Q. 03.7( 3 Votes )
A sphere of radius 1.00 cm is placed in the path of a parallel beam of light of large aperture. The intensity of the light is 0.50 W cm–2. If the sphere completely absorbs the radiation falling on it, find the force exerted by the light beam on the sphere.
If the is fully absorbing then force exerted is
Where I= intensity.
In this area, is the perpendicular area in which it falls.
Hence, force is
Rate this question :
Consider a 20 W bulb emitting light of wavelength and shining on a metal surface kept at a distance 2m. Assume that the metal surface has work function of 2 eV and that each atom on the metal surface can be treated as a circular disk of radius .
(i) Estimate no. of photons emitted by the bulb per second. [Assume no other losses]
(ii) Will there be photoelectric emission?
(iii) How much time would be required by the atomic disk to receive energy equal to work function (2 eV)?
(iv) How many photons would atomic disk receive within time duration calculated in (iii) above?
(v) Can you explain how photoelectric effect was observed instantaneously?
[Hint: Time calculated in part (iii) is from classical consideration and you may further take the target of surface area say 1cm2 and estimate what would happen?]
Physics - Exemplar
A neutron beam of energy E scatters from atoms on a surface with a spacing d = 0.1nm. The first maximum of intensity in the reflected beam occurs at θ = 30°. What is the kinetic energy E of the beam in eV?Physics - Exemplar
A particle A with a mass mA is moving with a velocity v and hits a particle B (mass mB) at rest (one dimensional motion). Find the change in the de Broglie wavelength of the particle A. Treat the collision as elastic.Physics - Exemplar
The de Broglie wavelength of a photon is twice the de Broglie wavelength of an electron. The speed of the electron is . ThenPhysics - Exemplar
Two particles A1 and A2 of masses m1, m2 (m1 > m2) have the same de Broglie wavelength. ThenPhysics - Exemplar
(i) In the explanation of photo electric effect, we assume one photon of frequency v collides with an electron and transfers its energy. This leads to the equation for the maximum energy Emax of the emitted electron as
where ϕ0 is the work function of the metal. If an electron absorbs 2 photons (each of frequency v) what will be the maximum energy for the emitted electron?
(ii) Why is this fact (two photon absorption) not taken into consideration in our discussion of the stopping potential?
Physics - Exemplar
A proton and an α-particle are accelerated, using the same potential difference. How are the de Broglie wavelengths λp and λa related to each other?Physics - Exemplar
Show that it is not possible for a photon to be completely absorbed by a free electronHC Verma - Concepts of Physics Part 2