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Fundamentals of Physics > Chapter 23: Electric Current > Flashcards

Chapter 23: Electric Current Flashcards

1
Q

Electrons are made to flow in a wire when there is

A

a potential difference across its ends.

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2
Q

Which statement is correct: a) Charge flows in a closed circuit; b) Voltage flows through an open or a closed circuit; c) Resistance flows through an open circuit; d) Current is the primary cause of voltage.

A

a) Charge flows in a closed circuit.

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3
Q

Heat a copper wire and its electric resistance

A

increases.

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4
Q

In an ac circuit, the electric field: a) increases via the inverse-square law; b) changes magnitude and direction with time; c) is the same everywhere; d) none of these.

A

b) changes magnitude and direction with time.

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5
Q

A 10-ohm resistor has a 5-A current in it. What is the voltage across the resistor? a) 5V; b) 10V; c) 15V; d) 20V; e) more than 20V.

A

e) more than 20V.

V = IR = 5A * 10ohm = 50V

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6
Q

Modern automobile headlights are connected in

A

parallel.

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7
Q

The source of electrons lighting an incandescent ac light bulb is

A

atoms in the light bulb filament.

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8
Q

Electrons move in an electrical circuit by

A

interacting with an established electric field.

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9
Q

On some early automobiles both headlights went out when one bulb burned out. The headlights must have been connected in

A

series.

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10
Q

The current through a 10-ohm resistor connected to a 120-V power supply is

A

12A

I = V/R = 120V / 10ohm = 12A

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11
Q

A circuit breaker often serves the same purpose as a

A

fuse.

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12
Q

Stretch a copper wire so that it is thinner and the resistance between its ends

A

increases.

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13
Q

Alternating current is normally produced by a

A

generator.

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14
Q

When two lamps are connected in series to a battery, the electrical resistance that the battery senses is: a) more than the resistance of either lamp; b) less than the resistance of either lamp; c) none of these.

A

a) more than the resistance of either lamp.

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15
Q

A 100-Watt lamp glows brighter than a 25-Watt lamp. The electrical resistance of the 100-Watt lamp must be

A

less

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16
Q

The electric power of a lamp that carries 2 A at 120 V is

A

240 Watts.

P = I * V = 2A * 120V = 240W

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17
Q

In a common dc circuit, electrons move at speeds of: a) a fraction of a centimeter per second; b) many centimeters per second; c) the speed of light; d) none of these.

A

a) a fraction of a centimeter per second.

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18
Q

The difference in electrical potential between two points, measured in volts.

A

Potential difference;

When two points of different electric potential are connected by a conductor, charge flows so long as a potential difference exists. (Synonymous with voltage difference.)

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19
Q

The flow of electric charge that transports energy from one place to another.

A

Electric current;

Measured in amperes, where 1 A is the flow of 6.25 x 10^18 electrons per second, or 1 coulomb per second.

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20
Q

The property of a material that resists electric current.

A

Electrical resistance;

Measured in ohms.

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21
Q

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.

A

Ohm’s law;

Current = voltage / resistance; A potential difference of 1 V across a resistance of 1 ohm produces a current of 1 A.

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22
Q

Electrically charged particles flowing in one direction only.

A

Direct current (dc)

Electrons always move from the negative terminal toward the positive terminal.

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23
Q

Electrically charged particles that repeatedly reverse direction, vibrating about relatively fixed positions.

A

Alternating current (ac)

Electrons alternate to-and-fro about fixed positions. This is accomplished by alternating the polarity of voltage at the generator or other voltage source.​ In the U.S. the vibrational rate is commonly 60 Hz.

24
Q

The rate of energy transfer, or the rate of doing work; the amount of energy per unit time which electrically can be measured by the product of current and voltage.

A

Electric power;

Power = current x voltage or P = I*V; Electric power is measured in watts (or kilowatts), where 1 W = 1 A x 1 V = 1 J/s

25
Q

An electric circuit in which electrical devices are connected along a single wire such that the same electric current exists in all of them.

A

Series circuit;

In a series circuit, the total resistance to current is the sum of individual resistances. (∑R)

26
Q

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 the others.

A

Parallel circuit

27
Q

The flow of _______ is analogous to water flowing.

A

charge;

Charge flows from one end to the other (potential difference).

28
Q

Which of these statements is true: a) Electric current is a flow of electric charge; b) Electric current is stored in batteries; c) Both A and B are true; d) Neither A nor B are true.

A

a) Electric current is a flow of electric charge.

Voltage, not current, is stored in batteries. The voltage will produce a current in a connecting circuit. The battery moves electrons already in the wire, but not necessarily those in the battery.​

29
Q

In metal wires​: Conduction electrons are charge _______ that are free to move throughout atomic lattice.​

A

carriers

30
Q

In metal wires: Protons are bound within the

A

nuclei of atoms.

31
Q

When we flip the light switch on a wall and the circuit (an electric field) is established inside the conductor:​
The electrons continue their random motions while simultaneously being nudged by

A

the electric field.​

32
Q

When we flip the light switch on a wall and the circuit (an electric field) is established inside the conductor:​ ______ is established through the wires at nearly the speed of light. ​It is not the _______ that move at this speed.​ It is the _______ ______ that can travel through a circuit at nearly the speed of light.

A

1st blank: Current
2nd blank: electrons
3rd & 4th blank: electric field

33
Q

Electrons throughout the entire closed path of a circuit all react simultaneously to the

A

electric field.​

34
Q

Materials in which one or more of the electrons in the outer shell of its atoms are not anchored to the nuclei of particular atoms but are free to wander in the material?

A

Conductors; Metals such as copper and aluminum.

35
Q

Materials in which electrons are tightly bound and belong to particular atoms and are not free to wander about among other atoms in the material, making them flow​?

A

Insulators; such as rubber, glass. ​

​

36
Q

In regard to electric resistance, the higher the temperature, ​

A

the more the resistance​.

37
Q

Electric resistance is _______ proportional to cross-sectional area.

A

inversely;

This means thin wires have more resistance than thick wires.

38
Q

Electric resistance is _______ __________ to length.

A

directly proportional;

This means rubber has more resistance than​ copper of the same size.

39
Q

Our body’s resistance can range from ____ ohms to ______ ohms.

A

100 ohms to 500,000 ohms

40
Q

Germanium and silicon are examples of

A

semiconductors.

41
Q

Ceramic material(s) is an example of

A

superconductors.

Specifically high-temperature superconductors that can carry much current at low voltage.

42
Q

Resistors​ regulate ______ inside​ electrical devices.

A

current

43
Q

Chemical batteries​ are an example of

A

voltage sources.

They work by chemical disintegration of zinc or lead in acid.​

44
Q

Energy stored in chemical bonds is converted to

A

electric potential energy.

45
Q

When you double the voltage in a simple electric circuit, you double the​: a) current; b) resistance; c) both A and B; d) neither A nor B.

A

a) current

Power transmission is more efficient at higher voltages (220 V versus 120 V).

46
Q

For a constant resistance (R), current will be twice (2I) as much for

A

twice the voltage (2V).​

47
Q

For twice the resistance (2R) and twice the voltage (2V), current (I) will be

A

unchanged.

48
Q

When a bird is perched on a single wire, its two feet are at the same

A

electrical potential.

Therefore, the electrons in the wires have no motivation to travel through the bird’s body.​ If the bird touches a second wire it will open a path for the electrons to go through the bird’s body. ​

49
Q

When converting ac to dc, what is the tiny electronic device that acts as a one-way valve to allow electron flow in one direction only​?

A

a diode;

When input to a diode is ac, output is pulsating dc.

50
Q

Slow charging and discharging of a ________ provides continuous and smoother current.

A

capacitor

51
Q

A pair of ______ is used so there are no gaps in current output. The pair reverses the polarity of alternate half-cycles instead of eliminating them.​

A

diodes

52
Q

Household current is ___, but the current in a laptop is ___.

A

1st blank: ac

2nd blank: dc

53
Q

When you plug a lamp into an outlet, ______ flows from the outlet into the lamp, not electrons.

A

energy;

Electrical utility companies sell energy. You provide the electrons.

54
Q

______ is carried by the pulsating electric field and causes vibratory motion.​

A

Energy

55
Q

LED stands for

A

light-emitting diode

56
Q

Consider a lamp powered by a battery. Charge flows​: a) out of the battery and into the lamp; b) from the negative terminal to the positive terminal; c) ​with a slight time delay after closing the switch; d) through both the battery and the lamp.

A

d) through both the battery and the lamp.

Remember, charge is already in all parts of the conducting circuit. The battery simply gets the charges moving. As much charge flows in the battery as outside. Therefore, charge flows through the entire circuit.

57
Q

When two identical lamps in a circuit are connected in parallel, the total resistance is​: a) less than the resistance of either lamp; b) ​the same as the resistance of each lamp; c) less than the resistance of each lamp; d) none of the above.

A

a) less than the resistance of either lamp.

Resistors in parallel are like extra lines at a checkout counter. More lines means less resistance, allowing for more flow.​

Fundamentals of Physics (24 decks)

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