Physics 11: Chapter 23 HW

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

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

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

Use the noncontact ammeter to measure the current flowing through the circuit. What is the current? 9 A 0.9 A 10 A 90 A

0.9 A

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

Current = Voltage Difference / Resistance

Why are electrons, rather than protons, the principal charge carriers in metal wires?

Electrons are free to move through the metal, whereas protons are fixed in place

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. (You should be able to answer this question using what you have already learned, but if you want, feel free to build the four circuits and make measurements.)

Greatest Current: 1. Square with 3 boxes 2. Square with two boxes 3. 9.0V, 10.0Ω 4. 9.0V, 10.0Ω, 10.0Ω

Does heating a metal wire increase or decrease its electrical resistance? Why?

It increases resistance because atoms at higher temperatures jostle into the way of moving electrons.

If the resistance of a circuit remains constant while the voltage across the circuit decreases to half its former value, what change occurs in the current

It is cut in half

What does the power company provide to our homes?

It provides energy to move the electrons

Why does a wire that carries electric current become hot?

Moving electrons collide with atoms, which transfers their kinetic energy to atomic motion.

What is the relationship among electric power, current, and voltage?

Power is current times voltage.

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 clicking the Values checkbox in the display at the upper-right corner of the panel. Use the default values of the battery and resistor. You should see the blue electrons flowing through the circuit. In what direction is the (conventional) 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.

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

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

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

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.

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.

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.

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

both the geometry and the material of the conductor

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

continue glowing as brightly

When you make your household electric payment at the end of the month, are you billed for voltage, current, power, or energy?

energy

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

Of what physical quantity is Hertz a unit of?

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

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 orange end

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

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? You should see the blue electrons flowing through the circuit, whereas (conventional) current is the flow of positive charge. You can select which current to display in the panel in the upper-right corner.

9.0 V

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

9.0 V

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

alternating current

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

go out

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

the current decreases.

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

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.

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

current increases

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

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 function of the round third prong in a modern household electric plug?

It grounds the case to zero potential.

Does a battery produce dc or ac? Does the generator at a commercial power station produce dc or ac?

The battery is dc; the generator is ac.

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

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? (Note that the PhET simulation does not display a numerical value for the luminosity, so you should use the relationship between the luminosity, the voltage across the bulb, and the current.)

The luminosity increases by a factor of four.

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 unit of electrical resistance?

ohm

A flow of electric charge in a wire normally requires a _________.

potential difference across the ends of the wire