In a potentiometer experiment two cells of $e.m.f.$ $E_1$ and $E_2$ are used in series and in conjunction and the balancing length is found to be $58\, cm$ of the wire. If the polarity of $E_2$ is reversed, then the balancing length becomes $29\, cm$. The ratio $\frac{{{E_1}}}{{{E_2}}}$ of the $e.m.f.$ of the two cells is
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A uniform wire of resistance $9\, ohm$ is bent in the form of a circle. The effective resistance across the points $A$ and $B$ is ............... $\Omega$
A student measures the terminal potential difference $(V)$ of a cell $($ of $emf \;\varepsilon $ and internal resistance $r)$ as a function of the current $(I)$ flowing through it. The slope, and intercept, of the graph between $V$ and $I$, then, respectively, equal
A battery of $e.m.f.$ $10\, V$ is connected to resistance as shown in figure. The potential difference ${V_A} - {V_B}$ between the points $A$ and $B$ is .................... $V$
If a wire of resistance $20\,\Omega $ is covered with ice and a voltage of $210\, V$ is applied across the wire, then the rate of melting of ice is .................. $g/s$
A metal wire of specific resistance $64 \times {10^{ - 6}}\,ohm - cm$ and length $198\, cm$ has a resistance of $7\, ohm$, the radius of the wire will be ............. $cm$
Four lamps are connected in the way shown in the figure. When switch $S_2$ is open and switch $S_1$ is on position $-2$ , lamp $-b$ is the brightest, and lamp $-c$ and lamp $-d$ are the dimmest and are of the same brightness. Now $S_2$ is closed and $S_1$ is on position $-1$ , the sequence in brightness of the lamps is (with the first in the sequence being the brightest)
What is the number density of donor atoms which must be added to a pure germanium semiconductor to make $n-$ type semiconductor of conductivity $6.4\ {\Omega ^{ - 1}}\,c{m^{ - 1}}$? The mobility of electr ons in $n-$ type germanium is $4 \times {10^3}\ cm^2\ V^{-1}\ s^{-1}$. Neglect the contribution of holes to conductivity