class 12 modern physics dual nature of matter and nuclie and atoms
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Course
Physics
Institution
class 12 chapter s of modern physics feom ncert and cbse
chapter 11 dual nature of matter
chapter 12 atoms
chapter 13 nuclie
as per cbse and ncert from a well known platform physics wallah they are very short and cover all the concept in very short very helpfull for class12
Parishram 12thCBSE Board
FORMULA SHEET_DUAL NATURE OF RADIATION AND MATTER, ATOMS AND NUCLEI
The passage of electric current through air is called electric discharge through the air.
The voltage required for the discharge through air or gas depends upon (i) the nature of the gas, (ii) the pressure of the
gas, (iii) the nature of electrodes and (iv) distance between the electrodes.
Cathode rays are the stream of high speed electrons moving from cathode to anode in discharge tube at a pressure of
0.01 mm mercury.
Properties of cathode rays:
• Cathode rays travel in straight lines.
• Cathode rays produce heat in metals when they fall on them.
• Cathode rays are deflected by electric field and magnetic field.
• When fast moving cathode rays are stopped by a metal of high atomic number, Xrays are produced.
• Cathode rays can pass through thin aluminium or gold foils without puncturingthem.
Specific charge of cathode rays means charge/mass.
Specific charge was determined by J.J. Thomson, using electric and magnetic fields applied on a fine beam of electrons,
at same place but perpendicular to each other.
e E2
=
m 2VB 2
where E is the electric field applied, B is the magnetic field applied and V is the potential difference between anode and
cathode, under which the electron is accelerated before entering the electric and magnetic fields.
The value of specific charge of cathode ray (or electron) is 1.7589 × 1011 C kg–1
The charge of the electron as determined by Millikan, was found to be 1.602 × 10–19 C.
Millikan’s experiment proved that the minimum charge carried by all positive and negative ions is the same as the charge
on the electron.
The phenomenon of emission of electrons from metal surface by the action of light is called photoelectric effect and the
electrons so emitted are called photoelectrons.
According to quantum theory of radiation, radiation consists of tiny packets of energy called photons or light quanta.
Each photon has a definite amount of energy given by hυ, 2hυ, 3hυ, ... where h is Planck’s constant and υ is the
frequency of the radiation.
The rest mass of the photon is zero while the mass equivalent of moving photon is hυ/c2.
The minimum quantity of energy needed to remove an electron from metal surface is called work function.
Laws of photoelectric effect
(i) For a given photosensitive material and frequency of incident radiation (above the threshold frequency), the
photoelectric current is directly proportional to the intensity of light.
, 2
(ii) For a given photosensitive material and frequency of incident radiation, saturation current is found to be proportional
to the intensity of radiation whereas the stopping potential is independent of intensity.
(iii) For a given photosensitive material, there exists a certain minimum cutoff frequency, called the threshold frequency,
below which no emission of photoelectrons takes place, no matter how intense the light is. Threshold frequency is
different for different metals. Above the threshold frequency, the stopping potential or equivalently the maximum
kinetic energy of the emitted photoelectrons increases linearly with the frequency of the incident radiation, but is
independent of its intensity.
(iv) The maximum kinetic energy of the photoelectrons or stopping potential varies linearly with the frequency of
incident radiation, but is independent of its intensity.
(v) The photoelectric emission is an instantaneous process.
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