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Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

Current

A

The rate of flow of electrical charge

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2
Q

What does current depend on

A
  • resistance -> greater the resistance the smaller the current
  • potential difference -> greater the pd the greater the current
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3
Q

Explain the current in an ohmic conductor

A

It is directly proportional to the potential difference across the resistor

-> this means that / is because of the resistance remains constant as the current changes

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4
Q

What happens to the resistance in a filament lamp

A

It increases as the temperature increases

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5
Q

Describe the current and resistance in a diode

A
  • the current only flows in one direction
  • it has very high resistance in the reverse direction
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6
Q

What happens to the resistance of a thermistor when temperature increses

A

It decreases

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7
Q

What happens to the resistance of an LDR when light instensity increases

A

It decreases

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8
Q

Application of thermistors

A

It is a temperature sensor regularly used as a thermostat -> this means it automatically regulates temperature or active a device when the temperature reaches a certain point

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9
Q

State Ohm’s law

A

The current through a conductor is directly proportional to the potential difference across it as long as temperature is constant

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10
Q

For components in a series circuit:

A
  • there is the same current through each component
  • the total pd of the power supply is shared between the components
  • the total resistance of 2 components is the sum of the resistance of each component
    -> R(total) = R1 + R2
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11
Q

For components connected in a parallel circuit:

A
  • the pd across each component is the same
  • the total current through the whole circuit is the sum of the currents through the separate components
  • the total resistance of 2 resistors is less than the resistance of the smallest individual resistor
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12
Q

Why does adding resistors in series increase resistance

A

Because the current is the same in every component, so the more resistors we add, the harder it is for current to flow and overall resistance increases

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13
Q

Why does adding resistors in parallel decrease resistance

A

The more resistors we add the more pathways the current has to go through so it is easier for current to flow, decreasing resistance

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14
Q

Frequency of UK mains supply

A

50Hz

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15
Q

Voltage of UK mains supply

A

230V

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16
Q

Difference between direct and alternating potential difference

A

Direct produced a constant electric current that flows in one direction, whilst alternating produces an alternating current that changes direction regularly

17
Q

How are appliances connected to the mains

A

Using a three-core cable

18
Q

Name the different wires’ colours

A

Live wire - brown
Neutral wire - blue
Earth wire - green and yellow stripes

19
Q

Role of the live wire

A

Carries the alternating potential difference from the supply

20
Q

Role of the neutral wire

A

Completes the circuit

21
Q

Role of the earth wire

A

Stops the appliance becoming live

22
Q

The dangers of providing connection between the live and earth wires

A

It would make a complete circuit from the mains supply to the ground and a shock or fire would likely occur

23
Q

Why is a live wire dangerous even if the switch is open (ie circuit is switched off)

A

Because touching it can complete the circuit between the live wire and the earth (as you’re standing on the floor) causing a shock

24
Q

Explain the relationship of power with current and pd

A

If current or pd increases the power increases (ie the rate of energy transfer increases)

25
Q

National Grid

A

A system of cables and transformers linking power stations to consumers

26
Q

Step-up transformers

A

Used to increase the pd so that current decrease and resistance also decreases in the wires reducing the energy lost to the surroundings

27
Q

Step down transformers

A

Decrease voltage so that it is safe to use in homes

28
Q

Static charge

A
  • when certain insulating materials are rubbed against each other they become electrically charged
  • negatively charged electrons are rubbed off one material and on to the other -> the material that gains electrons becomes negatively charged and the material that loses electrons has a positive charge
29
Q

Explain how sparks occur

A
  • when 2 objects have a strong electric field between them, electrons in the air molecules will be strongly attracted to the positively charged object
  • if the electric field is strong enough, electrons will be pulled away from the air molecules and cause a flow of electrons between the 2 objects -> this is a spark
30
Q

Explain the concept of an electric field

A

Area surrounding an electric charge that may influence other charged particles

31
Q

How does the concept of an electric field help explain the non-contact force between charged objects

A

The objects don’t need to touch, but do need to be within each others electric fields

32
Q

Where are the ammeter and voltmeter placed in relation to a circuit

A

Ammeter is in series with the circuit
Voltmeter is in parallel

33
Q

How does a thermostat reduce temp

A

if it gets too hot, the thermistor will have lower resistance, allowing more current to flow to potentially cool the room

34
Q

What is a resistor

A

an electrical component that is used to control the flow of electric current in a circuit

35
Q

How does a resistor work

A

by converting electrical energy into heat energy, which reduces the flow of current in a circuit

36
Q

What factors affect resistance

A
  • length of wire ->
  • thickness
  • material
  • temp
37
Q

Potential difference

A

energy transferred ,per unit of charge, between two points in a circuit

38
Q

Resistance

A

opposition to the flow of current

Physics (10 decks)

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