The length and area of cross-section of a copper wire are respectively 30 m and $6 \times 10^{-7} \mathrm{~m}^2$. If the resistivity of copper is $1.7 \times 10^{-8} \Omega \mathrm{~m}$, then the resistance of the wire is

If current of 80 A is passing through a straight conductor of length 10 m , then the total momentum of electrons in the conductor is

(mass of electron $=9.1 \times 10^{-31} \mathrm{~kg}$ and charge of electron $=1.6 \times 10^{-19} \mathrm{C}$ )

Charge ' $Q$ ' (in coulomb) flowing through a conductor in terms of time ' $t$ ' (in second) is given by the equation $Q=3 t^2+t$. The current in the conductor at time $t=3 \mathrm{~s}$ is

In a metal, the charge carrier density is $9.1 \times 10^{28} \mathrm{~m}^{-3}$ and its electrical conductivity is $6.4 \times 10^7 \mathrm{~S} \mathrm{~m}^{-1}$. When an electric field of $10 \mathrm{NC}^{-1}$ is applied to the metal, then the average time between two successive collisions of electrons in the metal is

(Mass of electron $=9.1 \times 10^{-31} \mathrm{~kg}$, charge of electron $=1.6 \times 10^{-19} \mathrm{C}$ )