Related InterviewSolutions

• A microwave oven operates at `2.5` GHz. Assume that `5%` of microwave photons are absorbed by 200 ml of water kept inside the oven. The time needed to warm the water from `20^(@)C `to `70^(@)C` is 2 minute. Specific heat capacity of water is `4.2 Jg^(–1) .^(@)C^(–1)`. Neglect any heat loss by water to the surrounding. Calculate the number of photons emitted per second per kilowatt of power consumed by the microwave. Efficiency of the oven to convent electrical energy into microwave energy is `70%`
• When photons of wavelength `lambda_(1) = 2920 Å` strike the surface of metal A, the ejected photoelectron have maximum kinetic energy of `k_(1) eV` and the smallest de-Broglie wavelength of `lambda`. When photons of wavelength `lambda_(2) = 2640 Å` strike the surface of metal B the ejected photoelectrons have kinetic energy ranging from zero to `k_(2) = (k_(1) – 1.5) eV`. The smallest de-Broglie wavelength of electrons emitted from metal B is `2lambda`. Find (a) Work functions of metal A and B. (b) `k_(1)` Take `hc = 12410 eV Å`
• X-ray spectrum obtained from a metallic target has been shown in the figure. The spectrum has been obtained for four different accelerating voltages in the X-ray tube: `25 kV`, `20 kV`, `15 kV` and `10 kV`. (a) Find the value of `lambda_(0)` shown in the graph. (b) What can you say about the energy of a K-shell electron in the target atom?
• A `mu` – meson (charge `= – e`, mass`= 208 m_(e)`) moves in a circular orbit around a heavy nucleus having charge `+ 3e`. Find the quantum state n for which the radius of the orbit is same as that of first Bohr orbit for hydrogen atom.
• In photoelectric experiment set up, the maximum kinetic energy `(k_("max"))` of emitted photoelectrons was measured for different wavelength `(lambda)` of light used. The graph of `k_("max")` vs `1/(lambda)`   ​ was obtained as shown in first figure. In the same setup, keeping the wavelength of incident light fixed at l, the applied potential difference was varied and the photoelectric current was recorded. The result has been shown in graph in second figure. (a) Find `lambda` is `Å` (b) Taking the photo efficiency to be `2%` (i.e. percentage of incident photons which produce photoelectrons) find the power of light incident on the emitter plate in the experiment. [Take `hc = 12400 eV Å`]
• A point source is emitting 0.2 W of ultravio- let radiation at a wavelength of `lambda = 2537 Å`. This source is placed at a distance of `1.0 m` from the cathode of a photoelectric cell. The cathode is made of potassium (Work function `= 2.22 eV`) and has a surface area of `4 cm^(2)`. (a) According to classical theory, what time of exposure to the radiation shall be required for a potassium atom to accumulate sufficient energy to eject a photoelectron. Assume that radius of each potassium atom is 2 Å and it absorbs all energy incident on it. (b) Photon flux is defined as number of light photons reaching the cathode in unit time. Calculate the photon flux. (c) Photo efficiency is defined as probability of a photon being successful in knocking out an electron from the metal surface. Calculate the saturation photocurrent in the cell assuming a photo efficiency of 0.1. (d) Find the cut – off potential difference for the cell.
• Find the change in energy of a photon of blue light `(lambda = 400 Å)` when the light enters into a medium of refractive index `mu = 4/3`.
• A square plate of side length L absorbs all radiation incident on it. A point source of light is placed at a point P which is directly above a corner of the plate at a height L. The incident light on the plate produces a force of magnitude `F_(0)` on the plate. Calculate the magnitude of force on the plate if the source is moved to a point Q (Q is midpoint of the line PR).
• Absorption spectrum is obtained for a sample of gas having atomic hydrogen in ground state. Which lines of the spectrum will be in the range `94 nm` to `122 nm`. Take Rydberg’s constant `R = 1.1 × 107 m^(–1)`
• In a hypothetical hydrogen-like atom the wavelength in A° for the spectral lines for transitions from `n = P` to `n = 1` are given by `lambda = (1500 p^(2))/(p^(2) - 1)` where `p` is an integer larger than is the ionization potential of this atom ?