Advertisements
Advertisements
प्रश्न
The total magnification produced by a compound microscope is 20. The magnification produced by the eye piece is 5. The microscope is focussed on a certain object. The distance between the objective and eyepiece is observed to be 14 cm. If least distance of distinct vision is 20 cm, calculate the focal length of the objective and the eye piece.
Advertisements
उत्तर
For the least distance of clear vision, the total magnification is given by:
`m=-L/`
where, L is the separation between the eyepiece and the objective
fo is the focal length of the objective
fe is the focal length of the eyepiece
D is the least distance for clear vision
Also, the given magnification for the eyepiece:
`m_e=5=(1+D/f_e)`
`=>5=1+20/f_e`
⇒fe= 5 cm
Substituting the value of m and me in equation (1), we get:
m=mo.me
`=>m_o=m/m_e=20/5=4`
Now, we have:
`m_0=L/(|f_0|)`
`=>f_0=14/4=3.5 "cm"`
APPEARS IN
संबंधित प्रश्न
A compound microscope consists of an objective lens of focal length 2.0 cm and an eyepiece of focal length 6.25 cm separated by a distance of 15 cm. How far from the objective should an object be placed in order to obtain the final image at
- the least distance of distinct vision (25 cm), and
- infinity?
What is the magnifying power of the microscope in each case?
A compound microscope uses an objective lens of focal length 4 cm and eyepiece lens of focal length 10 cm. An object is placed at 6 cm from the objective lens. Calculate the magnifying power of the compound microscope. Also calculate the length of the microscope.
Draw the labelled ray diagram for the formation of image by a compound microscope.
Derive the expression for the total magnification of a compound microscope. Explain why both the objective and the eyepiece of a compound microscope must have short focal lengths.
A compound microscope forms an inverted image of an object. In which of the following cases it it likely to create difficulties?
Can the image formed by a simple microscope be projected on a screen without using any additional lens or mirror?
A simple microscope using a single lens often shows coloured image of a white source. Why?
The magnifying power of a converging lens used as a simple microscope is `(1+D/f).` A compound microscope is a combination of two such converging lenses. Why don't we have magnifying power `(1+D/f_0)(1+D/f_0)`?In other words, why can the objective not be treated as a simple microscope but the eyepiece can?
A convex lens of a focal length 5 cm is used as a simple microscope. Where should an object be placed so that the image formed by it lies at the least distance of distinct vision (D = 25 cm)?
Draw a labelled ray diagram showing the formation of image by a compound microscope in normal adjustment. Derive the expression for its magnifying power.
With the help of a ray diagram, show how a compound microscope forms a magnified image of a tiny object, at least distance of distinct vision. Hence derive an expression for the magnification produced by it.
