Current Density — Prelims Questions

A copper wire of radius $1,\text{mm}$ carries a current of $2.2,\text{A}$. If the number of free electrons per unit volume in copper is $8.5 \times 10^{28},\text{m}^{-3}$, what is the drift velocity of the electrons? (Given: charge of an electron $e = 1.6 \times 10^{-19},\text{C}$)

A conductor of resistivity $1.7 \times 10^{-8},Omega \cdot \text{m}$ has an electric field of $0.05,\text{V/m}$ applied across it. What is the current density in the conductor?

A current of $10,\text{A}$ flows through a conductor. If the current density at a particular cross-section is $2.5 \times 10^6,\text{A/m}^2$, what is the area of that cross-section?

Which of the following statements about current density is INCORRECT?

A wire of length $L$ and uniform cross-sectional area $A$ has a current $I$ flowing through it. If the wire is stretched to twice its original length, assuming its volume remains constant, what happens to the current density if the same current $I$ is maintained?

If the electric field inside a conductor is doubled, and the material's conductivity remains constant, what happens to the current density?