# Magnification by Thin Lenses

## Trending Questions

**Q.**

A concave mirror of focal length 20 cm produces an image twice the height of the object.if the image is real, then distance of the object from the mirror is

1. 20cm.

2. 60cm.

3. 10cm.

4. 30cm

**Q.**

In a convex lens of focal length F, the minimum distance between an object and it's real image must be?

a) 3F b) 4F c) 3/2F d) 2F

**Q.**A telescope has a objective of focal length 50 cm and an eye-piece of focal length 5 cm. The least distance of distinct vision is 25 cm. The telescope is focused for distinct vision on a scale of 200 cm away. The separation between the objective and the eye-piece is

- 74 cm
- 60 cm
- 71 cm
- 75 cm

**Q.**The size of image of an object which is at infinity is formed by a convex lens of focal length 30 cm is 2 CM if a concave lens of focal length 20 cm is placed between the convex lens and the image at distance of 26 m from the convex lens calculate the new size of image

**Q.**A short linear object of length l lies along the axis of a concave mirror at a distance u from it. If v is the distance of the image from the mirror, then the size of the image is

- (vu)2l
- (uv)l
- (vu)l
- (uv)2l

**Q.**36.A 2-cm-high object is placed at a distance of 32cm from a concave mirror. The image is real, inverted and 3cm in size. Find the focal length of the mirror and the position of the image.

**Q.**

A concave mirror forms an image of 20 cm high object on a screen placed 5.0 m away from the mirror. The height of the image is 50 cm. Find the focal length of the mirror and the distance between the mirror and the object.

**Q.**An object is placed beyond the principal focus at a distance of 9 cm from it in front of a concave mirror on the principal axis. The image is formed beyond the principal focus at a distance of 16 cm from the principal focus. The focal length of the mirror is

- 12 cm
- 11 cm
- 13 cm
- 10 cm

**Q.**

True or false: Maximum zoom percentage in word document is 500

**Q.**57.A convex lens forms a real image 9 cm long on a screen. Without altering the position of the object and the screen, the lens is displaced and we get again a real image 4 cm long on the screen. Then the length of the object is :- (1) 9cm (2) 4cm (3) 6cm (4) 36cm Click here to view details:

**Q.**The magnetic field of a beam emerging from a filter facing a floodlight is given by B0 = 12×10−8sin (1.20×107z −3.60×1015t)T. What is the average intensity of the beam?

**Q.**A convex lens produces an image of an object on a screen with a magnification of 1/2.When the lens is moved 30 cm away from the object, the magnification of the image is 2. The focal length is (1)20 cm (2) 25 cm (3)30cm (4) 35

**Q.**

An object is placed 15 cm in front of a convex lens of focal length 10 cm. Find the nature and position of the image formed. Where should a concave mirror of radius of curvature 20 cm be placed so that the final image is formed at the position of the object itself?

**Q.**

A point object is projected from the principle axis in front of convex lens of focal length 12 cm as shown in figure then

- Speed of image along principle axis is 7 m/s
- Speed of image perpendicular to principle axis is 4 m/s
- Angle that velocity of image makes with principle axis is greater than 45∘
- Image of object moves away from lens

**Q.**72.For two different positions of a thin convex lens between a real thin, erect object and the screen, the length of images formed are 18 cm and 8 cm respectively. The length of the object is 1) 10 cm 2) 12 cm 3) 13 cm 4) 14 cm

**Q.**

The focal length of the lens of a myopic person is $40cm$. What is the power of the lens?

**Q.**

**Assertion :** X-rays are used for studying the structure of crystals.

**Reason :** Size of the atoms of crystals is of the order of wavelength of X-rays.

If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion

If both Assertion & Reason are True & the Reason is not a correct explanation of the Assertion

If Assertion is True but the Reason is False

If both Assertion & Reason are false

**Q.**A concave mirror of focal length 40cm forms a real image of an object of size 3 times size of object. Find out position of both object and image.

**Q.**

A particle executes a simple harmonic motion of amplitude 1.0 cm along the principal axis of a convex lens of focal length 12 cm. The mean position of oscillation is at 20 cm from the lens. Find the amplitude of oscillation of the image of the particle.

**Q.**

A convex lens produces a real image m times the size of the object. What is the distance of the object from the lens?

**Q.**

A convex lens of focal length f1 is kept in contact with a concave lens of focal length f2. Find the focal length of the combination.

**Q.**a concave mirror of focal length 20cm is placed at a dis†an ce of 50cm from a wall. how far from the wall should an object be placed to form its real image on the wall

**Q.**147.When an object is placed 20 cm from a concave mirror, a real image magnified three times is formed. Find a.) find the focal length of the mirror b.) where must the object be placed to give a virtual image three times the height of the object.

**Q.**

The far point of a myopic person is $75\mathrm{cm}$ in front of the eye. What is the nature and power of the lens required to correct the problem?

**Q.**

A slide projector has to project a 35 mm slide (25 mm×23 mm) on a 2m×2m screen at a distance of 10 m from the lens. What should be the focal length of the lens in the projector ?

**Q.**

In a Michelson experiment for measuring speed of light, the distance travelled by light between two reflections from the rotating mirror is 4.8 km. The rotating mirror has a shape of a regular octagon. At what minimum angular speed of the mirror (other than zero) the image is formed at the position where a nonrotating mirror forms it?

**Q.**For the system shown in the figure, the position of the final image of object O is

[Assume origin of co-ordinate system to be at optical centre of half convex lens]

- (x=60 cm, y=−6 mm)
- (x=60 cm, y=−10 mm)
- (x=30 cm, y=−6 mm)
- (x=30 cm, y=−10 mm)

**Q.**A screen is placed at a distance of 100cm from an object. The image of the object is formed on the screen by a convex lens for two different locations of a lens seperated by 20cm. Calculate the focal length of the lens used.

**Q.**

The ratio of the size of the image to the size of the object

**Q.**9.Size of image of an object by a mirror having a focal length of 20 cm is observed to be reduced to 1/3rd of its size. At what distance the object has been placed from the mirror? What is the nature of the image and the mirror?