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Physics · 2023 · 4 marks
CBSE 2023 · Region 3 · Set 1 · Q34
A beam of electrons moving horizontally with a velocity of 3 × 10^7 m / s enters a region between two plates as shown in the figure. A suitable…
A beam of electrons moving horizontally with a velocity of $\displaystyle 3 \times 10^{7} \mathrm{~m} / \mathrm{s}$ enters a region between two plates as shown in the figure. A suitable potential difference is applied across the plates such that the electron beam just strikes the edge of the lower plate.
Answer the following questions based on the above :
(a)
How long does an electron take to strike the edge ?
(b)
What is the shape of the path followed by the electron and why ?
(c)
Find the potential difference applied.
OR
(c)
Find the magnitude and direction of the magnetic field which should be created in the space between the plates so that the electron beam goes straight undeviated.
Marking-scheme solution
(a)
Electron strikes the edge after travelling $\displaystyle 3$ cm horizontally (along x-axis).
\[\begin{aligned}
& \mathrm{S}_{\mathrm{x}}=\mathrm{v}_{\mathrm{x}} \times \mathrm{t} \\
& 3 \times 10^{-2}=\left(3 \times 10^{7}\right) \times \mathrm{t} \\
& \mathrm{t}=10^{-9} \mathrm{~s}
\end{aligned}
\]
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CBSE Class 12 Physics past-paper question from the 2023 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.