Question

Consider the following processes.
(i).Electrical Oscillations
(ii).Rapid deceleration of fast electrons
(iii).Atomic transition
Which of these are likely to produce visible light?
(iii) only
(ii) and (iii)
(i) and (iii)
(i), (ii) and (iii)

Answer 1

The knowledge of the electromagnetic spectrum has to be recollected and be found out the range of frequency and wavelength for visible light. Now, for each phenomenon mentioned in the question, try to figure out if the frequency or the wavelength produced by them lies in the range of visible light or not to get the answer.

Complete Step By Step answer:
An electrical oscillator is mainly comprised of an inductor and a capacitor and is also known as an LC oscillator. It is commonly used to generate radio waves. But, we have to find out if it can generate a frequency in the visible range.
The range of wavelengths of visible light lies between $380nm$ to $750nm$ and the range of frequency lies between $400THz$ to $790THz$.
Now the frequency of an electrical oscillator can be found out using the formula:
$\omega = \dfrac{1}{{\sqrt {LC} }}......(1)$
Where,
$\omega$ is the frequency.
$L$ is the inductance of the inductor.
$C$ is the capacitance of the capacitor.
So, we will put the value of frequency that lies in the visible range in equation (1) and find out the approximate value of the product of the inductance and the capacitance. It will help to know if it is practically possible to get visible light or not.
Let the frequency be $500THz$. We will put this value in equation (1) to get,
$500 \times {10^{12}} = \dfrac{1}{{\sqrt {LC} }}$
$\Rightarrow LC = \dfrac{1}{{{{\left( {500 \times {{10}^{12}}} \right)}^2}}}$
$\Rightarrow LC \approx 4 \times {10^{ - 30}}$
So, if we use the inductor and capacitor having a value in the range of the Femtounit, we can get the visible light.
The rapid deceleration of fast electrons will produce electromagnetic radiation. Electromagnetic radiation is produced by the rapid deceleration of fast electrons when it is deflected by an atomic nucleus. The radiation produced in this process is known as Bremsstrahlung.
The moving electrons lose their kinetic energy and the lost kinetic energy gets converted into radiation by emitting photons. The frequency of emission of photons lies in the visible range.
The isolated atoms can absorb packets of electromagnetic radiation having discrete energies and goes into the excited state. As the excited state is unstable, the atoms emit photons of discrete energies and go back to the ground state.The frequency of the emitted photons lies in the visible range.

Hence, option (D) is correct.

Note:
The radiations of different frequencies and wavelengths have different spectrums. For instance, the radio works in the frequency range of radio waves. X-rays that are used to find fractured bones have a very high range of frequency. Gamma rays are very harmful rays and are emitted by radioactive elements like uranium, thorium etc. It has the highest frequency and lowest wavelength in the electromagnetic spectrum.