© examsnet.com
Question : 33
Total: 35
(a) (i) Draw a ray diagram to show the working of a compound microscope. Obtain the expression for the total magnification for the final image to be formed at the near point.
(ii) In a compound microscope an object is placed at a distance of1.5 cm 1.25 cm 5 cm
OR
(b) (i) Draw a ray diagram for the formation of image of an object by an astronomical telescope, in normal adjustment. Obtain the expression for its magnifying power.
(ii) The magnifying power of an astronomical telescope in normal adjustment is2 . 9 150 cm
(ii) In a compound microscope an object is placed at a distance of
OR
(b) (i) Draw a ray diagram for the formation of image of an object by an astronomical telescope, in normal adjustment. Obtain the expression for its magnifying power.
(ii) The magnifying power of an astronomical telescope in normal adjustment is
Solution: 👈: Video Solution
(a) (i) Ray diagram of compound microscope:
In a compound microscope there are two lenses - objective( O ) ( E )
ObjectP Q
An inverted, magnified, real imageP 1 Q 1 P 1 Q 1 P Q P 2 Q 2 D
Magnification:
For objective:
Object distance= u
Image distance= v
Magnification = m o =
=
Applying the lens formula,
−
=
Or,1 +
=
Or,
=
− 1
For eyepiece:
Magnification = m e = 1 +
Magnification of the combination of objective and eyepiece= m = m O × m e
Or, m =
× ( 1 +
)
Or, m = (
− 1 ) ( 1 +
)
P 1 Q 1 v
∴ m = (
− 1 ) ( 1 +
)
Since,f e ≪ D f 0 ≪ L
m =
×
(ii) Given,u = 1.5 cm , f 0 = 1.25 cm , f e = 5 cm , D = 25 cm
Here, all alphabets are in their usual meanings Applying lens formula for objective lens,
−
=
Or,
−
=
∴ v = 7.5 cm
Magnification= m =
× ( 1 +
)
Or, m =
× ( 1 +
)
∴ m = − 30
OR
(b) (i) Astronomical telescope in normal adjustment:
In an astronomical telescope there are two lenses - objective( O ) ( E )
The two lenses are so placed during focussing that the foci of the lenses meet at a point.
Objective is directed towards the object at infinity.
Parallel rays coming from the object meet at the focus of the objective and forms an inverted, real imageP 1 Q 1
This acts as the object of the eyepiece. An (inverted with respect toP 1 Q 1
Magnification= m
=
Or,m =
Or,m =
Or, m =
Or, m =
[α β tan α = α tan β = β
Or,m =
Or,m =
∴m =
(ii) Since, m =
Or, 2.9 =
∴ f o = 2.9 f e
Also, f o + f e = 150
Or, 2.9 f e + f e = 150
∴ f e =
= 38.46 cm
f O = 2.9 f c
= 2.9 × 38.46
= 111.54 cm
In a compound microscope there are two lenses - objective
Object
An inverted, magnified, real image
Magnification:
For objective:
Object distance
Image distance
Applying the lens formula,
Or,
Or,
For eyepiece:
Magnification of the combination of objective and eyepiece
Since,
(ii) Given,
Here, all alphabets are in their usual meanings Applying lens formula for objective lens,
Magnification
OR
(b) (i) Astronomical telescope in normal adjustment:
In an astronomical telescope there are two lenses - objective
The two lenses are so placed during focussing that the foci of the lenses meet at a point.
Objective is directed towards the object at infinity.
Parallel rays coming from the object meet at the focus of the objective and forms an inverted, real image
This acts as the object of the eyepiece. An (inverted with respect to
Magnification
Or,
Or,
[
Or,
Or,
∴
© examsnet.com
Go to Question: