Electromagnetic radiation - Practice Questions & MCQ

EM radiation -

According to electromagnetic wave theory, energy is emitted continuously from a source in the form of radiations (or waves), known as electromagnetic radiation. Electromagnetic radiations have both magnetic field as well as electric field components which oscillate in the phase perpendicular to each other as well as perpendicular to the direction of wave propagation. These waves do not require any medium for propagation and can propagate through vacuum. There are many types of electromagnetic radiations which constitute what is known as electromagnetic spectrum.

There are several parameters required to characterise or define a wave. These parameters are defined below:

                     1. Wavelength ($\lambda$): It is the distance travellled by the wave during one complete oscillation.

The maxima are called as Crests and the minima are called as Troughs. Alternatively, the distance between two consecutive crests or two consecutive troughs is also called as the wavelength.

        2. Time Period (T): It is the time required for one complete oscillation or one complete cycle by a wave.

        3. Frequency ($\nu$): It is number of waves produced by the source in one second

It is the inverse of the time period. Its SI unit is Hertz (Hz).

            $\nu=\frac{1}{\mathrm{~T}}$

        4. Speed (c): It is the distance travelled by the wave in one second.

            In one time period, the wave travels a distance equal to its wavelength.

$\mathrm{c}=\frac{\text { distance }}{\text { time }}=\frac{\text { Wavelength }}{\text { Time Period }}=\frac{\lambda}{\mathrm{T}}$

  $\because \nu=\frac{1}{\mathrm{~T}}$

$\therefore c=\nu \times \lambda$

The speed of all the different components of light is the same i.e. they travel with the speed of 3 $\times$ 10⁸ m/s. Their frequency and wavelength are different

5. Wave number ($\bar{\nu}$) : It is the inverse of the wavelength. It can also be defined as the number of wavelengths present in unit length.

                        $\bar{\nu}=\frac{1}{\lambda}$

• List of wavelengths for the electromagnetic spectrum

The rays present on the left extreme of the spectrum have the greatest frequency, least wavelegth and the greatest energy,

As the frequency increases, wavelength decreases and energy increases.