Why is graphite coating made on the inner side of the cathode ray tube ?
To change the brightness pattern on screen
To avoid the effect of external electric field on the beam of electrons
To avoid collisions of electrons with the air molecules
To produce fluorescence on the screen
The material used for safety from nuclear radiations is
Lead
Platinum
Copper
Iron
Which of the following metals cannot be used to coat tungsten inorder to reduce its work function?
Magnesium
Strontium
Cesium
Barium
A certain nucleus X has a mass number 15 and atomic number 7.Find the number of neutrons.
15
7
8
22
Speed of beta particle is
107 m/s
2.7 x 108 m/s
3 x 108 m/s
108 m/s
Which substance is most suitable to be used as an electron emitter?
Na
Ni
W
K
The maximum number of electrons in a shell of number 'n' is given by.
2n
22n
2n2
n3
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
Which of the following is not a primary colour?
Red
Green
Yellow
Blue
Which of the following is most harmful for the human being :
Light rays
Beta particles
Gamma rays
Alpha particles
