P-1 Lenses Science - P-1 Lenses

The image obtained while finding the focal length of a convex lens is ……….. 

A student obtained a clear image of window grills on the screen. But the teacher told him to get the image of a tree far away, instead of the window. To get a clear image, the lens must be ………..

When an object is placed at any finite distance from a concave lens, the image is formed ………..

(1) Why do we have to bring a small object near the eyes in order to see it clearly?
(2) If we bring an object closer than 25 cm from the eyes, when can we not see it clearly even though it subtends a bigger angle at the eye?

From equations (1) and (2) what is the relation between h1, h2, u and v?

Planets, Stars, Satellites, Rainbow.

TV, Motion picture, Complete circle formed by a revolving burning incense stick, Colour blindness.

Compound microscope, Kaleidoscope, Simple microscope, Astronomical telescope.

We cannot clearly see an object kept at a distance less than 25 cm from the eye.

One can sense colours only in bright light.

A simple microscope is used for watch repairs.

It is risky to issue a driving license to a person suffering from colour-blindness.

Colour-blind persons are unable to distinguish between different colours.

If a convex lens of focal length 10 cm and a concave lens of focal length 50 cm are kept in contact with each other, (i) what will be the focal length of the combination? (ii) what wiil be the power of the combination? (iii) what will be the behaviour of the combination (behaviour as a convex lens/concave lens)?

Two convex lenses of equal focal lengths are kept in contact with each other. If the power of their combination is 20 D, find the focal length of each convex lens.

Two convex lenses of focal length 20 cm each are kept in contact with each other. Find the power of their combination.

The power of a convex lens is 2.5 dioptres. Find its focal length.
(OR)
Calculate the focal length of a corrective lens having power +2.5 D.

What is the power of a convex lens having focal length 0.5 m?

Concave lens and Convex lens.

Farsightedness (Hypermetropia) and Nearsightedness (Myopia).

At which position will you keep an object in front of a convex lens so as to get a real image of the same size as the object? Draw a figure.

A concave lens of focal length 12 cm and a convex lens of focal length 20 cm are kept in contact with each other, (i) Find the focal length of the combination, (ii) What will be the behaviour of the combination?

If a convex lens of focal length 20 cm and a concave lens of focal length 30 cm are kept in contact with each other, (i) What will be the focal length of the combination? (ii) What will be the power of the combination? (iii) What will be the behaviour of the combination?

Match the columns in the following table and explain them:

Column 1	Column 2	Column 3
Farsightedness	Nearby object can be seen clearly	Bifocal lens
Presbyopia	Faraway object can be seen clearly	Concave lens
Nearsightedness	Problem of old age	Convex lens

State the rules used for drawing ray diagrams for the formation of an image by a convex lens.

Construction of a compound microscope:
(1) A compound microscope consists of a metal tube fitted with two convex lenses at the two ends. These lenses are called the objective lens (the lens directed towards the object) and the eyepiece (the lens directed towards the eye). Both the lenses are small in size, but the cross section of the objective lens is less than that of the eyepiece. The objective lens has a short focal length. The focal length of the eyepiece is more than that of the objective lens.(2) The metal tube is mounted on a stand. The principal axes of the objective lens and the eyepiece are along the same line. The distance between the object and the objective lens can be changed with a screw. It is possible to change the distance between the objective lens and the eyepiece.
Working:
(1) The object to be observed is illuminated and placed in front of the objective lens, slightly beyond the focal length of the objective lens. Its real, inverted and enlarged image is formed by the, objective lens on the other side.
(2) This intermediate image lies within the focal length of the eyepiece. It serves as an object for the eyepiece. The eyepiece works as a simple microscope. The final image is virtual, highly enlarged and inverted with respect to the original object. It can be formed at the minimum distance of distinct vision from the eyepiece. The final image is observed by keeping the eye close to the eyepiece.
Use: This microscope is used to observe blood cells, microorganisms, etc.
1.In a compound microscope, which lens has greater focal length?
2.Where do you place the object to be observed with a compound microscope?
3.State which distance is adjusted to observe the object with a compound microscope.
4.State the nature of the final image in compound microscope relative to the object.
5.State the use of a compound microscope.

 An object kept 60 cm from a lens gives a virtual image 20 cm in front of the lens. What is the focal length of the lens? Is it a converging lens or diverging lens?

Three lenses having powers 2, 2.5 and 1.7 D are kept touching in a row. What is the total power of the lens combination?

Generally, using the same objective lens, but different eyepieces, different magnification can be obtained.

The conical cells respond to the intensity of light and communicate the degree of brightness and darkness to the brain.

The rod like cells respond to colours and communicate the presence of colours in the retinal image of the brain.

The conical cells can respond differently to red, green and blue colours.

In television, we see a continuous picture due to persistence of vision.

Name the instrument used to observe planets.

Name the instrument used to observe bacteria.

Name the lens for which the image always lies between the object and the lens.

Name the lens used to obtain the image on a screen.

Name the lens which always forms an image virtual and smaller than the object.