hollow glass cylinder

Q.

A combination of $3$ convex lenses is made. The focal length of lens I is $+5cm$, lens II is $+10cm$ and lens III is $+20cm$. Calculate the total power of the combination in dioptre?

1. 35

Q. The nature of the image formed by a convex lens when the object is placed beyond the centre of curvature ($2F_1$) is:

1. Real, inverted
2. Virtual, erect
3. Real, erect
4. Virtual, inverted

Q. A convex lens of focal length 40 cm is placed 20 cm away from another convex lens of focal length 50 cm. A candle is placed 60 cm in front of the first lens. Find the distance between the final image and the first lens.