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A capacitor of capacitance C=.015F is connected to parallel conducting rail and a conducting rod of mass m=100g and length l=1m start the fall under gravity in vertical plane. A  uniform magnetic field of 2T exist in space direction perpendicular to rod as shown in figure. Find acceleration of rod. 

                                                               

A) 6.25

B) 1.69

C) 1.44

D) 2.25

 

 

Answers (1)

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\begin{array}{l} \mathrm{E}=\mathrm{B} \mathrm{lV} \\ \mathrm{Q}=\mathrm{CE} \\ =\mathrm{BlV} \mathrm{C} \\ \mathrm{i}=\frac{\mathrm{dQ}}{\mathrm{dt}}=\mathrm{BlC} \frac{\mathrm{dV}}{\mathrm{dt}} \\ \Rightarrow \mathrm{F}_{\mathrm{b}}=\mathrm{Bil} \end{array}

\begin{aligned} &=\mathrm{B} \cdot \mathrm{B} \mathrm{lC}\left(\frac{\mathrm{d} \mathrm{V}}{\mathrm{dt}}\right)^{1}\\ &=\mathrm{B}^{2} \mathrm{l}^{2} \mathrm{C}\left(\frac{\mathrm{d} \mathrm{V}}{\mathrm{dt}}\right)\\ &\therefore \mathrm{mg}-\mathrm{B}^{2} \mathrm{l}^{2} \mathrm{C} \cdot \mathrm{a}=\mathrm{ma}\\ &\Rightarrow \mathrm{mg}-\left(\mathrm{m}+\mathrm{B}^{2} \mathrm{l}^{2} \mathrm{C}\right) \mathrm{C} \end{aligned}

\large \begin{array}{l} \Rightarrow \mathrm{a}=\frac{\mathrm{mg}}{\mathrm{m}+\mathrm{B}^{2} \mathrm{l}^{2} \mathrm{C}}=\frac{1}{\frac{100}{1000}+4 \times 1^{2} \times \frac{15}{1000}} \\ =\frac{1000}{160} \mathrm{m} / \mathrm{s}^{2} \\ =6.25 \mathrm{m} \end{array}

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avinash.dongre

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