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Physics 2 > Unit 4 (lesson 14-15) > Flashcards

Unit 4 (lesson 14-15) Flashcards

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1
Q

what is necessary for the flow of charge?

A

difference in electric potentials between both ends.

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2
Q

what is meant by the term potential

A

voltage

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3
Q

does a charge flow through circuit or into a circuit

A

Through

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4
Q

does voltage flow through a circuit or is voltage established across a circuit

A

voltage established across a circuit

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5
Q

is electric resistance greater in a short fat wire or a long thin wire

A

Greater in a long, thin wire

-thick wires have less resistance than thin wires. longer wires have more resistance than short wires.

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6
Q

how does wetness affect the resistance of your body

A

water conducts current to humans. Ions in ordinary water greatly reduce electric resistance.

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7
Q

why is it that a bird can perch without harm on a high-voltage wire

A

For a bird to perceive shock, there must be a difference in potential between one part of the bird’s body and another part

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8
Q

what is a typical “drift” speed of electrons that make up a current in a typical DC circuit

A

0.01cm/s

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9
Q

what is a typical “drift” speed of electrons that make up a current in a typical AC circuit

A

0 since direction of current alternates.

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10
Q

from where do the electrons originate that flow in a typical electric circuit

A

in the conducting circuit material itself

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11
Q

definition and unit for current

A

current = flow of charge = Ampere

  • SI unit that measures electric current.
  • symbol A
  • flow of 1 coulomb of charge/second
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12
Q

definition and unit for voltage

A

voltage = electric “pressure” or potential energy per charge = Volt

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13
Q

definition and unit for resistance

A

resistance = electric “friction” that works against flow = ohms

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14
Q

Where do the electrons come from in a circuit?

A

When voltage is applied to a wire, the electrons from the metal of the wire itself move.

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15
Q

how is electric power related to current and voltage

A

Power is directly related to both current and voltage, so power is greater when current is greater and when voltage is greater.

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16
Q

Explain how the electricity produced by a battery is different from the electricity that comes from a wall socket.

A
  • Batteries produce direct current which flows in only one direction
  • the wall socket is powered from the “grid” which provides alternating current that oscillates back and forth 60 times each second.
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17
Q

equation for power

A

Power (P) = Current (I) x Voltage (V).

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18
Q

Why does a light bulb glow more brightly when more current is passed through it?

A
  • As current increases, resistance increases which increases heat.
  • As the temperature of an object increases it emits light at higher and higher frequencies.
  • The wire is glowing-hot due to the friction of the moving charges.
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19
Q

3 basic components in a circuit

A

a voltage source, a resistor, and wires.

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20
Q

Two rules to follow when adding resistors

A

1: When adding resistors in series—Total resistance = R1 + R2 +…
2: When adding resistors in parallel—1/Total resistance = 1/R1 + 1/R2 + …

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21
Q

circuit

A

complete path

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22
Q

in a flashlight, when the switch is turned on to complete an electric circuit, the mobile conduction electrons…

A

already in the wires and the filament begin to drift through the circuit

23
Q

any path along which electrons flow is…

A

a circuit

24
Q

what must there be for a continuous flow of electrons

A

a complete circuit with no gaps. a break in an electric circuit results in a complete stop in the flow of electricity

25
Q

series circuit

A

devices in a circuit form a single pathway for electron flow between terminals of the battery, generator, or wall socket

26
Q

important characteristics of series connections

A
  1. electric current has single pathway through the circuit. current passing through each electric device is the same
  2. this current is resisted by the resistance of the first and any other devices, so that the total resistance to current in the circuit is the sum of the individual resistances along the circuit path
  3. the current in the circuit is numerically equal to the voltage supplied by the source divided by the total resistance of the circuit. Ohm’s Law
  4. Ohm’s law applies separately to each device.
  5. The total voltage impressed across a series circuit divides among the individual electric devices in the circuit so that the sum of all voltage drops across the individual devices is equal to the total voltage supplied by the source.
27
Q

main disadvantage of a series circuit

A

if one device fails in a series circuit, current in the whole circuit ceases and none of the devices will work.

28
Q

parallel circuit

A

devices in a circuit form branches, each of which is a separate path for the flow of electrons

29
Q

In a parallel circuit, each device operates…

A

independent of the other devices. A break in any one path does not interrupt the flow of charge in the other paths.

30
Q

major characteristics of parallel connections

A
  1. each device connects the same to points A and B of the circuit
  2. the total current in the circuit divides among parallel branches
  3. the total current in the circuit equals the sum of the currents in its parallel branches
  4. as the number of parallel branches is increased, the total current through the battery increases.
31
Q

schematic diagrams

A

simple diagrams that describe electric circuits

32
Q

In a schematic diagram…

A
  • resistance is shown by a zigzag line
  • ideal resistance-free wires are shown with solid straight lines
  • A battery is represented with a set of short and long parallel lines
33
Q

the equivalent resistance of resistors connected in a series is the…

A

sum of their values

34
Q

the equivalent resistance for a pair of equal resistors in parallel is…

A

half the value of either resistor

35
Q

to prevent overloading in circuits, fuses or circuit breakers are…

A

connected in series along the supply line.

36
Q

how do you add resistors when they are in series?

A

The total resistance = sum of the individual resistors.

37
Q

how do you add resistors in parallel

A

The inverse of the total = sum of the inverse of each individual resistor.

38
Q

what is “overloading”

A

Wires that are carrying more current than is safe are “overloaded.”

39
Q

what are the possible results of “overloading”

A

they may overheat, melt the insulation around them, and cause fires.

40
Q

what does a circuit breaker do when wires are overloaded

A

when wires are overheating, the circuit breaker gets tripped—which breaks the circuit and stops the flow of electricity until it is manually reset.

41
Q

are all the electrons flowing in a circuit provided by the battery?

A

No, the battery, circuit, switch, and even the resistor, all contribute electrons.

42
Q

If three bulbs are connected in series to a 6V battery, how many volts are there across any individual lamp?

A

While the entire current passes through each lamp, each lamp has a potential difference of only 2V across it.

43
Q

What happens to a series circuit with 3 bulbs if one of them is broken?

A

If even one of the bulbs is broken, the current cannot flow through it and the whole circuit is broken.

44
Q

What is the total resistance of a circuit with 3 heaters of 15 ohms each, connected in series?

A

The total resistance = R1 + R2 +R3 = 15 +15 +15 = 45 ohms.

45
Q

What is the total resistance of a circuit with 3 heaters of 15 ohms each, connected in parallel?

A

1/Rtotal = 1/R1 + 1/R2 + 1/R3 = 1/15 +1/15 +1/15 = 0.067 + 0.067 + 0.067. 1/Rtotal = 0.201. Rtotal = 1/0.201 = 4.98 ohms.

46
Q

Calculate the current in a circuit powered by a 12 V battery and used to light a series of three 30 ohm resistors connected in series.

A

V = IR, so I = V/R = V/(30 +30 +30) = 12/90 = 0.13 A.

47
Q

Calculate the current in a circuit powered by a 12 V battery and used to light a series of three 30 ohm resistors connected in parallel.

A

V = IR, so I = V/R. 1/Rtotal = (1/30 + 1/30 + 1/30) = 3/30 = 0.1; Rtotal = 1/0.1 = 10 ohms; I = 12/10 = 1.2 A.

48
Q

Explain why the current is higher when the resistors are in parallel than when they are in series.

A

Resistors in parallel have a lower “equivalent” resistance. Because I = V/R, when R is decreased, current increases (assuming voltage stays constant).

49
Q

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

A

It grounds the case to zero potential.

50
Q

power

A

is the rate of doing work, the amount of energy transferred per unit time

51
Q

What is the equivalent resistance of a pair of 8-ohm resistors in series?

A

The equivalent resistance of a pair of 8-ohm resistors in series is 16 ohms.

52
Q

What is the equivalent resistance of a pair of 8-ohm resistors in parallel?

A

The equivalent resistance of a pair of 8-ohm resistors in parallel is 4 ohms.

53
Q

configuration of a working circuit

A

bulb filament that runs from the positive terminal to the negative terminal. Electrons flow from the negative terminal

54
Q

why does the total circuit resistance decrease when more devices are added to a parallel circuit

A

more pathways leads to the lowering of the combined resistance of the circuit which leads to a greater amount of current in the lines.

Physics 2 (7 decks)

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