Modern Physics ...

Which one of the following statements is WRONG in the context of X-rays generated from a X-ray tube?

A radioactive sample S₁ having an activity 5_µCi has twice the number of nuclei as another sample S₂ which has an activity of 10 _µCi. The half lives of S₁ and S₂ can be

Photoelectric effect experiments are performed using three different metal plates p, q and r having work functions φ_p = 2.0 eV, φ_q = 2.5 eV and φ_r = 3.0 eV, respectively. A light beam containing wavelengths of 550 nm, 450 nm and 350  nm with equal intensities illuminates each of the plates. The correct I-V graph for the experiment is  [Take hc = 1240 eV nm]

The wavelength of the first spectral line in the Balmer series of hydrogen atom is 6561 A°. The wavelength of the second spectral line in the Balmer series of singly-ionized helium atom is

A pulse of light of duration 100 ns is absorbed completely by a small object initially at rest. Power of the pulse is 30 mW and the speed of light is 3×10⁸ ms^–1. The final momentum of the object is

If λ_Cu is the wavelength of K_α X-ray line of copper (atomic number 29) and λ_Mo is the wavelength of the K_α X-ray line of molybdenum (atomic number 42), then the ratio λ_Cu/λ_Mo is close to

A metal surface is illuminat ed by light of two different wavelengths 248 nm and 310 nm. The maximum speeds of the photoelectrons corresponding to these wavelengths are u₁ and u₂, respectively. If the ratio u₁ : u₂ = 2 : 1 and h_c = 1240 eV nm, the work function of the metal is nearly

In a historical experiment to determine Planck's constant, a metal surface was irradiated with light of different wavelengths. The emitted photoelectron energies were measured by applying a stopping potential. The relevant data for the wavelength (λ) of incident light and the corresponding stopping potential (V₀) are given below :

Given that c = 3 × 10⁸m s^–1 and e = 1.6 × 10^–19 C , Planck's constant (in units of J s) found from such an experiment is

The electrostatic energy of Z protons uniformly distributed throughout a spherical nucleus of radius R is given by 

The measured masses of the neutron  are 1.008665 u, 1.007825 u, 15.000109 u and 15.003065 u, respectively. Given that the radii of both the  nuclei are same, 1 u = 931.5 Me V/c² (c is the speed of light) and e²/(4 πε₀) = 1.44 MeV fm. Assuming  that the difference between the binding energies of   is purely due to the electrostatic energy, the radius of either of the nuclei is (1 fm = 10^–15 m)

An accident in a nuclear labora tory resulted in deposition of a certain amount of radioactive material of half-life 18 days inside the laboratory. Tests revealed that the radiation was 64 times more than the permissible level required for safe operation of the laboratory. What is the minimum number of days after which  the laboratory can be considered safe for use?