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Question
_______ is a combination of two convex lenses with small focal length.
Options
simple microscope
compound microscope
telescope
none of these
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Solution
Compound microscope is a combination of two convex lenses with small focal length.
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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.
To find the image-distance for varying object-distances in case of a convex lens, a student obtains on a screen a sharp image of a bright object placed very far from the lens. After that he gradually moves the object towards the lens and each time focuses its image of the screen.
(a) In which direction – towards or away from the lens, does he move the screen to focus the object?
(b) What happens to the size of image – does it increase or decrease?
(c) What happen when he moves the object very close to the lens?
Complete the following table:
| Instrument | Number of Convex Lenses |
Use |
| Simple Microscope | .............. | .............. |
| Compound Microscope | .............. | .............. |
| Telescope | .............. | .............. |
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?
A convex lens has a focal length of 10 cm. At which of the following position should an object be placed so that this convex lens may act as a magnifying glass?
(a) 15 cm
(b) 7 cm
(c) 20 cm
(d) 25 cm
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.
Which part causes the greatest convergence?
The given below figure shows an object OA and its image IB formed by a lens.
The given below figure shows an object OA and its image IB formed by a lens. State three characteristics of the image.
A lens forms an upright and magnified image of an object State whether the image is real or virtual
In the following cases, where must an object be placed in front of a convex lens so that the image formed is inverted and enlarged?
Complete the following table:
| Type of lens | Position of object | Nature of image | Size of image |
| Convex | Between optical centre and focus | ||
| Convex | At focus | ||
| Concave | At infinity | ||
| Concave | At any distance |
While determining the focal length of a convex lens, you try to focus the image of a distant object formed by the lens on the screen. The image formed on the screen, as compared to the object, should be
(A) erect and highly diminished
(B) erect and enlarged
(C) inverted and enlarged
(D) inverted and highly diminished
For finding the focal length of a convex lens by obtaining the image of a distant object, one should use as the object.
(1) a well lit distant tree
(2) window grill in the class room
(3) any distant tree
(4) a lighted candle kept at the other end of the table.
Distinguish between:
Concave lens and Convex lens
A convex lens forms an inverted image of size same as that of the object which is placed at a distance 60 cm in front of the lens. Find: The position of image
Point out the difference between a convex lens and a concave lens.
Distinguish between:
Concave lens and Convex Lens
