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Physics- Electricity > Electricity > Flashcards

Electricity Flashcards

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1
Q

What happens in direct current

A

The flow of electrons are consistently in one direction around the circuit

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2
Q

What happens in alternating current

A

The direction of electron flow continually reverses

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3
Q

What is electrical current

A

A flow of electrons

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4
Q

How do you measure current

A

With an ammeter that must be placed in series with that component

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5
Q

How to measure p.d

A

With a voltmeter that must be placed in parallel with that component

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6
Q

What do conductors and insulators have

A
  • conductors has a low resistance

- insulators have a high resistance

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7
Q

What is the iv characteristics for components

A

The relationship between current through and voltage across a component

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8
Q

What is the voltage in a fixed resistor (resistor at a constant temp)

A

The voltage is directly proportional to the current

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9
Q

What is ohms law

A

The rule that states that the current flowing through a resistor is directly proportional to the voltage across the resistor, provided the temp remains constant

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10
Q

What does directly proportional mean

A

If one quantity goes up by a certain percentage/ number, the other quantity goes up by the same percentage/ quantity as well

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11
Q

What would doubling the amount of energy into the resistor result in

A

A current twice as fast as the resistor

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12
Q

How do you know if the relationship is ohms law

A

Because the resistance of the resistor is fixed (because the temp doesn’t change)

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13
Q

What is a resistor…

A

An ohmic conductor

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14
Q

What would a graph plotting p.d against current for a fixed resistor look like

A

Diagonal straight across (because it is directly proportional)

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15
Q

What happens to the current in a filament bulb

A
  • The current doesn’t increase at the same rate as the voltage
  • doubling the amount of energy doesn’t cause a current twice as fast
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16
Q

What happens if you put more energy into the bulb of a filament lamp

A

The harder it is for the current to flow (resistance of the bulb increases)

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17
Q

What happens when the voltage increases in a filament lamp

A

The temp of the thin wires inside the bulb also increase

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18
Q

What happens in result of the temp being increased in a filament bulb

A
  • the increased vibrations of the ions in the filament make it harder for the electrons to get past
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19
Q

What does a graph plotting p.d against current for a filament bulb look like

A
  • Looks like an f

- The line is an upward curve that levels out and starts to dip as p.d increases

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20
Q

What does a semiconductor diode do

A

Only allows current to flow in one direction

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21
Q

What is the resistance of the diode like

A

Very large meaning no current would flow if the p.d was arranged to try and push current the wrong way

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22
Q

What does a graph plotting p.d against diode look like

A
  • line is horizontal on the x axis then curves upwards sharply
23
Q

What is the relationship in the resistance in a thermistor

A
  • the resistance of a thermistor varies w temp

- when the temp increases the resistance decreases

24
Q

What is the relationship of the resistance of an LDR

A
  • the resistance of an LDR varies with light intensity

- the more light on the LDR the smaller the resistance of it

25
Q

What happens in series circuits

A

Electrical components are connected one after another in a single loop

26
Q

What are the rules in a series circuit

A
  • electrons with pass through every component on its way round the circuit
  • if one bulb is broken then the current won’t flow round
  • if one bulb goes out they all go out
27
Q

Current in series

A
  • a series circuit is one loop

- all electrons in the loop form one current

28
Q

Explain how the resistance of a filament lamp changes as the p.d across it increases

A
  • the pd increases which increases current flow
  • this heats wire
  • through heat, the current gains more energy causing it to vibrate more
  • this lets fewer electrons through and causes a greater resistance
29
Q

If light intensity decreases what happens to the pd and current

A
  • pd increases

- current decreases

30
Q

What is pd

A

A measure of the energy given to the charge carries in a circuit

31
Q

What happens to pd in series circuits

A
  • the pd difference supplied is equal to the total of the pd across other components
32
Q

Resistance in series

A

If resistors are connected in series, the current flows through both of them meaning the resistances are added together

33
Q

Key points in series circuits

A
  • the current is the same through each component
  • the total pd difference of the power supply is shared between the components
  • the total resistance of the circuit is the sum of individual resistors
34
Q

What is the energy transferred each second equation

A

P = I x V or P = I squared R

35
Q

What do fuses do

A
  • breaks the circuit if an appliance causes too much current to flow
  • this protects the wiring and the appliance if something goes wrong
36
Q

How does a fuse protect electrical circuits and appliances

A
  • fuse contains a piece of wire that melts easily

- I’d current going through fuse is too great, wire heats up until it melts and breaks the circuit

37
Q

What are the standard fuse ratings

A
  • 3A
  • 5A
  • 13A
  • if the device works at 3A, use a 5A fuse
  • if the device works at 10A, use a 13A fuse
38
Q

Why are copper wires used in a plug

A

They are good conductors

39
Q

Why is a plastic coating used in wires

A

Plastic is a good insulator

40
Q

What does the live wire do

A

Carries the current that enters the device

41
Q

What does the neutral wire do

A

0V, completely safe, connects to cable in wall and completes the circuit

42
Q

What does earth wire do

A
  • if there is a fault, the earth wire carries away dangerous currents
  • low resistance path to ground
43
Q

What is the equation that links joules watts and power

A

E= p x t

44
Q

What does the national grid do

A
  • It distributes electricity across the country

- the electricity is produced by a power station turning a generator

45
Q

What are transformers used for

A
  • to change voltages and currents in transmission lines
46
Q

How do you determine whether the transformers will step up or down the voltage

A

The number of coils

47
Q

What does increasing voltage do in terms of transformers

A

Decreases current

48
Q

What does decreasing voltage do in terms of transformers

A

Increases current

49
Q

What does a step up transformer do and why

A

Increases voltage and reduces current

- less current so that less energy is lost through heating the wire

50
Q

What does a step down transformer do

A

Reduces the voltage to a safer voltage (230V) for home use

51
Q

What is the equation that links power current and resistance

A

P = I squared x R

52
Q

How to ensure minimum amount of power is lost from cables (national grid topic)

A
  • they are thick so resistance is low

- high voltages used to reduce current through the transmission lines

53
Q

Advantages and disadvantages of transformers

A

Physics- Electricity (3 decks)

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