Image Formation by Convex Lens

Q.

Draw ray diagrams showing the image formation by a convex lens when an object is placed

(a) between optical centre and focus of the lens
(b) between focus and twice the focal length of the lens
(c) at twice the focal length of the lens
(d) at infinity
(e) at the focus of the lens

Q.

The focal length of a convex lens is

Q. 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.

Define the optical centre of a spherical lens.

Q. Why real image is always inverted and virtual image is always erect?

Q. Concave lens always produces virtual image and convex lens always produces real image.

1. True
2. False

Q. The radii of curvature of the faces of a double concave lens are 10 cm and 15 cm.If focal length is 12 cm. What is the refractive index of glass?

Q. For which position of the object does a convex lens form a virtual and erect image?

1. At second focus (2F)
2. Between focus and pole​
3. At infinity
4. At focus (F)​

Q.

An object is placed at a distance of $\frac{f}{2}$ from a convex lens. The image will be formed:

1. At $-f$, virtual and double its size.

2. At $f$, real and inverted.

3. At $-2f$, virtual and erect.

4. At $2f$, real and erect.

Q. Magnification formula for lens in terms of focal length

Q.

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.

The convex lens always forms a real image.

1. True

2. False

Q. An object is placed at a distance 40 cm from a thin converging lens of focal length 10cm. Calculate the image distance.

1. $\frac{40}{3}cm$
2. $-\frac{40}{3}cm$
3. $\frac{20}{3}cm$
4. $-\frac{20}{3}cm$

Q. The characteristic(s) of an image formed by the convex lens when the object is placed between focus and optical centre is/are:

1. Real and inverted
2. Virtual and erect
3. Magnified
4. Diminished

Q. A point source of light is kept at a distance of 15 cm from a converging lens, on its optical axis. The focal length of the lens is 10 cm and its diameter of aperture is 3 cm. A screen is placed on the other side of the lens, perpendicular to the axis of the lens, at a distance 20 cm from it. Find the area of the illuminated part of the screen.

Q.

Which physical quantity does the unit diopter represent?

1. The power of the lens

2. The radius of curvature of the lens

3. The focal length of the lens

4. Twice the focal length of the lens

Q.

The diagram in figure shows the position of an object OA in relation to a convergin lens L whose foci are at $F_{1}and{F}_2$.

(i) Draw two rays to locate the position of image.

(ii) State the position of image with reference to the lens.

(iii) Describe three characteristics of the image.

(iv) Describe how the distance of image from the lens and its size change as the object as the object is moved towards $F_1$.

Q. The distance between optical centre and is known as focal length of the lens.

1. principal focus
2. centre of curvature
3. aperture

Q.

Name the lens which can concentrate sun's rays to a point-and burn a hole in a piece of paper.

Q.

State the condition when a lens is called an equiconvex or equi-concave.

Q. The magnification produced by a spherical lens is $+2.5$. What is type of lens used and the nature of the image formed ? Assume a normal object.

1. Concave, virtual and erect
2. Convex, real and erect
3. Convex, virtual and erect
4. Concave, real and inverted

Q. In a convex lens when the objects is placed , the image formed is real, inverted and diminished.

1. at $F_1$
2. at 2$F_1$
3. beyond 2$F_1$

Q.

A convergent beam of light passes through a diverging lens of focal length 0.2 m and comes to focus 0.3 m behind the lens. Find the position of the point at which the beam would converge in the absence of lens.

1. 0.22 m

2. 0.12 m

3. 0.1 m

4. 0.2 m

Q.

Describe in brief how would you determine the approximate focal length of a convex lens.

Q. A convex lens of focal length $10\text{cm}$ in contact with a concave lens of focal length $20\text{cm}$. This combination is used to focus an object positioned $30\text{cm}$ infront of combination. The image will be formed at a distance of

1. $30\text{cm}$
2. $40\text{cm}$
3. $50\text{cm}$
4. $60\text{cm}$

Q. If F1 and F2 represent the secondary focus and principal focus of the lens respectively, then the light rays meet at.

1. $F_1$
2. 2$F_1$
3. $F_2$
4. 2$F_2$

Q. The given figure shows an object AB, placed on the principal axis of a convex lens. $F_1$ and $F_2$ are the foci of lens Copy the diagram.

(a) Draw a ray of light from point B and passing through O. Show the same ray after refraction through the lens.
(b) Draw another ray from B, which passes through $F_2$, after refraction by the lens.
(c) Locate the final image formed.
(d) Is the image real or virtual?
(e) The image formed is inverted or erect?
[5 MARKS]

Q.

An object is placed 40 cm from a convex lens of focal length 20 cm. Calculate image distance.

1. v = 10 cm
2. v = 20 cm
3. v = 40 cm
4. v = 60 cm

Q. Where should an object be placed so that a virtual and erect image of enlarged size is obtained by a convex lens?

1. At f
2. Between f and 2f
3. At infinity
4. Between f and pole

Q. When an object is at a distance u1and u2 from a lens, real image and a virtual image is formed respectively having same magnification. The focal length of the lens is