Optical instruments - microscope and astronomical telescope — practice questions

Question 1 · difficulty L1 · recall

A simple microscope is essentially

• A. a converging lens used with the object within its focal length
• B. a diverging lens with object beyond 2f
• C. two plane mirrors only
• D. a prism with no lens

Question 2 · difficulty L1 · understanding

An astronomical telescope in normal adjustment produces its final image

• A. on the objective lens
• B. at infinity
• C. at the near point only
• D. inside the objective glass

Question 3 · difficulty L2 · understanding

Some distant star is to be observed by some telescope of diameter of objective lens $a$, at an angular resolution of $3.0 \times 10^{-7}$ radian. If the wavelength of light from the star reaching the telescope is 500 nm , the minimum diameter of the objective lens of the telescope is $\_\_\_\_$ cm. (nearest interger)

Question 4 · difficulty L2 · understanding

In a microscope the objective is having focal length $f_o=2 \mathrm{~cm}$ and eye-piece is having focal length $f_e=4 \mathrm{~cm}$. The tube length is 32 cm . The magnification produced by this microscope for normal adjustment is $\_\_\_\_$ .

Question 5 · difficulty L2 · understanding

A telescope with objective diameter $R$ is used to observe a distant star emitting light of wavelength 500 nm , at a resolution of $5 \times 10^{-7}$ radian. The value of $R$ is $\_\_\_\_$ cm .

• A. 61
• B. 122
• C. 244
• D. 305

Question 6 · difficulty L2 · understanding

A photograph of a landscape is captured by a drone camera at a height of 18 km . The size of the camera film is $2 \mathrm{~cm} \times 2 \mathrm{~cm}$ and the area of the landscape photographed is $400 \mathrm{~km}^2$. The focal length of the lens in the drone camera is :

• A. 2.8 cm
• B. 0.9 cm
• C. 2.5 cm
• D. 1.8 cm

Question 7 · difficulty L2 · understanding

Identify the physical quantity that cannot be measured using spherometer :

• A. Radius of curvature of concave surface
• B. Specific rotation of liquids
• C. Thickness of thin plates
• D. Radius of curvature of convex surface

Question 8 · difficulty L2 · understanding

In a reflecting telescope, a secondary mirror is used to:

• A. make chromatic aberration zero
• B. remove spherical aberration
• C. reduce the problem of mechanical support
• D. move the eyepiece outside the telescopic tube

Question 9 · difficulty L2 · understanding

A scientist is observing a bacteria through a compound microscope. For better analysis and to improve its resolving power he should. (Select the best option)

• A. Decrease the focal length of the eye piece.
• B. Increase the wave length of the light
• C. Increase the refractive index of the medium between the object and objective lens
• D. Decrease the diameter of the objective lens

Question 10 · difficulty L2 · understanding

In normal adujstment, for a refracting telescope, the distance between objective and eye piece is $$30 \mathrm{~cm}$$. The focal length of the objective, when the angular magnification of the telescope is 2 , will be :

• A. 20 cm
• B. 30 cm
• C. 10 cm
• D. 15 cm