Radii of curvature of a converging lens are in the ratio 1 : 2. Its focal length is 6 cm and refractive mdex is 1.5. Then its radii of curvature are respectively
9 cm and 18 cm
6 cm and 12 cm
3 cm and 6 cm
4.5 cm and 9 cm
Light emitted during the de excitation of electron from n = 3 to n = 2, when incident on a metal, photoelectrons are just emitted from that metal. In which of the following de excitations photoelectric effect is not possible ?
From n = 2 to n = 1
From n = 3 to n = 1
From n = 5 to n = 2
From n = 4 to n = 3
The additional energy that should be given to an electron to reduce its de-Broglie wavelength from 1 nm to 0.5 nm is
2 times the intial kinetic energy
3 times the initial kinetic energy
0.5 times the initial kinetic energy
4 times the initial kinetic energy
The ionisation energy of an electron in the ground state of helium atom is 24.6 eV. The energy required to remove both the electron is
51.8 eV
79 eV
38.2 eV
49.2 eV
B.
79 eV
Ionisation energy in ground state = 24.6 eV
Energy required to remove 2n electron from He2+
= Z2 (13.6) eV =(2)2 (13.6) = 54.4 eV
So, total energy required = (24.6 + 54.4) eV
= 79 eV
Maximum velocity of the photoelectron emitted by a metal is 1.8 x 106 ms-1. Take the value of specific charge of the electron is 1.8 x 1011 C kg-1. Then the stopping potential in volt is
1
3
9
6
λ1 and λ2 are used to illuminate the slits. β1 and β2 are the corresponding fringe widths. The wavelength λ1 can produce photoelectric effect when incident on a metal. But the wavelength λ2 cannot produce photoelectric effect. The correct relation between β1 and β2 is
β1 < β2
β1 = β2
β1 > β2
β1 ≥ β2
Pick out the correct statements from the following
I, II are correct
I, III are correct
Only I is correct
II, III are correct
A radioactive substance emits 100 beta particles in the first 2 s and 50 beta particles 1n the next 2 s. The mean life of the smaple is
4 s
2 s
2 × 0.693 s
In which of the following statements, the obtained impure semiconductor is of p-type ?
Germanum is doped with bismuth
Silicon is doped with antimony
Germanium is doped with gallium
Silicon is doped with phosphorus