The same mass of copper is drawn into two wires $1\, mm$ and $2\, mm$ thick. Two wires are connected in series and current is passed through them. Heat produced in the wire is in the ratio
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In order to measure the internal resistance $r_1$ of a cell of emf $E$, a meter bridge of wire resistance $R_0=50 \Omega$, a resistance $R_0 / 2$, another cell of emf $E / 2$ (internal resistance $r$ ) and a galvanometer $G$ are used in a circuit, as shown in the figure. If the null point is found at $l=72 cm$, then the value of $r_1=$ . . . . $\Omega$
In a conductor, if the number of conduction electrons per unit volume is $8.5 \times 10^{28}\, m^{-3}$ and mean free time is $25\,fs$ (femto second), its approximate resistivity is $\left( {{m_e} = 9.1 \times {{10}^{ - 31}}\,kg} \right)$
In the adjoining circuit, the galvanometer $G$ shows zero deflection. If the batteries $A$ and $B$ have negligible internal resistance, the value of the resistor $R$ will be .............. $\Omega$
A potentiometer wire of length $100\, cm$ has a resistance of $10\,\Omega $. It is connected in series with a resistance and a cell of $emf$ $2\, V$ and of negligible internal resistance. A source of $emf$ $10\,mV$ is balanced against a length of $40\, cm$ of the potentiometer wire. What is the value of external resistance ? .................. $\Omega$
In a large building, there are $15$ bulbs of $40\ W$, $5$ bulbs of $100\ W, 5$ fans of $80\ W$ and $1$ heater of $1\ kW$. The voltage of electric mains is $220\ V$. The minimum capacity of the main fuse of the building will be ................ $A$
Two resistors $400\, \Omega$ and $800\, \Omega$ are connected in series across a $6 V$ battery. The potential difference measured by a voltmeter of $10\, k \Omega$ across $400\, \Omega$ resistor is close to$....V$