Summary, Concept Map

SUMMARY

• Particle is a material object which is considered as a tiny concentration of matter (localized in space and time) whereas wave is a broad distribution of energy (not localized in space and time).

• The liberation of electrons from any surface of a substance is called electron emission.

• The minimum energy needed for an electron to escape from the metal surface is called work function of that metal.

• 1 eV is equal to 1.602 × 10^–19 J.

• The emission of electrons by supplying thermal energy is known as thermionic emission.

• Electric field emission occurs when a very strong electric field is applied across the metal.

• The emission of electrons due to irradiation of light is called photoelectric emission.

• Secondaryemissionistheprocessinwhichelectronsareemittedduetothebombardment of fast moving electrons.

• The photoelectric current (i.e. the number of electrons emitted per second) is directly proportional to the intensity of the incident light.

• Stopping potential is that the value of the negative (retarding) potential given to the collecting electrode A which is just sufficient to stop the most energetic photoelectrons emitted and make the photocurrent zero.

• The stopping potential is independent of intensity of the incident light.

• Maximum kinetic energy of the photoelectrons is independent of intensity of the incident light.

• For a given surface, the emission of photoelectrons takes place only if the frequency of incident light is greater than a certain minimum frequency called the threshold frequency.

• According to Planck, a matter is composed of a large number of oscillating particles (atoms) which vibrate with different frequencies.

• According to Einstein, the energy in light is not spread out over wavefronts but is concentrated in small packets or energy quanta.

• The individual light quantum of definite energy and momentum can be associated with a particle. This particle is named photon.

• Light behaves as a wave during its propagation and behaves as a particle during its interaction with matter.

• Photo electric cell or photo cell is a device which converts light energy into electrical energy.

• According to de Broglie hypothesis, all matter particles like electrons, protons, neutrons in motion are associated with waves. These waves are called de Broglie waves or matter waves.

• Wave nature of the electron is used in the construction of microscope called electron microscope.

• De Broglie hypothesis of matter waves was experimentally confirmed by Clinton Davisson and Lester Germer in 1927.

• Whenever fast moving electrons fall on the materials, a highly penetrating radiation, x-rays, is emitted.

• Continuous x-ray spectrum consists of radiations of all possible wavelengths with a certain minimum wavelength λ₀ .

• Characteristic x-ray spectra show some narrow peaks at some well – defined wavelengths when the target is hit by fast electrons.

CONCEPT MAP