Physics Chapter 23- Electric Current

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What exactly is an ampere

The flow of one coulomb per second

Just as water flows from a region of high pressure to a region of low pressure, electric charge flows from a region of

high electric pressure to a region of low electric pressure

Voltage is most similar to


The current produced by voltage in a circuit is impeded by

electric resistance

Ohm’s law tells us that the amount of current produced in a circuit is

directly proportional to voltage and inversely proportional to resistance

The resistance of a filament that carries 2 A when a 10-V potential difference across it is

5 ohms

Direct current is normally produced by a


Alternating current is normally produced by a


For electric current in the home, your power company supplies


The cause of electrical shock is predominantly

excess voltage

One joule per coulomb is a unit of


One kilowatt is a unit of


One kilowatt-hour is a unit of


When a 12-V battery powers a single 6-ohm lamp

12 joules flow in the lamp each second

By convention, the direction of current in a circuit is

The direction in which positive charge flows and, from the positive terminal of a source to the negative terminal.

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

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 a pair of identical lamps are connected in parallel

Voltage across each is the same Current in each is the same and Power dissipated in each is the same

Connect a pair of lamps in series and current is drawn from the battery. Connect the same lamps in parallel and the current drawn is


The force that acts between a pair of magnetic poles depends on

separation distance and magnetic pole strength

Whereas electric charges can be isolated, magnetic poles

can not

Surrounding every magnet is

a magnetic field

The conventional direction of magnetic field lines outside a magnet are from

north to south

The end of a compass needle that points to the south pole of a magnet is the

north pole

The lift experienced by Maglev trains is due to magnetic


When current reverses direction in a wire, the surrounding magnetic field

also reverses direction

When a current-carrying wire is bent into a loop, its magnetic field inside the loop

becomes concentrated

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.

What condition is necessary for the sustained flow of water in a pipe? What analogous condition is necessary for the sustained flow of charge in a wire

A continuous pressure difference, often provided by a pump, is needed for water to flow. A continuous potential difference, often provided by a battery, is needed for charge to flow

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

12 joules

Name two kinds of practical "electric pumps.

Batteries and automobile alternators

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

Current = Voltage Difference / Resistance

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

The current decreases

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

both the geometry and the material of the conductor

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 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

If the voltage impressed across a circuit is held constant while the resistance doubles, what change occurs in the current

It is cut in half

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

It grounds the case to zero potential

What does the power company provide to our homes

It provides energy to move the electrons

Of what physical quantity is Hertz a unit of

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

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

electric field

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

alternating current

Electrons flow in a wire when there is

a potential difference across its ends

To think of electric potential difference we are thinking about


The unit of electrical resistance is the


Heat a copper wire and its electric resistance


Current in a conductor can be increased by

reducing its resistance and increasing the voltage across it

The power consumed by a device drawing 0.8 A when connected to 120 V is


The brightness of a lamp is directly related to its

power rating

What is the source of the magnetic force

Electric charges in motion are the sources of magnetic forces

How is the rule for the interaction between magnetic poles similar to the rule for the interaction between electrically charged particles

Like poles repel, unlike poles attract, and the force is proportional to the inverse square of the distance between two poles

In what way are magnetic poles very different from electric charges

All magnets have both south and north poles. Electric charges can exist as singular entities.

Why will dropping an iron magnet on a concrete sidewalk make it a weaker magnet

Vibrations provide energy to randomize the magnetic directions of the domains

Why is the magnetic field strength greater inside a current-carrying loop of wire than about a straight section of wire

The magnetic field of each segment of wire in the loop, due to electrons moving in the wire, adds together inside the loop, thereby making the field become bunched-up

Like kinds of magnetic poles repel while unlike kinds of magnetic poles


In general, a common magnet has

at least two poles

Magnetic domains normally occur in


Wood does not have magnetic properties because it contains no

magnetic domains

Into which stable force field can a proton be placed at rest without being acted upon by a force

magnetic field

Potential Difference

The difference in electric potential between two points, measured in volts

Electric Current

The flow of electric charge that transports energy from one place to another, measured in amperes, where 1 A is the flow of 6.25 * 10^18 electrons per second or 1 coulomb per second

Electrical Resistance

The property of a material that resists electric current, measured in ohms

Ohm’s Law

The statement that the current in a circuit varies in direct proportion to the potential difference or voltage across the circuit and inversely with the circuit’s resistance. Current = voltage/resistance A potential difference of 1 V across a resistance of 1 ohm produces a current of 1 A

Direct Current (dc)

Electrically charged particles flowing in one direction only

Alternating Current (ac)

Electrically charged particles that repeatedly reverse direction, vibrating about relatively fixed positions. In the United States, the vibrational rate is commonly 60hz

Electric Power

The rate of energy transfer, or the rate doing work; the amount of energy per unit time, which can be computed as the product of current and voltage Power=current * voltage Electric power is measured in watts or kilowatts where 1 W= 1A * 1V= 1J/s

Series Circuit

An electric circuit in which electrical devices are connected along a single loop of wire such that the same current is in each device

Parallel Circuit

An electric circuit in which electrical devices are connected in such a way that the same voltage acts across each one, and any single one completes the circuit independently of all other

In a circuit of two lamps in series, where the current through one lamp is 1 A, what is the current through the other lamp? Defend your answer.

1 amp. The same current flows through lamps in series

Electric power in a circuit is the rate at which

energy dissipates

Will water flow more easily through a wide pipe or a narrow pipe? Will current flow more easily through a thick wire or a thin wire

Wide pipe and thick wire

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

electrons already in your body

In a circuit of two lamps in parallel, where there is a voltage of 6 V across one lamp, what is the voltage across the other lamp?

6 volts

A flow of electric charge in a wire normally requires a

potential difference across the ends of the wire

The voltage across a 10-ohm resistor carrying 5 A is

more than 20 V

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 unit of electrical resistance


Using the formula power = current × voltage, find the current drawn by a 1000-W toaster connected to 140V

W/V 1000W/140V

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

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

Power is current times voltage

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

go out

If a voltage of 6 V is impressed across the circuit in the preceding question and the voltage across the first lamp is 2 V, what is the voltage across the second lamp? Defend your answer.

4 volts. The sum of the voltages across each lamp must add up to the total voltage across both lamps.

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 it mean to say that a certain current is 60 Hz?

It alternates back and forth 60 times a second

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

continue glowing as brightly

A voltage source in a circuit provides electrical


A 60-W light bulb connected to a 120-V source draws a current of

W/V =I(A) 60W/120V = 0.5 I (A)

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

electric field

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

twice as long

Two light bulbs are connected to a battery, one at a time. The bulb that draws more current has the

lower resistance, and is brightest

What happens to the direction of the magnetic field about an electric current when the direction of the current is reversed

The magnetic field reverses direction at every point. A clockwise pattern of concentric circles becomes a counterclockwise pattern of concentric circles and vice versa

Magnetic field strength about a magnet is strongest where magnetic field lines are

closer together

How does magnetic field strength relate to the closeness of magnetic field lines about a bar magnet

the field strength is stronger where the field lines are closer

The fundamental rule for the attraction and repulsion of magnets is that

like poles repel each other while opposite poles attract

Why is iron magnetic and wood not

The magnetic fields of individual iron atoms are strong enough to align the magnetic fields of neighbor atoms. The atoms in wood have much weaker magnetic fields.

What is a magnetic domain

Clusters of atoms with their magnetic fields aligned

An iron rod becomes magnetic when

the net spins of many of its electrons are aligned

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