# Lens Formula and Magnification

## Trending Questions

**Q.**

A concave lens of focal length $15cm$ forms an image $10cm$ from the lens. How far is the object placed from the lens? Draw the ray diagram.

**Q.**

All formulas from the 'Light' chapter.

**Q.**

A concave lens has focal length 15 cm. At what distance should the object from the lens should be placed so that it forms an image at 10 cm from the lens? Also find the magnification produced by the lens.

**Q.**

A concave mirror has a focal length of 4 cm and an object 2 cm tall is placed 9 cm away from it. Find the nature and position of the image formed.

**Q.**Find the size , nature and position of image formed when an object of size 1 cm is placed at a distance of 15 cm from a concave mirror of focal length 10 cm

**Q.**

An object is placed at a distance of 20 cm from a convex mirror of a focal length of 15 cm. Find the position and nature of the image.

**Q.**

What is the magnification produced by a rear-view mirror fitted in a vehicle?

Equal to 1

More than 1

Less than 1

Can be either more or less than 1, depending on the position of the object in front of it.

**Q.**

A student focuses the image of a candle flame on a white screen using a convex lens. He noted down the position of the candle screen and the lens as shown below

Position of candle = 12.0 cm

Position of convex lens = 50.0 cm

Position of the screen = 88.0 cm

(i) What is the focal length of the convex lens?

(ii) Where will the image be formed if he shifts the candle towards the lens at a position of 31.0 cm?

(iii) What will be the nature of the image formed if he further shifts the candle towards the lens?

(iv) Draw a ray diagram to show the formation of the image in case (iii) as said above.

**Q.**

The filament of a lamp is 80 cm from a screen and a converging lens forms an image of it on a screen, magnified three times. Find the distance of the lens from the filament and the focal length of the lens.

**Q.**

Calculate the image distance for an object of height 12 mm at a distance of 0.20 m from a concave lens of focal length 0.30 m, and state the nature and size of the image.

**Q.**

An object 4 cm high is placed at a distance of 10 cm from a convex lens of focal length 20 cm. Find the position, nature and size of the image.

**Q.**An object of 5cm size is placed at a distance of 20cm from a converging mirror of focal 15cm. At what distance from the mirror should a screen be placed to get a sharp image? Also calculate the size of the image?

**Q.**

An object 2.4 m in front of a lens forms a sharp image on a film 12 cm behind the lens. a glass plate 1 cm thick, of refractive index 1.50 is interposed between lens and films with its plane faces parallel to film. at what distance (from the lens) should the object be shifted to be in sharp focus on film?

**Q.**

If the magnification of a body of size 1 m is 2, what is the size of the image ?

**Q.**A convex lens of focal length 40cm is in contact with a concave lens of focal length 25cm. The power of the combination is

- -1.5 D
- -6.5 D
- +6.5 D
- + 1.5 D

**Q.**

Determine how far an object must be placed in front of a converging lens of focal length 10 cm in order to produce an erect (upright) image of linear magnification 4.

**Q.**

Why we use minus sign in the formula of magnification of mirror?

m= -v/u

**Q.**

An object is placed at a distance of 10 cm from a convex mirror of focal length 5 cm. (i) Draw a ray-diagram showing the formation of image. (ii) State two characteristics of the image formed. (iii) Calculate the distance of the image from mirror.

**Q.**

A lens forms an image of an object which is placed at a distance 15 cm in front of it. if the image forms at a distance 60 cm on the same side Find : (i) the focal length, (ii) the magnification, and (iii) the nature of image.

**Q.**

An object 60 cm from a lens gives a virtual image at a distance of 20 cm in front of the lens. What is the focal length of the lens ? Is the lens converging or diverging ? Give reasons for your answer.

**Q.**

An object is placed at a distance of 6 cm from a convex mirror of focal length 12 cm. Find the position and nature of the image.

**Q.**

Find the position and nature of the image of an object 5 cm high and 10 cm in front of a convex lens of focal length 6 cm.

**Q.**

When do u take image distance positive or negative?

When do u take object distance negative or positive?

Plzz explain it in detail

**Q.**

A convex lens produces an inverted image magnified three times of an object placed at a distance of 15 col from it. Calculate focal length of the lens.

**Q.**Choose the correct option.

Convex lens has negative focal length and concave lens has a positive focal length.

Convex lens has positive focal length and concave lens has a negative focal length.

Both convex lens and concave lens have a negative focal length.

Both convex lens and concave lens have a positive focal length.

**Q.**

An erect image 2.0 cm high is formed 12 cm from a lens, the object being 0.5 cm high. Find the focal length of the lens.

**Q.**

A 50 cm tall object is at a very large distance from a diverging lens. A virtual, erect and diminished image of the object is formed at a distance of 20 cm in front of the lens. How much is the focal length of the lens ?

**Q.**

An object 50 cm tall is placed on the principal axis of a convex lens. Its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens.

**Q.**

A dentist uses a small concave mirror of focal length of 3 cm and holds it at a distance of 2 cm from the tooth. Which of the following statement is incorrect about the image formed?

a) The image is three times the size of the object.

b) The image distance is 6 cm from the pole.

c) The image formed is erect.

d) The distance between the object and the image is 8 cm.

e) None of the above

**Q.**

List 4 characterestcha of image formed by concave mirror