Optical Instruments

To increase the angular magnification of a simple microscope, one should increase:

• the focal length of the lens

• the power of the lens

• the aperture of the lens

• the object size

An optical instrument used for magnification has power 25 D of objective and 20 D of eyepiece. Whether it is a microscope or a telescope?

• Microscope

• Telescope

The eyepiece of an astronomical telescope has a focal length of 10 cm. The telescope is focused for normal vision of distant objects when the tube length is 1 m. The focal length of the objective is:

• 20 cm

• 10 cm

• 90 cm

• 100 cm

If the focal length of the objective lens is increased then,

• Magnifying power of microscope will increase but that of telescope will decrease

• Magnifying power of microscope and telescope both will increase

• Magnifying power of microscope and telescope both will decrease

• Magnifying power of microscope will decrease but that of telescope will increase

The magnification produced by the objective lens and the eye lens of a compound microscope are 25 and 6 respectively. The magnifying power of this microscope is:

• 19

• 31

• 150

• 120

The objective of a compound microscope is essentially:

• A concave lens of small focal length and small aperture

• Convex lens of small focal length and large aperture

• Convex lens of large focal length and large aperture

• Convex lens of small focal length and small aperture

A compound microscope has two lenses. The magnifying power of one is 5 and the combined magnifying power is 100. The magnifying power of the other lens is:

• 10

• 20

• 50

• 25

We make the approximation that ...

• Light rays from the object are parallel at the telescope

• Light rays are coming from at least 1 parsec away

• Light rays are not affected by Earth's atmosphere

• Light rays will form a perfect image on our screen

For angular magnification we use the equation

•  $=\frac{f_e}{f_o}$  

•  $=\frac{f_o}{f_e}$  

•  $=\frac{2\alpha}{\beta}$  

•  $=\frac{2\beta}{\alpha}$  

A Cassegrain telescope uses how many mirrors and lenses

• 2 mirrors and 1 lens

• 3 mirrors and 1 lens

• 2 mirrors and 2 lenses

• 2 mirrors and no lenses