Electromagnetic Radiation
Wave Characteristics & EM Spectrum | Structure of Atom
1. Electromagnetic Wave Theory
Proposed by James Clerk Maxwell (1870). It states that energy is emitted from any source continuously in the form of radiation.
Key Point: The radiation consists of oscillating Electric and Magnetic fields produced by oscillating charged particles. These fields are perpendicular to each other and to the direction of propagation of the wave.
Unlike sound waves, EM waves do not require a medium and can travel through a vacuum.
2. Characteristics of EM Waves
A. Wavelength ($\lambda$)
The distance between two consecutive crests or troughs.
- Units: Meter ($m$), Angstrom ($1 \mathring{A} = 10^{-10} m$), Nanometer ($1 nm = 10^{-9} m$), Picometer ($1 pm = 10^{-12} m$).
B. Frequency ($\nu$)
The number of waves passing through a point in one second.
- Units: Hertz ($Hz$), $s^{-1}$, or cycles per second (cps).
C. Velocity ($c$)
All EM radiations travel with the speed of light in vacuum.
$$ c = 3 \times 10^8 \, m/s $$
D. Wave Number ($\bar{\nu}$)
The number of wavelengths per unit length. Reciprocal of wavelength.
$$ \bar{\nu} = \frac{1}{\lambda} \quad (\text{Unit: } m^{-1} \text{ or } cm^{-1}) $$
E. Relation between $\lambda, \nu, c$
$$ c = \nu \times \lambda \quad \Rightarrow \quad \nu = \frac{c}{\lambda} $$
3. The Electromagnetic Spectrum
Arrangement of EM radiations in order of increasing wavelength (or decreasing frequency/energy).
| Radiation | Trend |
|---|---|
| Cosmic Rays |
$\downarrow$ Wavelength Increases $\uparrow$ Frequency Increases $\uparrow$ Energy Increases |
| Gamma Rays ($\gamma$) | |
| X-Rays | |
| Ultraviolet (UV) | |
| Visible (VIBGYOR) | |
| Infrared (IR) | |
| Microwaves | |
| Radio Waves |
Visible Region: Violet (~400 nm) to Red (~750 nm).
Practice Quiz
Test your understanding of Wave Properties.
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