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Physics · 2022 · 3 marks
CBSE 2022 · Region 3 · Set 1 · Q11
(a) Electromagnetic waves of wavelengths λ_1, λ_2 and λ_3 are used in radar systems, in water purifiers and in remote switches of TV, respectively.…
(a)
Electromagnetic waves of wavelengths $\displaystyle \lambda_{1}, \lambda_{2}$ and $\displaystyle \lambda_{3}$ are used in radar systems, in water purifiers and in remote switches of TV, respectively.
(i)
Identify the electromagnetic waves, and
(ii)
Write one source of each of them.
OR
(b)(i)
State two conditions for two light sources to be coherent.
(ii)
Give two points of difference between an interference pattern due to a double - slit and a diffraction pattern due to a single slit.
Marking-scheme solution
a)
| EM Waves | Sources |
| $\displaystyle \lambda_{1} \rightarrow$ Microwaves | magnetron valve / klystron valve / gun diodes |
$\displaystyle \lambda_{2} \longrightarrow$ & Ultra Violet & high voltage gas discharge tube
\multicolumn{2}{|l|}{$\displaystyle \lambda_{3} \rightarrow$ Infra red} & hot bodies and molecules OR
(i) The two sources should emit the waves in the same phase or with a constant phase difference . The two sources must continuously emit light wave of the same wavelength.
(ii)
| Interference \begin{itemize} \item[1)] Intensity of all bright bands are nearly same \item[2)] All fringes are of same width. \end{itemize} | \begin{itemize} \item[] Diffraction \item[1)] Intensity of bright bands decreases rapidly on both sides of central maxima. \item[2)] All the fringes are not of same width / the width of central maximum is double that of the width of secondary maxima. \end{itemize} |
Or any other two differences.
(ii)
Two points of difference
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CBSE Class 12 Physics past-paper question from the 2022 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.