Sign Convention for Lens

Q.

An object is situated at a distance of f/2 from a convex lens of focal length f. Distance of image will be

1. -f

2. -(f/2)

3. +(f/3)

4. +(f/4)

Q.

The focal length of a concave lens is:

1. negative when image formed is real

2. always positive

3. always negative

4. positive when image formed is real

Q. Which of the following is true about concave lenses?

1. Focal length is positive
2. Image distance can be positive or negative
3. Height of image can be positive or negative
4. Image distance is always negative

Q. For a concave lens, if the magnification has a plus sign, then image is _________ .

1. real and inverted
2. virtual and erect
3. virtual and inverted
4. real and erect

Q. Is it true that, if focal length of a convex lens is positive then the image is formed'v' is also positive?

Q. (a) The ray diagram given below illustrates the experimental set-up for the determination of the focal length of a converging lens using a plane mirror.

(i) Write two characteristics of the image Formed.
(ii) What is the name given to the distance between the object and optical centre of the lens in the above diagram?
(b) The given figure shows an object O as its image I. Copy the diagram and draw suitable rays to locate the lens and focus. Name the type of lens in this cases

[5 MARKS]

Q. In lenses, all the distances are measured from optical centre of the lens as a convention.

1. False
2. True

Q. An object is placed at a certain distance from a convex lens of focal length 20 cm. Find the distance of the object if the image obtained is magnified 4 times.

Q. The magnification of an object placed in front of a convex lens of focal length 40 cm is +4. To obtain a magnification of –4, the object will have to be moved by a distance equal to

40 cm फोकस दूरी के एक उत्तल लेन्स के सामने रखी एक वस्तु का आवर्धन +4 है। –4 आवर्धन प्राप्त करने के लिए, वस्तु को कितनी दूरी तक गति करानी होगी?

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

Q. A convex lens forms a real and inverted image. The magnification will be .

1. positive
2. negative
3. zero

Q. A small luminous object is placed at a distance of 48xn from a convex lens of focal length 30cm on its principal axis. A concave lens of focal length 60cm is placed coaxially on the other side of the lens at a distance of X cm from it .If a real image is formed by the combination at a point 1.6 m from the convex lens then the value of X is

Q.

What is lens formula and derivation

Q. A concave lens of 20 cm focal length forms an image 15 cm from the lens. Compute the object distance.

Q. When a real image is cast by a lens, the magnification produced by it is.

1. positive
2. negative
3. zero

Q.

How the focal length can be positive on left side of the same side of the object

Q. In lenses, all the distances are measured from optical centre of the lens as a convention.

1. False
2. True

Q. Calculate the focal length of a convex lens which produces a virtual image at a distance of 50 cm of an object placed 20 cm in front of it.

Q. ntA planoconvex lens of refractive index 1.5 and radius of curvature 30 cm , is silvered at the curved surface.Now this lens has been used to form the image of an object.At what distance from this lens an object be placed in order to have a real image of the size of the objectn nta)20 cmn ntb)30 cmn ntc)60 cmn ntd)80 cmn

Q.

Draw ray diagram showing the image formation by a converging lens with when an object is placed at infinity.

Q. According to the sign convention for lenses, the object distance from the lens (u) must always be taken as .

1. positive
2. negative
3. zero

Q. An object is 2 m from a lens which forms an erect image one-fourth (exactly) the size of the object. Determine the focal length of the lens. What type of lens is this?

Q. Distance of an actual object is always as per cartesian sign convention.

1. positive
2. negative
3. zero

Q. According to the sign conventions, focal length of a concave lens is _____.

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

Q. An object is placed at principal axis of a concave lensat a distance of 20cm fromit andif thefocal length of thelensis also 20cm, find thelocation of the image

Q. Minimum number of rays required to form an image of an object using a convex lens are ___.

1. 2
2. 5
3. 3
4. 4

Q. For a concave lens, if the magnification has a plus sign, then image is _________ .

1. real and erect
2. real and inverted
3. virtual and erect
4. virtual and inverted

Q. Distance of an actual object is always as per cartesian sign convention.

1. positive
2. negative
3. zero

Q. For a concave lens, if the magnification has a plus sign, then image is _________ .

1. real and inverted
2. virtual and erect
3. virtual and inverted
4. real and erect

Q. Which of the following is true about concave lenses?

1. Focal length is positive
2. Image distance can be positive or negative
3. Height of image can be positive or negative
4. Image distance is always negative

Q. Choose the correct option.

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

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

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

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