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प्रश्न
Express power of a concave lens of focal length 50 cm with its sign.
उत्तर
Power = `1/"focal length (in metres)"`
Now, a concave lens has a virtual focal length ; \ f = -50 cm
Power = `100/-50` = -2D
Powerof a concave lens is negative and the power is -2D.
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संबंधित प्रश्न
Explain with the help of a diagram, why the concave lens is also called a diverging lens.
A small bulb is placed at the focal point of a converging lens. When the bulb is switched on, the lens produces:
(a) a convergent beam of light
(b) a divergent beam of light
(c) a parallel beam of light
(d) a patch of coloured light
An illuminated object is placed at a distance of 20 cm from a converging lens of focal length 15 cm. The image obtained on the screen is:
(a) upright and magnified
(b) inverted and magnified
(c) inverted and diminished
(d) upright and diminished
If the image formed by a lens is always diminished and erect, what is the nature of the lens?
Which type of lenses are:
thinner in the middle than at the edges?
Fill in the following blank with suitable word:
Lenses refract light to form images: a..................... lens can form both real and virtual images, but a diverging lens forms only ...................... images.
An object lies at a distance of 2f from a concave lens of focal length f. Draw a ray-diagram to illustrate the image formation.
An object is placed at a distance of 4 cm from a concave lens of focal length 12 cm. Fine the position and nature of the image.
Distinguish between concave and convex lens.
A concave lens has a focal length 30 cm. Find the position and magnification (m) of the image for an object placed in front of it at distance 30 cm. State whether the image is real or virtual?
