JEE Main & Advanced Physics Current Electricity, Charging & Discharging Of Capacitors / वर्तमान बिजली, चार्ज और कैपेसिटर का निर JEE PYQ-Current Electricity Charging and Discharging of Capacitors

  • question_answer
    The resistance of an electrical toaster has a temperature dependence given by \[R\,\,(T)={{R}_{0}}[1+\alpha (T-{{T}_{0}}]\] in its range of operation. At \[{{T}_{0}}=300\,K,\,R=100\Omega \]. And at\[T=500\,K,\,R=120\Omega \]. The toaster is connected to a voltage source at 200 V and its temperature is raised at a constant rate from 300 to 500 K in 30s. The total work done in raising the temperature is: [JEE ONLINE 10-04-2016]

    A)             \[400\,In\frac{1.5}{1.3}J\]

    B)             300 J

    C) \[200\,In\frac{2}{3}J\]

    D) \[400\,In\frac{5}{6}J\]

    Correct Answer: D

    Solution :

    [d] Bonus
                    \[\frac{{{(200)}^{2}}}{{{R}_{0}}(1+\alpha (T-{{T}_{0}})}\]
    \[T\to \]temperature at 't'
    \[{{T}_{0}}\to \]temperature at t = 300 K
    \[T-{{T}_{0}}=\frac{500-300}{30}(t)\]
    \[T-{{T}_{0}}=\frac{200}{30}t\]
    \[T-{{T}_{0}}=\frac{20t}{3}\]
    \[\int\limits_{0}^{30}{\frac{{{(200)}^{2}}}{100(1+\alpha \frac{20t}{3})}dt=\frac{200\times 200}{100}\,\,\,\int\limits_{0}^{30}{\frac{dt}{1+\frac{20\alpha }{3}}t}}\]
    \[=\frac{400\times 3}{20\alpha }\ell n\left( \frac{\frac{1+20\alpha }{3}\times 30}{1} \right)\]
    \[120=100\,(1+\alpha (200))\]
    \[1+(200)\alpha =\frac{6}{5}\]
    \[(200\alpha )=\frac{1}{5}\]\[\alpha =\frac{1}{1000}\]
    \[=60,000\,\ell n\left( \frac{6}{5} \right)\]


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