Electrons of mass m with de-Broglie wavelength λ fall on the target in an X-ray tube. The cutoff wavelength (λ0) of the emitted X-ray is :

A linear aperture whose width is 0.02 cm is placed immediately in front of a lens of focal length 60 cm. The aperture is illuminated normally by a parallel beam of wavelength 5 × 10^–5 cm. The distance of the first dark band of the diffraction pattern from the centre of the screen is :

A person can see clearly object only when they lie between 50 cm and 400 cm from his eyes. In order to increase the maximum distance of distinct vision to infinity, the type and power of the correcting lens, the person has to use, will be :

From which one of the following is the percentage of reflected amount of radiation highest?

Consider the following statements :

1. Different plant species grow together.
2. Light cannot penetrate into the lower strata full of undergrowth.

Which of the following types of vegetation is characterized by the above?

Which one of the following is the mode of heat tansfer in which warm material is transported so as to displace a cooler material?