Advertisements
Advertisements
प्रश्न
An equiconvex lens of focal length 'f' is cut into two identical plane convex lenses. How will the power of each part be related to the focal length of the original lens ?
Advertisements
उत्तर
\[\text{The focal length of original equiconvex lens is f } . \]
\[\text { Let the focal length of each part after cutting be F } . \]
\[\text { Here }, \]
\[\frac{1}{f} = \frac{1}{F} + \frac{1}{F}\]
\[ \Rightarrow \frac{1}{f} = \frac{2}{F}\]
\[ \Rightarrow f = \frac{F}{2}\]
\[ \Rightarrow F = 2f\]
\[\text { Power of each part will be given by }\]
\[P = \frac{1}{F}\]
\[ \Rightarrow P = \frac{1}{2f}\]
APPEARS IN
संबंधित प्रश्न
A beam of light converges at a point P. Now a lens is placed in the path of the convergent beam 12 cm from P. At what point does the beam converge if the lens is
- a convex lens of focal length 20 cm, and
- a concave lens of focal length 16 cm?
An object of size 3.0 cm is placed 14 cm in front of a concave lens of focal length 21 cm. Describe the image produced by the lens. What happens if the object is moved further away from the lens?
The image of a small electric bulb fixed on the wall of a room is to be obtained on the opposite wall 3 m away by means of a large convex lens. What is the maximum possible focal length of the lens required for the purpose?
A card sheet divided into squares each of size 1 mm2 is being viewed at a distance of 9 cm through a magnifying glass (a converging lens of focal length 9 cm) held close to the eye.
- What is the magnification produced by the lens? How much is the area of each square in the virtual image?
- What is the angular magnification (magnifying power) of the lens?
- Is the magnification in (a) equal to the magnifying power in (b)? Explain.
Two converging lenses of unequal focal lengths can be used to reduce the aperture of a parallel beam of light without loosing the energy of the light. This increase the intensity. Describe how the converging lenses should be placed to do this.
A convex lens forms a real image of a point object placed on its principals axis. If the upper half of the lens is painted black,
(a) the image will be shifted downward
(b) the image will be shifted upward
(c) the image will not be shifted
(d) the intensity of the image will decrease.
A pin of length 2.0 cm lies along the principal axis of a converging lens, the centre being at a distance of 11 cm from the lens. The focal length of the lens is 6 cm. Find the size of the image.
Will the focal length of a lens for red light be more, same or less than that for blue light?
In many experimental set-ups the source and screen are fixed at a distance say D and the lens is movable. Show that there are two positions for the lens for which an image is formed on the screen. Find the distance between these points and the ratio of the image sizes for these two points.
Show that the least possible distance between an object and its real image in a convex lens is 4f, where f is the focal length of the lens.
