The screen of a cathode ray tube cannot be coated with:
zinc sulphide
zinc platinocyanide
zinc silicate with manganese traces
barium platinocyanide
The rate of emission of electrons from a surface does not depend upon:
the temperature of surface
the shape of metal surface
the nature of the metal surface
the surface area of metal
The minimum amount of energy required to emit electrons from a metal surface is called the:
cohesive energy
work function
ionisation energy
dissociation energy
Why is the cathode ray tube evacuated to a low pressure?
To avoid the effect of external electric field on the beam of electrons.
To increase the energy of the beam of electrons.
To avoid collisions of electrons with the air molecules
To increase the rate of emission.
Which of the following is most harmful for the human being :
Light rays
Beta particles
Gamma rays
Alpha particles
Which of the following radiations suffers maximum deflection in magnetic field?
α - particles
β - particle
x - rays
γ - radiations
In β - emission from a radioactive substance an electron is ejected. This electron comes from
outer most orbit of atom
inner orbits of atom
the surface of substances
the nucleus of atom
The atoms of different elements which have same mass number A, but differ in their atomic number Z are called
Isotopes
Isobars
Isotones
Nucleons
Choose the work function of Platinum.
6.2
4.52
4.37
2.6
A radioactive substance is oxidised. What changes would you expect to take place in the nature of radioactivity ?
increases
decreases
remains constant
cannot be predicted
