Electrostatic Potential and Capacitance — Physics STD 12 Science — Question

A freshly prepared radioactive sample of half- life 1 hour emits radiations that are 128 times as intense as the permissible safe limit. The minimum time after which this sample can be safely used is

(a) 14 hours

(b) 7 hours

(c) 128 hours

(d) 256 hours

In an hydrogen atom, the electron revolves around the nucleus in an orbit of radius 0.53 . Then the electrical potential produced by the nucleus at the position of the electron is

(a) – 13.6 V

(b) – 27.2 V

(c) 27.2 V

(d) 13.6 V

Light of wavelength  strikes a photo-sensitive surface and electrons are ejected with kinetic energy E. If  the kinetic energy is to be increased to 2E, the wavelength must be changed to   where

(a)

(b)

(c)  <

(d)

In terms of Rydberg's constant R, the wave number of the first Balmer line is

(a) R

(b) 3R

(c)

(d)

The rate of change of magnetic flux density through a circular coil of area 10m and number of turns 100 is 10³ Wb/ m²/ s. The value of induced emf will be.

For intensity I of a light of wavelength 5000Å the photoelectron saturation current is 0.40 μA and stopping potential is 1.36 V, the work function of metal is

(a) 2.47 eV

(b) 1.36 eV

(c) 1.10 eV

(d) 0.43 eV

Line spectra are due to

(a) Hot solids	(b) Atoms in gaseous state
(c) Molecules in gaseous state	(d) Liquid at low temperature

In Bohr’s model, if the atomic radius of the first orbit is  , then the radius of the fourth orbit is

(a)

(b) 4

(c)

(d) 16

The quantisation of charge indicates that: