Hydrogen atoms are excited from ground state of the principle quantum number 4. Then the number of spectral lines observed will be
3
6
5
2
The electronic configuration for the noble gas in
;
Heavy water is used as a moderator in a nuclear reactor. The function of the moderator is
To control energy released in the reactor
To absorb neutrons and stop chain reaction
To cool the reactor
To slow down the neutrons to thermal energies.
The mass number of He is 4 and that for sulphur is 32. The radius of sulphur nuclei is larger than that of helium by
2
4
Doubly ionized helium atoms and hydrogen ions are accelerated from rest through the same potential drop. The ratio of the final velocities of the helium and the hydrogen ion is
1/2
2
Gases begin to conduct electricity at low pressure because
At low pressures gases turn of plasma
Colliding electros can acquire higher kinetic energy due to increases mean fee path leading to ionisation of atoms
Atoms break up into electrons and protons
The electrons in atoms can move freely at low pressures
Which o the following theories is the most satisfactory about the origin of the universe ?
Big Bang theory
Pulsating theory
Steady state theory
None of above
The nature of ions knocked out from hot surface is
Protons
Electrons
Neutrons
Nuclei
The spectrum obtained from a sodium vapour lamp is an example of
Band spectrum
Continuous spectrum
Emission spectrum
Absorption spectrum
When a hydrogen atom is raised from the ground state to an excited sate,
P.E decreases and K.E. increases
P.E. increases and K.E. decreases
Both K.E. and P.E. decreases
Absorption spectrum
If the threshold wavelength for a certan metal is 2000 Å , then the work –function of the metal is
6.2 J
6.2 eV
6.2 MeV
6.2 keV
The mass number of He is 4 and that of sulphur is 32. The radius of sulphur nucleus is larger than that of helium by a factor o
8
4
2
What is the respective number of and particles emitted in the following radioactive decay ?
6 and 8
6 and 6
8 and 8
8 and 6
A nucleus ruptures into two nuclear parts, which have their velocity ratio equal to 2 : 1. What will be the ratio of their nuclear size (nuclear radius) ?
The wavel3enght associated with an electron, accelerated through a potential difference of 100 V, is of the order of
1000 Å
100 Å
10.5 Å
1.2 Å
An electron of mass m and charge e is accelerated from rest through a potential difference of V volt in vacuum. Its final speed will be
Which of the following statement is correct ?
Photocurrent increases with intensity of light
Photocurrent is proportional to the applied voltage
Current in photocell increases with increasing frequency
Stopping potential increases with increases of incident light
Cosmic rays are
Highly energy radiations
Low energy radiations
Ultra high energy radiations
Very low energy radiations
The X-rays can not be diffracted by means of an ordinary grating because of
High speed
Short wavelength
Large wavelength
None of these
When hydrogen atom is in its first excited level, its radius is
Four times its ground state radius
Twice
Same
Half
The stable nucleus that has a radius half that of is