An Observer Looks At A Tree Of Height 15 Metres With A Telescope Of Magnifying Power 10. To Him The Tree Appears:  

In a terrestrial telescope the focal length of erecting lens is 2 cm. The length of the telescope is 96 cm. If the magnifying power of the telescope is 10, then the focal lengths of eye-piece and objective are respectively:

The diameter of the moon is 3.5 × 10³ km and its distance from the earth is  seen by a telescope, having the focal lengths of the objective and the eye-piece as 4m and 10 cm respectively; the diameter of the image of the moon will be approximately:

The aperture of the largest telescope in the world is 5 m. if the separation between the moon and earth is 4 × 10⁵ km and the wavelength of visible light is 5000 Å, then the minimum separation between the objects on the surface of the moon which can be just resolved is approximately:  

The focal length of the objective lens of a telescope is 30 cm and that of its eye lens is 3 cm. It is focused on a scale 2 metres distant from it. The distance of the objective lens from the eye lens to see with relaxed eye is:

A good photographic print is obtained by an exposure of two seconds at a distance of 20 cm from the lamp. The time of exposure required to get an equally good result at a distance of 40 cm is: 

A camera objective has an aperture diameter d. If the aperture is reduced to diameter d/2, the exposure time under identical conditions of light should be made:   

A film projector magnifies a 100 cm² film strip on a screen. If the linear magnification is 4, the area of the magnified film on the screen is:

The resolution limit of the eye is 1 minute. At a distance x km from the eye, two persons stand with a lateral separation of 3 metre. For the two persons to be just resolved by the naked eye, x should be:

The minimum light intensity that can be perceived by the eye is about 10^–10 watt per metre². The number of photons of wavelength  metre that must enter the pupil of area 10^–4 m² per sec for vision is approximately equal to:    

The distance between the eye lens and cross-wires in Ramsden’s eye-piece which has a field lens of focal length 1.2 cm is: