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Physics > Electric Circuits > Flashcards

Electric Circuits Flashcards

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1
Q

what is the purpose of a switch?

A

to turn a circuit on (closed) or off (open)

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2
Q

how does a lamp work?

A

an electrical filament heats the filament inside a bulb so that it gives out light

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3
Q

what is a resistor?

A

it restricts or limits the flow of electrical current. a fixed resistor has a resistance that doesn’t change while a variable resistor’s resistance can be changed by moving a slider on the resistor

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4
Q

what is a thermistor?

A

it has a resistance that changes based on temperature - the colder it is, the higher the resistance

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5
Q

what is an LDR?

A

Light Dependent Resistor - resistance changes depending on light intensity - the lower the light intensity, the higher the resistance

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6
Q

what is the purpose of a semiconductor diode?

A

it allows current to flow in one direction only

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7
Q

what does a voltmeter do?
how do you connect it to a circuit?

A
  • it measures potential difference
  • you connect it in parallel (across the component)
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8
Q

what does an ammeter do?
how do you connect it to a circuit?

A
  • it measures current
  • you connect it in series (in line with the component)
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9
Q

how do you know if a circuit is complete?

A

if you can follow a wire from one end of the power supply, through the components, to the other end of the power supply, it is complete

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10
Q

what are the 2 types of current and describe them

A
  • direct current - electrons flows in one direction only
  • alternating current - direction of electron flow continually reverses
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11
Q

what is an electron?

A

it is a negatively charged particle that transfers energy through a wire as electricity

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12
Q

what is charge?

A

it is a property of certain objects like electrons and protons - they experience a force when in electric fields

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13
Q

how is charge measured?
bonus: how many electrons are in each of these?

A
  • coulombs
  • 1 coulomb = 6.25 x 10^18 electrons
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14
Q

what is current?

A

the rate of flow of electric charge

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15
Q

in what direction does current flow in an electric circuit?

A

it flows from positive to negative

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16
Q

what is the formula to calculate the amount of charge passing a point in the circuit?

A

charge = current x time
Q = It

Q = C
I = A
t = s

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17
Q

in a series circuit, current…

A

…is the same everywhere

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18
Q

how would you describe one amp?

A

the current that flows when one coulomb of charge passes a point in the circuit in one second

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19
Q

what 2 things does the current flowing through a component depend on?

A
  • resistance of the component
  • potential difference across the component
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20
Q

current will only flow through a circuit if there is…

A

…potential difference

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21
Q

what is potential difference?

A

it measures the amount of energy transferred per unit of charge

22
Q

what is the unit of potential difference?

A

Volts (V)

23
Q

1 V = ?

A

1 Joule per Coulomb

24
Q

what is the formula to calculate potential difference?

A

potential difference = energy / charge
V = E/Q

V = V
E = J
Q = C

25
Q

what is resistance?

A

anything in the circuit which reduces the flow of current

26
Q

what is resistance measured in?

A

ohms (Ω)

27
Q

the larger the resistance…

A

…the smaller the current

28
Q

what is the formula linking resistance, potential difference and current?

A

potential difference = current x resistance
V = IR

V = V
I = A
R = Ω

29
Q

what are the relative resistances of conductors and insulators?

A
  • conductors = low resistance
  • insulators = high resistance
30
Q

what is an ohmic conductor?

A

a device that obeys Ohm’s Law like wires or resistors

31
Q

what is Ohm’s Law?

A

current and potential difference are directly proportional

32
Q

as temperature of the filament in a filament bulb increases…

A

…resistance of the filament increases

33
Q

why do diodes not let current flow in the opposite direction?

A

it has a very high resistance in the reverse direction

34
Q

what are some components that are not ohmic conductors?
how do their resistances change?

A
  • lamps, diodes, thermistors and LDRs
  • resistance changes with current flowing through the component
35
Q

what are the uses of thermistors?

A
  • thermostats - resistance varies with temperature so you can detect temperature of the thermistor and the surroundings - can be used in a car engine to prevent overheating
36
Q

what are the uses of LDRs?

A
  • automatic night lights/outdoor lights - light levels fall, resistance of the LDR increases which triggers the light to turn on
  • burglar detectors - light is shone down. If the burglar steps in front of it and breaks the light beam, resistance of LDR shoots up and triggers an alarm
37
Q

what are the 2 ways you can set up a circuit?

A
  • in series
  • in parallel
38
Q

how does current flow in a series circuit?

A

current is the same everywhere

I1 = I2 = I3 …

39
Q

what would happen if one bulb blew out in a series circuit?

A

current wouldn’t be able to flow around the circuit - the circuit would be broken

40
Q

how does pd work in a series circuit?

A
  • energy is transferred from the power supply and is shared all across the circuit
  • total pd = sum of all pds across all components
  • total V = V1 + V2…
41
Q

how does resistance work in a series circuit?

A
  • current has to flow through all the resistors so pd is shared across all of them
  • total resistance is all the resistances added together
  • total R = R1 + R2 …
42
Q

what happens if a component breaks in a parallel circuit?

A

not much - only components on that branch would be affected. The other branches are independent of each other

43
Q

how does current work in parallel circuits?

A
  • current splits as it leaves the cell and goes into one of the loops
  • total current is the currents of each branch added together
  • total I = I2 + I3 + I4 …
44
Q

how does pd work in parallel circuits?

A
  • each branch gets the same pd as the source so pd is the same across all components
  • total V = V1 + V2 + V3 …
45
Q

how does resistance work in parallel circuits?

A
  • imagine 2 resistors are connected in parallel
  • both resistors have the same pd across them
  • but becuase of the extra branch, current has more than one path to go through
  • more total current can flow through the circuit
  • using V = IR, an increase in current means a decrease in the total resistance of a circuit
46
Q

is it possible to have components connected in series and in parallel in the same circuit?

A

yes

47
Q

which is more commonly used in actual things: parallel circuits or series circuits?

A

parallel circuits - everything can be turned on and off separately

48
Q

what is the formula for power in electric circuits?

A

power = current x potential difference OR power = current^2 x resistance
P = IV or P = I^2R

P = W
I = A
V = V
R = Ω

49
Q

how is energy transferred in electric circuits?

A
  • as electrons flow through wires, they collide with ions in the wire, causing the ions to vibrate more
  • increased ion vibration = increased wire temperature
  • energy is transferred: chemical energy store of battery -> internal energy store of wire
50
Q

1W = ?

A

1J/s

51
Q

what 2 ways can electric power be transferred?

A
  • low current with high voltage
  • high current with low voltage
52
Q

what is the most efficient way of transmitting electricity and why?

A
  • at a high voltage with a low current - wires stay cooler
  • high current has a higher heating effect on the wires so more energy is lost as heat energy

Physics (9 decks)

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