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A resistor develops $300 \,J$ of thermal energy in $15 \,s$, when a current of $2\, A$ is passed through it. If the current increases to $3 \,A$, the energy developed in $10\,\,s$ is........$J.$
A copper wire of length $1\, m$ and radius $1\, mm$ is joined in series with an iron wire of length $2\, m$ and radius $3\, mm$ and a current is passed through the wires. The ratio of the current density in the copper and iron wires is
Two sources of equal $emf$ are connected to an external resistance $R$. The internal resistances of the two sources are ${R_1}$ and ${R_2}\,({R_2} > {R_1})$. If the potential difference across the source having internal resistance ${R_2}$ is zero, then
In a potentiometer arrangement. $E_1$ is the cell establishing current in primary circuit. $E_2$ is the cell to be measured. $AB$ is the potentiometer wire and $G$ is a galvanometer. Which of the following are the essential condition for balance to be obtained.
Figure shows a thick shell made of electrical conductivity $\sigma$ and has inner & outer radii of $10\ cm$ & $20\ cm$ respectively and is filled with ice inside it. Its inside and outside surface are kept at different potentials by a battery of internal resistance $\frac{2}{\pi} \Omega \ \&\ \epsilon = 5V$. Find value of $\sigma$ for which ice melts at maximum possible rate if $25\%$ of heat generated by shell due to joule heating is used to melt ice.
In the fig. shown for given values of $R_1$ and $R_2$ the balance point for jockey is at $40\, cm$ from $A$. When $R_2$ is shunted by a resistance of $10\,\Omega $, balance shifts to $50\, cm. R_1$ and $R_2$ are $(AB = 1\,m)$
A potentiometer is used for the comparison of $e.m.f.$ of two cells ${E_1}$ and ${E_2}$. For cell ${E_1}$ the no deflection point is obtained at $20\,cm$ and for ${E_2}$ the no deflection point is obtained at $30\,cm$. The ratio of their $e.m.f.$'s will be
In an experiment of potentiometer for measuring the internal resistance of primary cell a balancing length $\ell $ is obtained on the potentiometer wire when the cell is open circuit. Now the cell is short circuited by a resistance $R$. If $R$ is to be equal to the internal resistance of the cell the balancing length on the potentiometer wire will be