Video Lecture
Theory For Notes Making
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Objective Assignment
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Subjective Assignment
Q.1
How are X-rays produced ?
Q.2
How are microwaves produced ?
Q.3
Find the
(a) maximum frequency, and
(b) minimum wavelength of X-rays produced by 30 kV electrons.
Q.4
(i) Monochromatic light of frequency \displaystyle 6.0\times {{10}^{{14}}}Hz is produced by a laser. The power emitted is \displaystyle 2.0\,\times \,{{10}^{{-3}}}W. Estimate the number of photons emitted per second on an average by the source.
Q.5
X-rays fall on a photosensitive surface to cause photoelectric emission. Assuming that the work function of the surface can be neglected, find the relation between the de-Broglie wavelength ( \displaystyle \lambda ) of the electrons emitted to the energy \displaystyle \left( {{{E}_{v}}} \right) of the incident photons. Draw the nature of the graph of \displaystyle \lambda as a function of \displaystyle {{E}_{v}}.
Q.6
The energy flux of sunlight reaching the surface of the earth is 1.388 × 103 W/m2. How many photons (nearly) per square metre are incident on the Earth per second? Assume that the photons in the sunlight have an average wavelength of 550 nm.
Q.7
(a) An X-ray tube produces a continuous spectrum of radiation with its short wavelength end at 0.45 Å. What is the maximum energy of a photon in the radiation?
(b) From your answer to (a), guess what order of accelerating voltage (for electrons) is required in such a tube?
Q.8
In an accelerator experiment on high-energy collisions of electrons with positrons, a certain event is interpreted as annihilation of an electron-positron pair of total energy 10.2 BeV into two \displaystyle \gamma -rays of equal energy. What is the wavelength associated with each \displaystyle \gamma -ray? (1BeV = 109 eV)
Q.9
Crystal diffraction experiments can be performed using X-rays, or electrons accelerated through appropriate voltage. Which probe has greater energy? (For quantitative comparison, take the wavelength of the probe equal to 1 Å, which is of the order of inter-atomic spacing in the lattice) (me=9.11 × 10–31 kg).
Q.10
A lamp mainly emits light of wavelength \displaystyle \lambda . The lamp is rated at P watt and 8% of the energy is emitted as visible light.
(i) How many photons of light are emitted by the lamp per second?
(ii) How many photons are falling per second on a square whose length of each side is a, held perpendicular to the incident photons at a distance r from the lamp.
Q.11
X-rays of wave length \displaystyle \lambda fall on photosensitive surface, emitting electrons. Assuming that the work function of the surface can be neglected, prove that the de-Broglie wave length of electrons emitted will be \displaystyle \sqrt{{\frac{{h\lambda }}{{2\,mc}}}}.
Q.12
X-rays fall on a photosensitive surface to cause photoelectric emission. Assuming that the work function of the surface can be neglected, find the relation between the de-Broglie wavelength ( \displaystyle \lambda ) of the electrons emitted to the energy ( \displaystyle {{E}_{v}}) of the incident photons. Draw the nature of the graph for \displaystyle \lambda as a function of \displaystyle {{E}_{v}}.