SmartBook: Electric Current and Circuit

1.9 V

A 4.5-V battery and two resistors, 26 Ω and 19 Ω, are connected as a voltage divider. What is the potential difference across the 19-Ω resistor?

4.49 V

A battery delivers a 1.57-A current to a fluorescent light bulb. In 3.00 min it delivers 1.27 kJ of electrical energy. What potential difference does the battery create?

Blank 1: potential Blank 2: 12 Blank 3: J, Joules, or joules

A battery that creates a(n) ____ difference of 12 V does ____ ____ of work on each coulomb of charge.

Blank 1: voltage Blank 2: divider

A circuit arrangement producing a source of potential difference that is less than the potential difference across the battery is a(n)

series

A connection with only one current path in a circuit is a(n) ____ connection.

resistor

A device designed to have a specific resistance is a(n)

electric current

A flow of charged particles is defined as a(n)

by melting and stopping currents passing through it that are too large, exceeding a threshold value.

A fuse is a short piece of metal that acts as a safety device

6.91 × 10^5 J

A heater has a resistance of 15.0 Ω and operates with a current of 8.00 A. How much thermal energy does the heater supply in 12.0 min?

parallel

A type of connection in which there are two or more current paths to follow is a(n) ____ connection

is less than the potential difference across the battery.

A voltage divider produces a source of potential difference that

the sum of decreases in electric potential around that loop.

According to the loop rule, the sum of increases in electric potential around a loop in an electric circuit equals

Blank 1: electrical Blank 2: kinetic Blank 3: thermal

An electric motor transforms ____ energy into ____ energy, but some energy is lost through transformation into _____ energy.

Blank 1: kilowatt Blank 2: hour

An energy unit equal to 1000 watts delivered continuously for 3600 s (1 h), or 3.6 × 106 J, is defined as a(n) ____ ____

Blank 1: superconductors Blank 2: plants Blank 3: MRI

At present, almost no ____ operate above 100 K, so they cannot be used to carry electrical power from power ____ to consumers, but they can be used in applications such as _____ (magnetic resonance imaging) magnets.

Blank 1: resistance Blank 2: conductors Blank 3: Ohm's

Different materials have different properties of ____, or resistivities. Metallic ____ generally obey _____ law, but many devices contain transistors and diodes, which do not obey it.

The vertical distance the river drops is like potential difference in the circuit. Both rivers and circuits can take multiple paths. Both rivers and circuits have a source.

How is a circuit like a river?

Multiply its rate of energy consumption in watts by the number of seconds it is in operation.

How is the electrical energy used by a device usually determined?

Blank 1: closed Blank 2: movement Blank 3: current

If a _____ path for the _____ f charged particles contains a charge pump, then a flow of charged particles, or an electric ____, is created.

400,000 Ω

If a typical photoresistor has a resistance of 400 Ω when light is striking it, which could be its resistance when it is in the dark?

The bulbs will glow with equal brightness.

If you connect two bulbs in series, how will they compare in brightness?

equivalent resistance.

If you replaced all the resistors in a circuit with a single resistor that resulted in the same current, that resistor's value would be the

The current does not change.

In a parallel circuit with two resistors on different paths, what happens to the current through one resistor when the other resistor is removed?

series

In a(n) ____ circuit, the current is the same everywhere in the circuit.

21 A

In the circuit shown, R1 = 12 Ω, R2 = 8 Ω, and R3 = 4 Ω. The potential difference is 45 V. What is the current across the battery?

Blank 1: water or river Blank 2: flow or amount Blank 3: small, smaller, or lesser Blank 4: total

In the mountain river model, the circuit shown is illustrated by three paths for the ____ over a waterfall. Some paths might have a large ____ of water, while others might have a(n) ____ flow. The sum of the water in the flows, however, is equal to the ____ flow of water over the falls.

7.5 A

In the parallel circuit, the generator creates a potential difference of 120 V. If R1 = 16 Ω, R2 = 16 Ω, and R3 = 8 Ω , what is the current through R1?

- A motor in an electric circuit and a waterwheel in a waterfall both depend on converting forms of potential energy into mechanical energy. - Moving water powers a waterwheel just as moving charges in an electric current power a motor.

In which ways are electric current and water flow comparable?

1 battery 2 lamp 3 voltmeter 4 ammeter

Place the components in the circuit in the same order as the direction of conventional current flow, starting with the electron source. For parallel connections, put the meter component first.

battery

Several galvanic cells connected together are called a(n)

Blank 1: variable Blank 2: coil Blank 3: increases Blank 4: current

Some ____ resistors consist of a(n) _____ of resistance wire and a moveable contact point. As the contact point shifts to include more wire in the circuit, its resistance ____, reducing the ____ that flows.

Blank 1: current Blank 2: potential Blank 3: equivalent

The ____ in a series circuit can be calculated by dividing the _____ difference across the power source by the _____ resistance of the circuit.

Blank 1: potential Blank 2: potential Blank 3: kinetic

The charge pump in an electric circuit transforms mechanical or chemical energy to increase the electric ______ energy of the charges flowing in it. Devices in the circuit transform some of this electric _____ energy to forms of energy such as ____ energy in a motor or light energy in a lamp.

P = I^2R P = (ΔV2)/R

The rate of energy transformation in a resistor is given by which equations?

The current is doubled.

The resistance in a circuit is halved while the potential difference is unchanged. What happens to the current?

Blank 1: photoresistor Blank 2: output or voltage Blank 3: divider

The resistance of a(n) ____ depends on the amount of light that strikes it. This alters the ____ of the voltage ____ that is being used with the device.

Blank 1: increases Blank 2: sum Blank 3: potential

The sum of ____ in electric potential around a loop in an electric circuit equals the ____ of decreases in _____ electric around that loop.

Blank 1: potential Blank 2: current Blank 3: constant Blank 4: resistance

The unit of resistance is named for Georg Ohm because he discovered that the ratio of ____ difference to ____ is _____ for a given conductor, so this ratio can be defined as the _____ of the conductor.

Blank 1: equivalent Blank 2: resistance

The value of a single resistor that, when it replaces all the resistors in the circuit, results in the same current is the ____ _____ resistance of the circuit.

Blank 1: resistance Blank 2: ohm Blank 3: losses or loss

Thick transmission wires have very low ____ —a fifth of a(n) ____ per kilometer—because this helps reduce energy _____ during transmission.

I = ΔVsource/R

To find the current through a series circuit, first calculate the equivalent resistance and then use which equation?

Blank 1: ammeter Blank 2: series Blank 3: voltmeter Blank 4: parallel

To measure the current flowing through a device, a(n) ___ must be connected in ___ with the device. To measure the voltage across a device, a(n) ____ must be connected in ____ with the device.

True

True or false: A current of less than 1 A can be fatal.

False

True or false: A kilowatt-hour is a measure of power.

False

True or false: Given the current and resistance in a circuit, if you want to determine the thermal energy generated by the circuit in one minute, you must first find the power of the circuit.

The total current into a section of an electric circuit must equal the total current out of that same section.

What does the junction rule state?

a type of connection in which there are two or more current paths to follow

What is a parallel connection?

a material with zero resistance

What is a superconductor?

the direction in which a positive test charge moves

What is meant by conventional current?

the measure of how strongly an object or a material impedes current produced by a potential difference

What is resistance?

2.08 A

When a 25.0-V battery is connected to a 15.0-Ω resistor, what current flows in the circuit?

2.0 Ω

When two resistors are connected across a potential difference of 6.0 V, a current of 1.7 A flows. Given that the first resistance is 1.5 Ω, what is the second resistance?

dimmer switches analog joysticks control circuits for electric motors

Which devices make use of variable resistors?

electrical energy to thermal energy electrical energy to radiant energy

Which energy transformations occur in an incandescent light bulb?

R = ΔV/I

Which equation correctly relates current, potential difference, and resistance?

P = IΔV

Which equation correctly relates power, current, and potential difference?

ΔVsource = IR R = R1 + R2 + ... I = ΔVsource/R

Which equations are useful in solving problems involving equivalent resistance in series circuits?

E = I^2Rt E = Pt E = ((ΔV)2/R)(ΔV)2R t

Which equations give the electrical energy converted to thermal energy in a circuit that operates at constant power?

a kilowatt-hour

Which is an energy unit equal to 1000 watts delivered continuously for 3600 s (1 h), or 3.6 × 106 J?

any closed loop or conducting path allowing electric charges to flow

Which is the correct definition for an electric circuit?

Current through a material is directly proportional to the potential difference between its ends

Which is the correct statement of Ohm's law?

ampere (A)

Which is the correct term for a flow of electric charge equal to one coulomb per second (1 C/s)?

a device designed to have a specific resistance

Which is the definition of a resistor?

- higher voltage - shorter wires - thicker wires

Which measures help reduce Joule heating losses in electrical power transmissions?

zero thermal energy transformation zero potential difference zero resistance

Which properties do superconductors have?

- potential energy - charge - energy

Which quantities are conserved in a complete electric circuit?

the junction rule the loop rule

Which rules did Kirchhoff formulate?

Some electrical components obey Ohm's law, meaning they have constant resistance, at least over a certain range of voltages, but some do not.

Which statement accurately describes the resistances of electrical components?

Charge cannot be created or destroyed.

Which statement explains why current is the same in all parts of a series circuit?

Changing the resistance changes the current in inverse proportion. Changing the potential difference changes the current proportionally.

Which statements about controlling the current in a circuit are accurate?

- Electric current requires a potential difference. - The direction of conventional current is opposite to the direction of electron flow. - Any flow of charged particles is considered an electric current.

Which statements about electric current are accurate?

- Energy losses can be reduced by reducing either the current in the transmission wires, the resistance of the transmission wires, or both. - The total resistance of a transmission wire, and therefore the Joule heating loss, increases with the length of wire. - Energy is lost during electricity transmission in the form of thermal energy.

Which statements about energy losses during electricity transmission are accurate?

A connection with multiple paths is a parallel connection. Every circuit is either a parallel or a series connection.

Which statements about parallel and series connections are accurate?

Dry skin has a higher resistance than wet skin. The electrical resistance of skin is variable.

Which statements about the electrical resistance of human skin are correct?

The readings of the ammeters depend on the sum of the resistances. Each ammeter reads the same.

Which statements about the readings of the three ammeters in the circuit shown are accurate?

Use Kirchoff's junction rule to find the current through the fuse. Use I = P/ΔV to determine the current through each appliance.

Which steps are part of the process of determining whether a breaker on a parallel circuit will be tripped?

ohm

Which unit is used for the quantity that is the ratio of potential difference to current?

Flowing electrons bump into the resistor's atoms, increasing the atom's kinetic energy, and the total kinetic energy, or thermal energy, increases.

Why does current moving through a resistor increase its thermal energy?

Blank 1: Electrical Blank 2: thermal

____ energy is transformed according to the equation P = I2R, which is why electrical engineers sometimes call the unwanted ____ energy the I2R loss.

Blank 1: Power Blank 2: electrical Blank 3: thermal Blank 4: second

____ is the rate at which energy is transformed from one form to another, so in an immersion heater that operates at 2 kW, 2000 J of ____ energy are converted into ____ energy every ____

chemical energy to electric potential energy

battery

potential difference

change in elevation above sea level

I

current

I = q/t

definition of current

P = E/t

definition of power

refrigerator

electric potential energy to kinetic energy

heater

electric potential energy to thermal energy

battery

evaporation of water by solar energy, creating a cycle

generator

kinetic energy to electric potential energy

an electric circuit containing an electric motor but not a waterwheel in a waterfall

kinetic energy to potential energy

a waterwheel in a waterfall but not an electric circuit containing an electric motor

kinetic energy to sound energy

v

potential difference

a waterwheel in a waterfall and an electric circuit containing an electric motor

potential energy to kinetic energy

P

power

current

rate of water flow

E = qΔV

relation of energy and potential difference

resistance

rocks and other large obstacles

P = IΔV

substitute for charge

P = qΔV/t

substitute for energy