Important Terms Related to Spherical Lenses

Q.

Define the term focal length of a lens.

Q.

Name two factors on which the focal length of a lens depends.

Q.

Define the term principal axis of a lens.

Q. A student focused the image of a candle flame placed at 2 m from a convex lens of focal length 10cm, on a screen. After that he moves gradually the flame towards the lens and each time focuses its image on the screen

(A) In what direction does he move the lens to focus the flame on the screen?
(B) What happens to the size of the image of the flame formed on the screen?
(C) What difference is seen in the intensity (brightness) of the image of the flame on the screen?
(D) What is seen on the screen when the flame is very close (at about 5cm) to the lens?

Q.

Which lens has a virtual focus?

Q. focal length of a magnifying glass is 12.5cm. ratio of maximum and minimum magnifying power is 1)2:3 2)1:3 3)3:1 4)3:2

Q.

Study the diagram below.

(i) Name the lens LL'.

(ii) What are the points O and O' called ?

(iii) Complete the diagram to form the image of the object AB.

(iv) State three characteristics of the image.

Q.

Where is the image always formed by a concave lens?

Q.

What do you mean by focal plane of a lens?

Q. What happens when a ray of light gets refracted through a CONCAVE lense passing through F1?

Q. The line joining the centre of curvature and the pole of a spherical mirror is known as the principal axis.

1. True
2. False

Q. Complete the diagram given below to form the image of the object AB.

(a) Name the lens LL'.
(b) State the characteristics of the image.
(c) Name a device in which this action of the lens is used.
[5 MARKS]

Q.

Explain optical centre of a lens with the help of proper diagram(s).

Q. Mention the kind of lens that can form 1) virutal, errect and magnified image 2)real, inverted and diminished image 3) virutal, errect and diminished image.

Q.

It was observed that when the distance between an object and a lens decreases, the size of the image increases. What is the nature of this lens? If you keep on decreasing the distance between the object and the lens, will you still be able to obtain the image on the screen? Explain.

Q. A magnifying glass uses a convex lens because the image formed is _____.

1. diminished
2. enlarged
3. erect
4. virtual
5. real
6. inverted
7. closer to lens
8. visible to eye

Q.

Answer in brief:

Centre of curvature

Q.

Define centre of curvature.

Q. What is principal focus for concave lens?

1. None
2. It is a point on the principal axis of a concave lens from which a parallel beam of light rays, travelling parallel to the principal axis, appears to come after passing through the lens.
3. It is a point on the principal axis of a concave lens from which a perpendicular beam of light rays, travelling perpendicular to the principal axis, appears to come after passing through the lens.
4. It is a point on the principal axis of a convex lens at which a parallel beam of light rays, travelling parallel to principal axis, meet after passing through the lens.

Q. Define the principal focus of a convex lens and that of a concave lens.

Q.

Fill in the following blanks with suitable words : (a) Parallel rays of light are refracted by a convex lens to a point called the___ (b) The image in a convex lens depends upon the distance of the ___ from the lens.

Q. If a ray of light appears to meet on the focus of the concave lens on the same side as that of the source of light, then what is the correct path for the incident ray?

1. Incident ray is parallel to the principal axis.
2. Incident ray strikes the optical center of the lens.
3. Incident ray is passing through the focus on the same side as that of the source of light.

Q. The radius of curvature of a mirror is the radius of the sphere of which the mirror is a part.

1. True
2. False

Q.

A ray of light incident at a point on the principal axis of a convex lens passes undeviated through the lens. (a) What special name is given to this point on the principal axis ? (b) Draw a labelled diagram to support answer in part (a).

Q.

What kind of image do we see while watching a movie in a cinema hall?

1. Virtual

2. Complex

3. Real

4. Dynamic

Q. Define principal focus of the convex lens.

Q. Focal length of a lens made of glass does not depend on_______.

1. refractive index of surrounding
2. intensity of incident rays
3. radius of curvature of the surfaces
4. refractive index of the glass

Q. Define focal length of a lens.

Q.

Define Centre of curvature.

Q. Define focal length of a spherical lens.