We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF or read online on Scribd
You are on page 1/ 4
( ,
_ Problems For Practice
1. What must be the focal length of a lens useq die
simple microscope of magnifying power 26 ? The
final image is formed at the distance of distinct
vision. (Ans. 1 cm)
2. Aconverging lens of power 100 dioptre is used as
simple microscope. What is its magnifying power,
if the distance of distinct vision is 25 cm ?
(Ans. 26)
3. A converging lens of focal length 6.25 cm is used as
a magnifying glass. If the near point of the observer
is 25 cm from the eye and the lens is held close to
the eye, calculate (i) the distance of the object from
the lens and (ii) the angular magnification. Find the
angular magnification when the final image is
formed at infinity. [Ans. (i) 5 cm (ii) 5, 4] 4, The focal lengths of the objective and eyepiece of a
microscope are 1.25 cm and 5cm respectively. Find
the position of the object relative to the objective in
order to obtain an angular magnification of 30 in
normal adjustment. [CBSE D 12; OD 20]
(Ans. — 1.46cm)
5. The focal lengths of the objective and the eyepiece
of a microscope are 2 cm and 5 cm respectively and
the distance between them is 20 cm. Find the
distance of the object from the objective when the
final image seen by the eye is 25 cm from the
eyepiece. Also find the magnifying power.
(Ans. 4 =- 2.30m, m= 41.5)
6. A compound microscope is made using a lens of
focal length 10 mm as objective and another lens of
focal length 15 mm as eyepiece. An object is held at
1,1 cm from the objective and final image is formed
at infinity. Calculate distance between objective
and eyepiece. (Ans. 12.5 cm) 7. As shown in Fig. 9.132, PQ is the ray incident on a
prism ABC. Show the corresponding refracted and
emergent rays. The critical angle for the material of
the prism is 45°. Also find the refractive index of the
material of the prism. (Ans. /2)
A
[\
® 90°
{~
B Cc
Fig. 9.132
8. A ray of light falls on a glass prism at an angle of
incidence of 30°. Find the direction of the emergent
ray if the angle of the prism is 60° and refractive
index is 1.50. (Ans. i! =77°7')
9. A thin prism of 6° angle gives.a deviation of 3°.
What is the refractive index of the material of the
prism ? (Ans. 1.5) 10. A telescope objective has a focal length of 100 cm.
When the final image is formed at the least distance
of distinct vision, the distance between the lenses is
105 cm. Calculate the focal length of the eyepiece
and the magnifying power of the telescope.
(Ans. 6.25 cm, 20)
. A refracting telescope has an objective of focal
length 1 m and an eyepiece of focal length 20 cm.
The final image of the sun 10 cm in diameter is
formed at a distance of 24 cm from the eyepiece.
What angle does the sun subtend at the objective ?
(Ans. 0.0455 rad)
A reflecting type telescope has a concave reflector
of radius of curvature 120 cm. Calculate focal
length of eyepiece to secure a magnification of 20.
(Ans. 3 cm)
