© examsnet.com
Question : 12
Total: 12
CASE STUDY
A compound microscope consists of two converging lenses. One of them, of smaller aperture and smaller focal length is called objective and the other of slightly larger aperture and slightly larger focal length is called eye-piece. Both the lenses are fitted in a tube with an arrangement to vary the distance between them. A tiny object is placed in front of the objective at a distance slightly greater than its focal length. The objective produces the image of the object which acts as an object for the eye-piece. The eye piece, in turn produces the final magnified image.
1 × 5 = 5
I. In a compound microscope the images formed by the objective and the eye-piece are respectively.
(A) virtual, real
(B) real, virtual
(C) virtual, virtual
(D) real, real
II. The magnification due to a compound microscope does not depend upon
(A) the aperture of the objective and the eyepiece
(B) the focal length of the objective and the eye-piece
(C) the length of the tube
(D) the colour of the light used
III. Which of the following is not correct in the context of a compound microscope?
(A) Both the lenses are of short focal lengths.
(B) The magnifying power increases by decreasing the focal lengths of the two lenses.
(C) The distance between the two lenses is more thanleft ( f o + f e )
(D) The microscope can be used as a telescope by interchanging the two lenses.
IV. A compound microscope consists of an objective of10 mathrm X 20 X
(A) 2
(B) 10
(C) 30
(D) 200
V. The focal lengths of objective and eye-piece of a compound microscope are1.2 c m 3.0 c m 1.25 c m
(A) 100
(B) 150
(C) 200
(D) 250
A compound microscope consists of two converging lenses. One of them, of smaller aperture and smaller focal length is called objective and the other of slightly larger aperture and slightly larger focal length is called eye-piece. Both the lenses are fitted in a tube with an arrangement to vary the distance between them. A tiny object is placed in front of the objective at a distance slightly greater than its focal length. The objective produces the image of the object which acts as an object for the eye-piece. The eye piece, in turn produces the final magnified image.
I. In a compound microscope the images formed by the objective and the eye-piece are respectively.
(A) virtual, real
(B) real, virtual
(C) virtual, virtual
(D) real, real
II. The magnification due to a compound microscope does not depend upon
(A) the aperture of the objective and the eyepiece
(B) the focal length of the objective and the eye-piece
(C) the length of the tube
(D) the colour of the light used
III. Which of the following is not correct in the context of a compound microscope?
(A) Both the lenses are of short focal lengths.
(B) The magnifying power increases by decreasing the focal lengths of the two lenses.
(C) The distance between the two lenses is more than
(D) The microscope can be used as a telescope by interchanging the two lenses.
IV. A compound microscope consists of an objective of
(A) 2
(B) 10
(C) 30
(D) 200
V. The focal lengths of objective and eye-piece of a compound microscope are
(A) 100
(B) 150
(C) 200
(D) 250
Solution:
I. Option (B) is correct.
Explanation: Objective lens produces a real image which is positioned between the focus and the optical centre of eyepiece lens. So, eyepiece lens produces a virtual image.
II. Option (A) is correct.
Explanation: Magnification when image is formed at the near point of distinct vision is
( 1 +
)
No expression contains the aperture terms. So, magnification does not depend on aperture of the objective and the eyepiece.
III. Option (D) is correct.
Explanation: Both the lens of microscope are of short focal lengths and hence the microscope cannot be used as a telescope by interchanging the two lenses. Objective of telescope is of large focal length.
IV. Option (D) is correct.
Explanation:10 X 10 times 20 = 200
V. Option (C) is correct.
Explanation: Applying lens formula for objective lens,
−
=
Or,
+
=
∴ v 0 = 30 c m
magnification=
=
×
= 200
Explanation: Objective lens produces a real image which is positioned between the focus and the optical centre of eyepiece lens. So, eyepiece lens produces a virtual image.
II. Option (A) is correct.
Explanation: Magnification when image is formed at the near point of distinct vision is
No expression contains the aperture terms. So, magnification does not depend on aperture of the objective and the eyepiece.
III. Option (D) is correct.
Explanation: Both the lens of microscope are of short focal lengths and hence the microscope cannot be used as a telescope by interchanging the two lenses. Objective of telescope is of large focal length.
IV. Option (D) is correct.
Explanation:
V. Option (C) is correct.
Explanation: Applying lens formula for objective lens,
Or,
magnification
© examsnet.com
Go to Question: