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In $a$ wire of cross-section radius $r$, free electrons travel with drift velocity $v$ when a current $I$ flows through the wire. What is the current in another wire of half the radius and of the same material when the drift velocity is $2v$?
Resistances are arranged in a cyclic order to form a balanced wheatstone bridge as shown in figure. Ratio of power consumed in the branches $P + Q$ and $R + S$ is
A cylindrical copper rod has length $L$ and resistance $R$. If it is melted and formed into another rod of length $2 L$, then the resistance will be ....... $R$
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
One $kg$ of water, at $20\,^oC$, is heated in an electric kettle whose heating element has a mean (temperature averaged) resistance of $20\, \Omega $. The rms voltage in the mains is $200\, V$. Ignoring heat loss from the kettle, time taken for water to evaporate fully, is close to.......... $\min$ [Specific heat of water $= 4200\, J/kg\, ^oC$), Latent heat of water $= 2260\, k\,J/kg$]
A constant electric current $I$ is passed through a straight conductor of length $l$. If $S$ in specific charge of electron then the total momentum of electrons is