Modern research and experiments proves that every moving object posses a wave associated with it's motion. Properties related to the wave become more intense when the object moving is very small.
Hence, the electrons revolving the nucleus must possess a very strong wave nature. It becomes very important to study the wave nature of sub atomic particles to fully understand the structure and stability of atom.
You already know that
- Light radiations have a dominant wave nature.
- Physically existing objects have a particle nature.
You will learn that
- Light also posses particles hence has particle nature too.
- Moving objects also have a wave associated with them hence the wave nature.
In this article, you will study about the dual nature of Matter and Radiation by studying various theories and studying different phenomenon. It will construct your strong understand about the wave properties of the subatomic particles. But, before you begin to study wave properties, it is important to make yourself familiar to what wave actually means.
Introduction to Electromagnetic Waves
- It is the energy transmitted from one body to another in the form of waves and these waves travel in the space with the same speed as light ( 3 × 108 m/s) and these waves are known as Electromagnetic waves or radiant energy.
- The radiant Energy do not need any medium for propagation.
Ex : Radio waves, micro waves, Infra red rays, visible rays, ultraviolet rays, x–rays, gamma rays and cosmic rays.
Electromagnetic Spectrum
It is a collection of several types of radiations arranged in an order of increasing frequency and decreasing wavelength.
Properties of a wave
1. Wavelength (λ, Lambda):
It is defined as the distance between two nearest crest or nearest trough. It is measured in terms of a A° (Angstrom), pm (Picometre), nm (nanometer), cm (centimeter),
m (meter).
2. Frequency (v, Nu): Frequency of a wave is defined as the number of waves which pass through a point in 1 sec. It is measured in terms of Hertz (Hz ), sec–1 , or cycle per second (cps)
3. Time period (T): Time taken by a wave to pass through one point. 1 T sec.
4. Velocity (c):Generally, velocity is represented by 'v', but velocity of anything moving with the speed of light is represented by 'c'. Velocity of a wave is defined as distance covered by a wave in 1 sec.
5. Wave number (á¹½, nu bar):It is the reciprocal of the wave length that is number of waves present
in 1 cm
ṽ = 1/λ
1/cm=100/m
1 cm-1 = 100 m-1
6. Amplitude (a): The amplitude of a wave is defined as the height of crust or depth of trough.
Wave Nature of Matter and Radiation
Maxwell's Theory
1. Maxwell suggested that when electrically charged particles move under acceleration, they produce alternating electric and magnetic fields.
2. These fields transmit in the form of waves called electromagnetic waves or electromagnetic radiation.
3. Electric and magnetic fields travels in perpendicular direction to each other as well as the direction of propagation of wave.
4. Therefore, Maxwell's theory suggested that electrons must also have a wave nature associated with them.
Plank's Quantum Theory
1. The radiant energy emitted or absorbed by a body not continuously but discontinuously in the form of small discrete packets of energy and these packets are called quantum.
2. In case of light, the smallest packet of energy is called as 'photon' but in general case the smallest packet of energy called as quantum.
3. The energy of each quantum is directly proportional to frequency of the radiation i.e.
h = Plank's constant = 6.626 x 10-37 kJ sec-1
v= frequency of the wave associated with it.
Proportionality constant or Plank's constant (h) h = 6.626 × 10–37 kJ sec. or 6.626 × 10–34 J sec
(1 erg = 10–7J) or 6.626 × 10–27 erg sec.
4. Total amount of energy transmitted from one body to another will be some integral multiple of energy of a quantum.
E = nhv
Where n is an integer and n = number of quantum
E = hv= hc/λ = hcṽ
Particle Nature of Matter and Radiation
Black Body Radiations
This phenomenon indicates that heated objects emit radiations with variable intensity.
- Hot objects emit radiations over a wide range of wavelengths.
- Heating a steel plate only on the tip creates such color pattern.
- It means that yellow radiation is prominent at a specific temperature and blue radiation is prominent at a specific temperature.
- An iron rod that is being heated shows different color at different temperatures.
Black body is an imaginary body which can absorb and emit the radiations of all frequencies. The radiation emitted by such body are called black body radiations.
The intensity of radiation of different wavelengths emitted by a hot body depend on it’s temperature. The intensity of light is a measure of number of particles being emitted. Therefore, there is some particle nature in the radiations emitted by the heated body as well.
Photoelectric Effect
It is the phenomenon of ejection of electrons from a metal sheet when light falls on it. This phenomenon also proves that light radiations also have a particle nature.
- H. Hertz performed an experiment in which he exposed metal surfaces to a beam of light. As a result, electrons got ejected from the surface of metal.
- The number of electrons ejected depend on the intensity of radiation.
- For every metal, there is a certain minimum frequency below which, the photoelectric effect is not observed.
- Kinetic energy of ejected electrons increase with increase in the frequency of radiation.
Energy of light = Energy required to eject electron + kinetic energy
Conclusions made from the Experiment:
- Light carry particles filled with quantized energy (energy packets) called quanta or photons. E can be 0, hv, 2hv, 3hv ... nhv.
- When these quanta strike the metal surface, they transfer their energy to the electrons, hence electrons escape from their orbits and come on the surface of metal.
- Ejection of electron will only happen if quanta carry sufficient threshold energy required by the electron to escape its orbit. hνquanta = hνthreshold + KE
- Energy of incident radiation can be lesser than, equal to or more than that of threshold energy.
i. Vi < Vo; Ejection of electron is not observed.
ii. Vi = Vo; Electrons are ejected but their KE is zero afterwards.
iii. Vi > Vo; Electrons move with a kinetic energy after they are ejected.
After reading this article, it must be clear to you that both, matter and radiation have dual nature, i.e. wave nature and particle nature. For any questions, queries or suggestions, leave your comments below.
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