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प्रश्न
When sunlight is concentrated on a piece of paper by a spherical mirror or lens, then a hole can be burnt in it. For doing this, the paper must be placed at he focus of:
(a) either a convex mirror or convex lens
(b) either a concave mirror or concave lens
(c) either a concave mirror or convex lens
(d) either a convex mirror or concave lens
उत्तर
either a concave mirror or a convex lens
Both a concave mirror and a convex lens focus parallel light beams coming from a distant object onto the focus.
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संबंधित प्रश्न
Due to gradual weakening of ciliary muscles and diminishing flexibility of the eye lens a certain defect of vision arises. Write the name of this defect. Name the type of lens required by such persons to improve the vision. Explain the structure and function of such a lens.
Where must the object be placed for the image formed by a converging lens to be:
virtual, upright and larger than the object?
State whether concave lens has a real focus or a virtual focus.
An object 2 cm tall stands on the principal axis of a converging lens of focal length 8 cm. Find the position, nature and size of the image formed if the object is:
(i) 12 cm from the lens
(ii) 6 cm from the lens
State one practical application each of the use of such a lens with the object in position (i) and (ii).
A beam of light is incident through the holes on one side of a box and emerges out through the holes on its opposite side as shown in the following figure:
The box contains:
(a) a glass prism
(b) a concave lens
(c) a convex lens
(d) a parallel-sided glass slab
State whether the following statement is true or false:
Short-sightedness can be cured by using a concave lens.
Study the diagram 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 three characteristics of the image.
An object of height 4 cm is kept at a distance of 30 cm from a concave lens. Use lens formula to determine the image distance, nature and size of the image formed if focal length of the lens is 15 cm.
An object is placed in front of a lens between its optical centre and focus. The formed image is virtual, erect, and diminished. Name the lens used.
A parallel, oblique beam of light falls on a concave lens. Draw a diagram to show refraction of light through the lens.
