91Ó°ÊÓ

$1.0×{10}^{20}$electrons flow through a cross-section of a $2.0\mathrm{mm}$diameter iron wire in $5.0\mathrm{s}$. What is the electron drift speed?

The current in a $100watt$lightbulb is $0.85\mathrm{A}$. The filament inside the bulb is $0.25\mathrm{mm}$in diameter.

a. What is the current density in the filament?

b. What is the electron current in the filament?

In an integrated circuit, the current density in a $2.5m-thick×75\mathrm{μ}m-wide$wide gold film is localid="1648893767234" $7.5×{10}^5\mathrm{A}/{\mathrm{m}}^2$. How much charge flows through the film in $15\min$?

The current in an electric hair dryer is $10.0\mathrm{A}$. How many electrons flow through the hair dryer in $5.0$min?

Which, if any, of these statements are true? (More than one may be true.) Explain. Assume the batteries are ideal.

a. A battery supplies the energy to a circuit.

b. A battery is a source of potential difference; the potential difference between the terminals of the battery is always the same.

c. A battery is a source of current; the current leaving the battery is always the same.

The current in a$2.0\mathrm{mm}×2.0\mathrm{mm}$square aluminum wire is $2.5\mathrm{A}$. What are (a) the current density and (b) the electron drift speed?

15. A hollow copper wire with an inner diameter of $1.0\mathrm{mm}$and an outer diameter of $2.0\mathrm{mm}$ carries a current of $10\mathrm{A}$. What is the current density in the wire?

16. A car battery is rated at $90\mathrm{Ah}$, meaning that it can supply a $90A$ current for $1\mathrm{h}$ before being completely discharged. If you leave your headlights on until the battery is completely dead, how much charge leaves the battery?

17. What is the mean time between collisions for electrons in (a) an aluminum wire and (b) an iron wire?

19. A$15$-cm-long nichrome wire is connected across the terminals of a $1.5\mathrm{V}$ battery.
a. What is the electric field inside the wire?
b. What is the current density inside the wire?
c. If the current in the wire is $2.0\mathrm{A}$, what is the wire's diameter?