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GCSE Physics > P1 Electricity > Flashcards

P1 Electricity Flashcards

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1
Q

Define electrical current

A
  • flow of electrical charge (electrons)

- higher flow = higher current

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2
Q

How is an ammeter connected to a circuit? What does it measure?

How is a voltmeter connected to a circuit? What does it measure?

A
  • Ammeters measure current, connected in series

- Voltmeters measure voltage, connected in parallel

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3
Q

How does resistance effect?

  • flow of charge
  • current
A
  • more difficult for charge to flow

- so current is lower

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4
Q

Define potential difference

A

The difference in electrical potential between two points in a circuit, like and electrical “push”

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5
Q

How does increasing potential difference effect

  • flow of change
  • current t
A
  • greater flow of charge through component

- bigger current

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6
Q

In a V-I graph, what does the gradient show?

A
  • Resistance
  • steep gradient = low resistance (large current will flow for a small pd)
  • shallow gradient = high resistance (large of needed to produce a small current)
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7
Q

What does the graph for a resistor look like? What does this indicate?

A
  • For resistors e.g. Ohmic Conductors
  • current is directly proportional to potential difference (at a constant temperature), linear graph, resistance is constant as current changes
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8
Q

What does the graph for a filament lamp look like? What does this indicate?

A
  • current through a filament lamp increases -> temperature increases
  • so resistance increases as current does so graph is curved
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9
Q

What does the graph for a diode look like? What does this indicate?

A
  • current only flows in one direction
  • high resistance in curved direction
  • horizontal line when no current flows
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10
Q

How does resistance effect temperature in a thermistor? What is this useful for?

A
  • resistance decreases as temperature decreases

- good for temperature control and response (e.g. thermostat that turns on at a specific temperature)

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11
Q

How does resistance effect light in a LDR? What is this useful for?

A
  • resistance decreases as light intensity increases

- useful for automatic lights (e.g. dusk til dawn lights)

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12
Q

In a series circuit, what happens to current around the circuit?

A

It is the same through each component

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13
Q

In a parallel circuit, what happens to current around the circuit?

A

The current drawn from the power supply is split between each component. Adding them all up = current from power supply

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14
Q

In a series circuit, what happens to potential difference around the circuit?

A

Shared between components

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15
Q

In a parallel circuit, what happens to potential difference around the circuit?

A

It is the same across each component

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16
Q

What happens to resistance in a series circuit?

A
  • Total resistance of two components is the sum of resistance of each component
  • R1 + R2 = Rtotal
  • Adding components in series increases resistance
17
Q

How is resistance effected in a parallel circuit?

A
  • Total resistance of two resistors is less than the smallest individual resistor
  • In parallel, there are more paths for current to take, so current flows more easily
  • So adding resistors in parallel decreases total resistance
18
Q

What does power in a circuit depend on?

A
  • potential difference and current ( P=VI)

- higher pd or current will use more energy/second than lower pd or current, which means it is more powerful

19
Q

Describe direct current

in terms of potential difference, current and display on an oscilloscope

A
  • PD is always positive or always negative
  • Current direction is always the same
  • Supplied by cells and batteries
  • Straight line on an oscilloscope
20
Q

Describe alternating current

in terms of potential difference, current and display on an oscilloscope

A
  • PD alternated between positive and negative
  • Current direction changes
  • Used in mains electricity
  • Wave/alternating on an oscilloscope
21
Q

What is the potential difference and frequency of mains electricity?

A
  • 230V

- AC - changes direction 50 times a second = 50Hz

22
Q

Describe a three-core cable (voltage, colour etc)

A
  • live wire, brown, 230V - carries current to appliance
  • neutral wire, blue, (close to) 0V earth potential - carries current away from appliance
  • earth wire, yellow/green stripes, 0V
23
Q

What happens in a three core cable during operation?

A
  • PD causes current to flow through live and neutral wires
  • Live wire carries alternating potential from supply
  • Neutral wire completes the circuit
  • Current will only flow in earth wire if there is a fault connecting it to a non 0 potential (live wire)
  • Earth wire is for safety to stop exterior of appliance becoming live
24
Q

Why is touching a live wire dangerous?

A
  • Our bodies are 0v
  • creates a large pd across the body
  • large current flows through body
  • can be fatal
25
Q

Why is it dangerous if a tv is switch if but still plugged in and switched on at the wall?

A
  • live wire ire between the wall and switch is still at an alternating potential
  • Just needs a path for the electricity to flow through
  • Path could be provided by a damaged cable exposing the live wire
  • If someone touches the live wires creating a pd from the live to the earth causing the current to flow -> electric shock
26
Q

1J of energy transfer =

A

1W of power

27
Q

How can you increase efficiency?

A

Reduces wasted energy transfers

28
Q

Define power

A

Rate at which energy is transferred

29
Q

What happens when charge flows and has to overcome resistance in a circuit?

A
  • work is done depending on amount of charge that flows and potential difference
30
Q

Explain how the National Grid works

A

Power Station

  • 25000V
  • transfer energy supply in to electrical energy
  • more efficient than many local power stations as they are more efficient (steam turbines are more efficient at higher steam temperatures)

Step up transformers

  • Increase Pd
  • Reduces current so reduces heat loss so more efficient

Transmission cables
- transfer electricity

Step down transformers
- reduces pd for domestic use (230V)

31
Q

How is static electricity produced?

A
  • Insulators rubbed together
  • friction moves negative electrons between the objects
  • gain electrons - negative charge
  • loose elections - positive charge
  • insulators means charge remains and builds up
32
Q

What does it mean for an object to be isolated?

A

No conducting path to earth

33
Q

How is an electrical charge produced?

A
  • As charge on an isolated object increases, potential difference between object and earth increases
  • Potential difference becomes too high
  • Spark jumps across the gap to any earthed conductor nearby
  • Spark discharges the object and can be a source of ignition
  • Lightning = charge build up in clouds in a thunderstorm producing a spark
34
Q

What type of force is an electrostatic force?

A
  • non contact (attraction or repulsion
  • if a charge object is brought near an uncharged object, it can attract it (e.g charged ruler near water flowing from a tap)
35
Q

What does the strength of an electric field depend on?

A
  • distance from the object (further distance = weaker field)

- amount of charge ( higher charge = stronger field )

36
Q

How can field lines show electrostatic forces?

A
  • Pointing away = positive
  • Pointing towards centre = negative
  • Arrow direction = direction of positive charge (opposites attract)
  • Closer lines = stronger field
37
Q

Describe the resistance required practical

A
  • how does length of wire effect resistance?
  • record voltage and current at varying lengths (use crocodile clips to grip at certain points)
  • calculate resistance (r=v/i)
  • use a variable resistor to control current
  • only turn current on when taking a reading
38
Q

Describe the V-I characteristics practical

A
  • use variable resistor to adjust PD across component
  • measure voltage and current for a range of voltages
  • calculus a mean
  • measure with power supply off to check for 0 errors

GCSE Physics (11 decks)

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