Exam 18: Electric Currents

The resistivity of gold is $2.44 \times 10 ^ { - 8 } \Omega \cdot \mathrm { m }$ at a temperature of $20 ^ { \circ } \mathrm { C }$ . A gold wire that is $0.50 \mathrm {~mm}$ in diameter and $44 \mathrm {~cm}$ long carries a current of $380 \mathrm {~mA}$ . How many electrons each second pass a given cross section of the wire at $20 ^ { \circ } \mathrm { C } ? \left( e = 1.60 \times 10 ^ { - 19 } \mathrm { C } \right)$

For the graph shown in the figure, what physical quantity does the slope of the graph represent for a dc circuit?

A 25-W soldering iron runs on 110 V dc. What is its resistance?

A $120 - \mathrm { m }$ long metal wire having a resistivity of $1.68 \times 10 ^ { - 8 } \Omega \cdot \mathrm { m }$ has a resistance of $6.0 \Omega$ . What is the diameter of the wire?

A toaster is rated at 800 W when operating at 120 V dc. What is the resistance of its heating element?

A battery is rated such that it provides $1.0 \mathrm {~mW}$ of power at $9.0 \mathrm {~V}$ when fully charged. How much current can it deliver?

The graph shown in the figure shows the results of measurements of the dc current through a circuit device for various potential differences across it. Assume that all the numbers shown are accurate to two significant figures. What is the resistance of this device?

How much current will be flowing through a $57.0 - \mathrm { m }$ length of copper wire with radius $0.0$ mm if it is connected to a source supplying $62.0 \mathrm {~V}$ ? The resistivity of the metal is $1.68 \times 10 ^ { - 8 } \Omega \cdot \mathrm { m }$ .

A $200 - \Omega$ resistor is rated at $1 / 4 \mathrm {~W}$ . What is the maximum voltage that can safely be connected across it?

A metal bar is $20 \mathrm {~cm}$ long and has a rectangular cross-section measuring $1.0 \mathrm {~cm} \times 2.0 \mathrm {~cm}$ . What is the voltage drop along its length when it carries a 4000-A current? The resistivity of the metal is $1.68 \times 10 ^ { - 8 } \Omega \cdot \mathrm { m }$ .

The graph shown in the figure shows the results of measurements of the dc current through a circuit device for various potential differences across it. Assume that all the numbers shown are accurate to two significant figures. What is the resistance of this device?

A light bulb operating at 110 V draws 1.40 A of current. What is its resistance?

When a potential difference is applied across a piece of wire made of metal A, a $5.0 - \mathrm { mA }$ current flows. If the metal-A wire is replaced with a wire made of metal B having twice the diameter of the metal-A wire, how much current will flow through the metal-B wire? The lengths of both wires are the same, and the voltage difference remains unchanged. The resistivity of metal $\mathrm { A }$ is $1.68 \times 10 ^ { - 8 } \Omega \cdot \mathrm { m }$ , and the resistivity of metal $B$ is $1.59 \times 10 ^ { - 8 } \Omega \cdot \mathrm { m }$ .

A battery supplies $6.0 \mathrm {~mA}$ to a $12 - \Omega$ resistor for $1.5 \mathrm {~h}$ . How much electric energy does this resistor dissipate in this time?

A $12 - \mathrm { V }$ battery is connected across a $100 - \Omega$ resistor. How many electrons flow through the wire in $1.0 \mathrm {~min}$ ? $\left( e = 1.60 \times 10 ^ { - 19 } \mathrm { C } \right)$

The figure shows a graph of the resistance of a wire as a function of its length. What physical quantities does the slope of this graph represent?

A total of $2.0 \times 10 ^ { 13 }$ electrons pass a given point in a wire in $15 \mathrm {~s}$ . What is the current in the wire? $\left( e = 1.60 \times 10 ^ { - 19 } \mathrm { C } \right)$

You are given a copper bar of dimensions 3 cm × 5 cm × 8 cm and asked to attach leads to it in order to make a resistor. If you want to achieve the smallest possible resistance, you should attach The leads to the opposite faces that measure

The figure shows electrons passing through a resistor. The arrow shows the direction in which the electrons are moving. Which of the following statements are correct? (There could be more than one correct choice.)

If the power rating of a $400 - \Omega$ resistor is $0.80 \mathrm {~W}$ , what is the maximum current it can safely draw?