Chapter 23

Consider the power dissipated by the two circuits in the video. The ratio of power dissipation in the parallel circuit to that in the series circuit is

9

For the circuit containing one resistor and one battery, what happens to the current if the voltage is tripled and the resistance is doubled?

The current increases

For the circuit containing one resistor and one battery, what happens to the current if the voltage is doubled?

The current increases by a factor of two

Two lamps with different filament thicknesses, and therefore different resistances, are connected in series. Greater current is in the lamp with the

same in each

A heater draws 20A when connected to a 110-V line. If the electric power costs 20 cents per kilowatt hour, the cost of running the heater for 10 hours is

$4.40

When the filament breaks in one lamp in a series circuit, other lamps in the circuit normally

go out

If the resistivity of copper is less than that of gold at room temperature, which of the following statements must be true?

Electrons in gold are more likely to be scattered than electrons in copper at room temperature when they are accelerated by the same electric field

At what speed do electrons in a battery driven automotive circuit travel along a wire? At what speed does the electric field propagate along a wire?

Electrons move at 0.01 cm/s. The electric field propagates at nearly the speed of light

The current through each resistor in the two-resistor circuit is _________ the current through the resistor in the one-resistor circuit (the circuit in Part A). The voltage across each resistor in the two-resistor circuit is ___________ the voltage across the resistor in the one-resistor circuit.

half / half

When a pair of identical resistors are connected in series, which of the following is the same for both resistors? Do any of your answers change if the resistors are different from each other? Check all that apply.

-voltage across each -power dissipated in each -current through each

Use the noncontact ammeter to measure the current flowing through the circuit. What is the current?

0.9 A

A 60-W and a 100-W light bulb are connected in parallel to a 120-V outlet. Which bulb draws more current?

100-W bulb

How much energy is supplied to each coulomb of charge that flows through a 12-V battery?

12 joules

What is the current in a bulb if the resistance of its filament is 2 ohms and it is connected across a 6-volt battery?

3 amps

What must be the resistance of a single resistor connected to a 9-V battery for the current coming out of the battery to be the same as that of the circuit in Part D?

30 Ω

An electric current of 5 amperes in a wire carries

5 coulombs per second

For the series circuit in the previous part, change the resistance of the bottom resistor to 20 Ω. What is the voltage across this 20-Ω resistor?

6.0 V

With the switch open, roughly what must be the resistance of the resistor on the right for the current out of the battery to be the same as when the switch is closed (and the resistances of the two resistors are 20 Ω and 10 Ω)?

7 Ω

Let's start with a simple circuit that you will have seen in the Ohm's Law and Power PhET tutorial, if you completed that one. What is the voltage reading across the resistor, as shown in the figure below?

9.0 V

What is the voltage reading across the resistor, as shown in the figure below?

9.0 V

A diode converts ac to pulsed dc. What electrical device smoothes the pulsed dc to a smoother dc?

A capacitor

What condition is necessary for the flow of heat? What analogous condition is necessary for the flow of charge?

A difference in temperature is needed for heat to flow. A difference in electrical potential is needed for charge to flow.

Between a watt, a kilowatt, and a kilowatt-hour, which is a unit of power and which is a unit of energy?

A watt is power, a kilowatt is power, and a kilowatt-hour is energy.

Rank the circuits illustrated according to the brightness of the identical bulbs, from brightest to dimmest.

All 3 go in the middle

Does electric charge flow across a circuit or through a circuit? Does voltage flow across a circuit or is it impressed across a circuit?

Charge flows through and voltage is impressed across a circuit

What is the relationship between current, resistance, and voltage difference?

Current = Voltage Difference / Resistance

Which of the following would double the amount of current flowing through a piece of metal wire?

Double the voltage across it

All bulbs are identical in the following circuits. A voltmeter is connected across a single bulb to measure the voltage drop across it. Rank the voltage readings from greatest to least.

Greatest -A (1 yellow bulb) -B (2 yellow bulbs) -C (3 yellow bulbs) Least

Rank the current readings in the ammeter, from greatest to least.

Greatest C (3 layers) B (2 layers) A (1 layer) Least

The figures below show four circuits, with the resistances of the resistors given. In all cases, the emf of the battery is 10 V. Rank the circuits in order of descending total current coming out of the battery.

Greatest current -3 squares -2 squares -biggest square -medium square Smallest current

Do any of your answers change if the resistors are different from each other?

If the resistors are different from each other, the voltage remains the same, the difference in power is dissipated, and the currents will flow differently through them. If resistors are identical then power, current, and voltage are all the same. If the resistors are different the current through the resistors would be the same.

What property of a diode enables it to convert ac to pulsed dc?

It is a one-way valve that allows electrons to in one direction only

What does the power company provide to our homes?

It provides energy to move the electrons

You are given three pieces of wire that have different shapes (dimensions). You connect each piece of wire separately to a battery. The first piece has a length L and cross-sectional area A. The second is twice as long as the first, but has the same thickness. The third is the same length as the first, but has twice the cross-sectional area. Rank the wires in order of which carries the most current (has the lowest resistance) when connected to batteries with the same voltage difference.

Most Current -Wire of length L and area 2A -Wire of length L and area A -Wire of length 2L and area A Least Current

What is the unit of electrical resistance?

Ohm

The brightness of a light bulb having a specific resistance increases if the current through it increases. For the circuit shown in the figure below, how does the brightness of the light bulb change when the resistance of the 10-Ω resistor is decreased?

The brightness does not change

How does the current change if you increase the resistance, keeping the voltage difference the same?

The current decreases

Double the resistance of the resistor by changing it from 10 Ω to 20 Ω. What happens to the current flowing through the circuit?

The current decreases by a factor of two

For the circuit in the previous part, what happens to the current flowing through the resistor on the right when the switch is closed (allowing current to flow through the resistor on the left)?

The current flowing through the resistor on the right does not change

Construct a circuit containing one battery, one resistor, and wire to close the circuit. The order and orientation doesn't matter, but it should look something like the figure below. You can show the values of the components by right-clicking (control-clicking) on each component and selecting Show Value in the pop-up menus. Use the default values of the battery and resistor. You should see the blue electrons flowing through the circuit. In what direction is the current flowing through the circuit? Recall that current is the flow of positive charge.

The current flows from the positive terminal, through the wires and resistor, and into the negative terminal.

Construct a circuit having two resistors connected in parallel, as shown in the figure below. Change the value of the battery emf to 10.0 V, and make sure the middle resistor is set to 20 Ω. Use extra wire for each "leg" of the circuit so you can measure the current through all legs with the ammeter. How does the current coming out of the battery change when the switch is closed?

The current increases

Construct a circuit containing two 10-Ω resistors in series, as shown below. Place the crosshairs of the noncontact ammeter just before each resistor to measure the current through the top and bottom resistors. How do these currents compare?

The currents are the same

What exactly is an ampere?

The flow of one coulomb per second

A light bulb is basically a resistor that gets so hot that it glows, emitting light. For this tutorial we will assume the resistor in the light bulb is ohmic (that means Ohm's law applies to the resistor). The rate of energy emitted by the light bulb is its output power, commonly referred to as luminosity (brighter means more luminous). Hook up a light bulb to a 5-V battery. Right-click (or control-click) on the light bulb, and change its resistance. How does the brightness of the light bulb depend on its resistance?

The light bulb gets dimmer as the resistance is increased.

In Part H, you discovered that the luminosity of a light bulb increases if the current increases. The rate at which electric potential energy is converted into heat depends on the current flowing through the bulb and the voltage across the bulb. This energy is supplied by the battery. Mathematically, the luminosity P of the light bulb is given by P=ΔVI, where ΔV is the voltage across the bulb and I is the current. What happens to the luminosity of the light bulb if the voltage of the battery is doubled?

The luminosity increases by a factor of four

Now, we'll add a bulb in parallel to the capacitor. Build the circuit shown in the figure (you'll need to close the switch to charge the capacitor and light the bulb). What happens to the luminosity (or brightness) of the bulb when the switch is then opened?

The luminosity is initially the same as before the switch is closed, but then gradually fades to zero

How does the resistance of a thick piece of copper wire compare to the resistance of a thin piece of copper wire?

The resistance of the thin piece is greater than that of the thick piece

Long after the switch is closed and the current becomes very small, what is the voltage difference across the capacitor?

The same as the emf of the battery

How do the currents through the branches of a simple parallel circuit compare with the current in the voltage source?

The sum of the currents in the branches equals the current through the source

How do the resistances of two conducting wires compare if they have the same length, but one is twice the radius of the other?

The thicker wire has one-fourth the resistance of the thinner wire

With the switch closed, how does the voltage across the 20-Ω resistor compare to the voltage across the 10-Ω resistor?

The voltage across the 20-Ω resistor is equal to the voltage across the 10-Ω resistor

What is the function of fuse or circuit breaker in a circuit?

To prevent over loading the circuit with current

Electrons flow in a wire when there is

a potential difference across its ends

What kind of current runs through the electric wiring in a home?

alternating current

The equivalent resistance of any parallel branch in a circuit is

always less than the resistance of the lowest resistor

If you wish to keep chicken warm in a shed on a cold night, the best lamp to use is

an incandescent lamp

In a circuit powered by a battery, charge

both of these (is energized by the battery, flows through the battery)

What factors does the resistance offered by a piece of conductor depend upon?

both the geometry and the material of the conductor

A 60-W and a 100-W light bulb are connected in series to a 120-V outlet. Which bulb draws more current?

both the same

The electric field established by a generator in an ac circuit

changes magnitude and direction with time

Which statement is correct?

charge flows in a circuit

When the filament breaks in one lamp in a parallel circuit, lamps in other branches of the circuit normally

continue glowing as brightly

When your body undergoes electric shock, the source of moving electrons is

electrons already in your body

The entity that travels about the speed of light in an electric circuit is

electric field

What type of field causes the electrons to do what they do in the wire?

electric field

Electric power in a circuit is the rate at which

energy dissipates

For the circuit in the previous part, the current flowing in the wire between the positive terminal of the battery and the resistor is ___________ the current flowing between the resistor and the negative terminal of the battery.

equal to

Now, repeat the experiment several times to investigate how the amount of time to charge the capacitor (resulting in a voltage difference equal to the emf of the battery) depends on the capacitance of the capacitor and the resistance of the resistor. Each time you repeat the experiment, you first need to open the switch and right-click or control-click on the capacitor to select Discharge Capacitor. The amount of time ________ if the resistance is increased and ________ if the capacitance is increased.

increase / increases

As more lamps are connected in a parallel circuit, the overall current in the power source

increases

Electrons flow in an electrical circuit by

interacting with an established electric field

For the parallel circuit in the previous part (with the switch closed), the current through the 20-Ω resistor is _________ the current through 10-Ω resistor.

less than

When two lamps are connected in parallel to a battery, the electrical resistance that the battery senses is

less than the resistance of either lamp

When two lamps are connected in series to a battery, the electrical resistance that the battery senses is

more than the resistance of either lamp

Of what physical quantity is Hertz a unit of?

number of times per second that the electrons move back and forth in the wire

A flow of electric charge in a wire normally requires a

potential difference across the ends of the wire

A voltage source in a circuit provides electrical

pressure

Drag a battery into the construction panel, and use the voltmeter to determine which end of the battery is the positive terminal. The positive terminal has a higher potential than the negative terminal (recall that the voltmeter measures the potential difference between the red probe and the black probe). Which end of the battery is the positive terminal?

the black end

The source of energy that illuminates a lamp in your home is

the power company

Construct a circuit containing a battery, a resistor, a switch, and a capacitor (all in series), as shown in the figure. Be sure the switch is open (which stops current through the switch) before you connect up the entire circuit. Now, close the switch and monitor the resulting current through the circuit. After the switch is closed,

there is initially a current, but it decreases with time and eventually stops

The electric resistance in a length of wire is doubled when the wire is

twice as long

Electrons in the filament of a lamp that carries ac have a net speed that is

zero