Advertisements
Advertisements
Question
Write scientific reason.
Adults need bifocal lens spectacle.
Solution
- The ability of the ciliary muscles near the eye lens to change the focal length of the lens decreases with age.
- As a result, sometimes adults suffer from both nearsightedness and farsightedness.
Therefore, adults need bifocal lens spectacle.
APPEARS IN
RELATED QUESTIONS
(a) Draw a ray diagram to show the formation of an image by a convex lens when an object is placed in front of the lens between its optical centre and principal focus.
(b) In the above ray diagram, mark the object distance (u) and the image distance (v) with their proper signs (+ve or –ve as per the new Cartesian sign convention) and state how these distances are related to the focal length (f) of the convex lens in this case.
(c) Find the power of a convex lens which forms a real and inverted image of magnification –1 of an object placed at a distance of 20 cm from its optical centre.
"A convex lens can form a magnified erect as well as magnified inverted image of an object placed in front of it." Draw ray diagram to justify this statement stating the position of the object with respect to the lens in each case.
A student has obtained a magnified image of a flame on a screen using a convex lens. To draw the corresponding ray diagram to show the image formation, which of the following two rays whose paths after refraction are shown, should he select ?
(A) I and II
(B) II and III
(C) III and IV
(D) I and III
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.
Complete the following table:
| Instrument | Number of Convex Lenses |
Use |
| Simple Microscope | .............. | .............. |
| Compound Microscope | .............. | .............. |
| Telescope | .............. | .............. |
Draw a labelled ray diagram to show how a ray of light is refracted when it passes:
from air into an optically denser medium.
f the image formed by a convex lens is of the same size as that of the object, what is the position of the image with respect to the lens?
Where should an object be placed in front of a convex lens so as to obtain its real, inverted and magnified image?
What is a lens?
Distinguish between a convex lens and concave lens. Which of the two is a converging lens : convex lens of concave lens?
Describe with the help of a ray-diagram, the formation of image of a finite object placed in front of convex lens between f and 2f. Give two characteristics of the image so formed.
You eye contains a convex lens. Why is it unwise to look at the sun?
State whether convex lens has a real focus or a virtual focus.
In order to obtain a real image twice the size of the object with a convex lens of focal length 15 cm, the object distance should be:
(a) more than 5 cm but less than 10 cm
(b) more than 10 cm but less than 15 cm
(c) more than 15 cm but less than 30 cm
(d) more than 30 cm but less than 60 cm
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.
A convex lens of focal length 15 cm produces a magnification of +4. The object is placed:
(a) at a distance of 15 cm
(b) between 15 cm and 30 cm
(c) at less than 15 cm
(d) beyond 30 cm
A student did an experiment with a convex lens. He put an object at different distances 25 cm, 30 cm, 40 cm, 60 cm and 120 cm from the lens. In each case he measured the distance of the image from the lens. His results were 100 cm, 24 cm, 60 cm, 30 cm and 40 cm, respectively. Unfortunately his results are written in wrong order.
Rewrite the image distances in the correct order.
A student did an experiment with a convex lens. He put an object at different distances 25 cm, 30 cm, 40 cm, 60 cm and 120 cm from the lens. In each case he measured the distance of the image from the lens. His results were 100 cm, 24 cm, 60 cm, 30 cm and 40 cm, respectively. Unfortunately his results are written in wrong order.
What would be the image distance if the object distance was 90 cm?
The focal lengths of four convex lenses P, Q, R and S are 20 cm, 15 cm, 5 cm and 10 cm, respectively. The lens having greatest power is :
(a) P
(b) Q
(c) R
(d) S
Which part causes the greatest convergence?
The diagrams (a) and (b) in Figure below show the refraction of a monochromatic ray of light through a parallel sided glass block and a prism respectively. In each diagram, label the incident, refracted emergent rays and the angle of deviation.
Study the diagram given below.
- Name the lens LL’.
- What are the points O and O’ called?
- Complete the diagram to form the image of the object AB.
- State the three characteristics of the image.
- Name a device in which this action of lens is used.
A lens forms an erect, magnified, and virtual image of an object. Name the type of lens.
A lens forms an inverted image of an object. Name the kind of lens.
A convex lens has a divergent action and a concave lens has a convergent action.
A student focussed the image of a distant object using a device ‘X’ on a white screen ‘S’ as shown in the figure. If the distance of the screen from the device is 40 cm, select the correct statement about the device.
(A) The device X is a convex lens of focal length 20 cm.
(B) The device X is a concave mirror of focal length 40 cm.
(C) The device X is a convex mirror of radius of curvature 40 cm.
(D) The device X is a convex lens of focal length 40 cm.
Where should an object be placed in front of a convex lens to get a real image of the size of the object?
Answer the following question.
List four precautions which a student should observe while determining the focal length of a given convex lens by obtaining an image of a distant object on a screen.
How will you decide whether a given piece of glass is a concave lens, convex lens, or a plane glass plate?
State the position of object, position of image, nature of image when: Convex lens is used as objective lens of astronomical telescope.
A concave mirror and convex lens are held in water. What changes, if any, do you expect in their focal length?
Draw a diagram to show the convergent action of a convex lens by treating it as a combination of glass block and two triangular glass prisms, with the aid of two parallel incident rays.
Define the terms principal foci and focal lengths as applied to a convex lens, and show them with the help of proper diagrams.
Object at 2F1 of a convex lens : Image at 2F2 : : Object at F1 : _______
Simple microscope : Number of convex lens one : : compound microscope : _______
- In which type of microscope do you find the lens arrangement as shown in the following diagram?
- Write about the working and the use of this microscope.
Distinguish between Concave lens and Convex lens.
Distinguish between:
Concave lens and Convex Lens
Distinguish between Concave lens and Convex Lens.
