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Physics · 2024 · 4 marks
CBSE 2024 · Region 3 · Set 1 · Q29
The figure shows four pairs of parallel identical conducting plates, separated by the same distance 2.0 cm and arranged perpendicular to x -axis. The…
The figure shows four pairs of parallel identical conducting plates, separated by the same distance $\displaystyle 2.0$ cm and arranged perpendicular to x -axis. The electric potential of each plate is mentioned. The electric field between a pair of plates is uniform and normal to the plates.
(i)
For which pair of the plates is the electric field $\displaystyle \overrightarrow{\mathrm{E}}$ along $\displaystyle \hat{\mathrm{i}}$ ?
(A)
I
(B) II
(C)
III
(D)
IV
(ii)
An electron is released midway between the plates of pair IV. It will :
(A)
move along $\displaystyle \hat{\mathrm{i}}$ at constant speed
(B)
move along $\displaystyle -\hat{\mathrm{i}}$ at constant speed
(C)
accelerate along $\displaystyle \hat{\mathrm{i}}$
(D)
accelerate along $\displaystyle -\hat{\mathrm{i}}$
(iii)
Let $\displaystyle \mathrm{V}_{0}$ be the potential at the left plate of any set, taken to be at $\displaystyle \mathrm{x}=0 \mathrm{~m}$. Then potential V at any point $\displaystyle (0 \leq \mathrm{x} \leq 2 \mathrm{~cm})$ between the plates of that set can be expressed as :
(A)
$\displaystyle \mathrm{V}=\mathrm{V}_{0}+\alpha \mathrm{x}$
(B)
$\displaystyle \mathrm{V}=\mathrm{V}_{0}+\alpha \mathrm{x}^{2}$
(C)
$\displaystyle \mathrm{V}=\mathrm{V}_{0}+\alpha \mathrm{x}^{1 / 2}$
(D)
$\displaystyle \mathrm{V}=\mathrm{V}_{0}+\alpha \mathrm{x}^{3 / 2}$ where $\displaystyle \alpha$ is a constant, positive or negative.
(iv)
Let $\displaystyle \mathrm{E}_{1}, \mathrm{E}_{2}, \mathrm{E}_{3}$ and $\displaystyle \mathrm{E}_{4}$ be the magnitudes of the electric field between the pairs of plates, I, II, III and IV respectively. Then :
(A)
$\displaystyle \mathrm{E}_{1}>\mathrm{E}_{2}>\mathrm{E}_{3}>\mathrm{E}_{4}$
(B)
$\displaystyle \mathrm{E}_{3}>\mathrm{E}_{4}>\mathrm{E}_{1}>\mathrm{E}_{2}$
(C)
$\displaystyle \mathrm{E}_{4}>\mathrm{E}_{3}>\mathrm{E}_{2}>\mathrm{E}_{1}$
(D)
$\displaystyle \mathrm{E}_{2}>\mathrm{E}_{3}>\mathrm{E}_{4}>\mathrm{E}_{1}$
An electron is projected from the right plate of set I directly towards its left plate. It just comes to rest at the plate. The speed with which it was projected is about : (Take $\displaystyle (\mathrm{e} / \mathrm{m})=1.76 \times 10^{11} \mathrm{C} / \mathrm{kg}$ )
(A)
$\displaystyle 1.3 \times 10^{5} \mathrm{~m} / \mathrm{s}$
(B)
$\displaystyle 2.6 \times 10^{6} \mathrm{~m} / \mathrm{s}$
(C)
$\displaystyle 6.5 \times 10^{5} \mathrm{~m} / \mathrm{s}$
(D)
$\displaystyle 5.2 \times 10^{7} \mathrm{~m} / \mathrm{s}$
Marking-scheme solution
(i)(D)
IV
(ii)(D)
accelerate along \(\displaystyle -\hat{i}\)
(iii)(A)
\(\displaystyle V = V_0 + \alpha x\)
(iv)
(a)
(C) \(\displaystyle E_4 > E_3 > E_2 > E_1\)
OR
(b)
(B) \(\displaystyle 2.6 \times 10^{6}\ \text{m/s}\)
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