Three voltmeters, all having different internal resistances are joined as shown in figure. When some potential difference is applied across $\mathrm{A}$ and $B$, their readings are $V_1, V_2$ and $V_3$. Choose the correct option.
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Two wires of equal diameters, of resistivities ${\rho _1}$ and ${\rho _2}$ and lengths $l_1$ and $l_2$, respectively, are joined in series. The equivalent resistivity of the combination is
In the circuit shown in figure reading of voltmeter is $V_1$ when only $S_1$ is closed, reading of voltmeter is $V_2$ when only $S_2$ is closed. The reading of voltmeter is $V_3$ when both $S_1$ and $S_2$ are closed then
Every atom makes one free electron in copper. If $1.1$ $ampere$ current is flowing in the wire of copper having $1\, mm$ diameter, then the drift velocity (approx.) will be (Density of copper $ = 9 \times {10^3}\,kg\,{m^{ - 3}}$ and atomic weight = $63$)
A platinum resistance thermometer has a resistance of $50\,\Omega $ at $20\,^o C$. When dipped in a liquid the resistance becomes $76.8\,\Omega $. The temperature coefficient of resistance for platinum is $\alpha = 3.92 \times {10^{ - 3}}\,^o C$. The temperature of the liquid is .............. $^o C$
Find the number of photons emitted per second from of source of light which results in a photocurrent with drift velocity of $1.5\ m/s$ in a conductor with cross-section area $0.25\ m^2$ , volume density of electrons $10^{20}\ per \ m^3$ , (Assume that $60\%$ of photons emitted result in electron emission)