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IGCSE Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

What is the current in parallel circuits?

A
  • the total current flowing around the circuit is equal to the total of all currents through the separate component
  • in a paraelle circuit, there are junctions where the current splits or rejoins. the total current going into a junction has to equal the total current leaving
  • if two identical components are connected in parallel, then the same current will flow through each component
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2
Q

How does increasing the voltage work to distribute energy?

A
  • step-up transformer steps up the voltage, for efficient transmission and brings it down to safe, usable levels at the step-down transformer
  • voltage is increased using a step-up transformer
  • step-down transformers brings voltage down
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3
Q

Label the three wires on a plug

A

left: neutral wire (blue)
middle: earth wire (green and yellow)
right: live wire (brown)

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4
Q

Why do diodes rectify alternating current?

A
  • mains electricity supplies alternating current
  • many devices need direct current
  • a single diode only lets through current in half of the cycle
  • called half wave rectification
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5
Q

What is a light-dependent resistor?

A
  • a reistor dependent on the intensity of light
  • in bright light, resistance falls
  • in darkness, resistance is highest
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6
Q

What is charge?

A
  • the size of the electric current is the rate of flow of electric charge
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7
Q

What is a thermistor?

A
  • a temperature dependent resistor
  • in hot conditions, resistance drops
  • in cool condition, resistance increases
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8
Q

What is the blue wire?

A
  • the NEUTRAL wire

- is always at 0V

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9
Q

What are series circuits?

A
  • the different components are connected in a line, end to end between the positive and negative of the power supply
  • except voltmeters, but they’re not part of the circuit
  • if you rremove or disconnect one component, the circuit is broken and they all stop
  • not handy
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10
Q

What is the current in series circuits?

A
  • the same everywhere

- the size of current is determined by the total PD and the total resistance

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11
Q

What reading do you get on an oscilloscope trace for DC and AC?

A
  • DC: a straight line, due to same voltage

- AC: a repeating wave. you can work out the period and the frequency of the supply

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12
Q

What is the formula for energy transformed

A
  • energy transformed = charge x potential difference
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13
Q

Circuit Symbols

A

GO LEARN THEM NOW!

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14
Q

What happens if you increase the resistance of a variable resistor?

A
  • decreases the current flowing through the circuit
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15
Q

What is a diode?

A
  • a device made from a semiconductor material such as silicon
  • used to regulate the potential difference in circuits
  • lets the current flow freely thorugh it in one direction, but not in the other (very high resistance)
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16
Q

What is the equation for charge, current and time?

A
  • current (A) = charge (Q) / time (s)
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17
Q

What is the cell voltage in series circuits?

A
  • they add up
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18
Q

What is the formula for electrical power?

A
  • power = current x potential difference

- P = I x V

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19
Q

Learn the current-potential difference (I-V) graphs

A

LEARN THEM NOW!

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20
Q

What is the resistance in series circuits?

A
  • total resistance is the sum of all resistance

- the bigger the resistance of the component, the bigger its share of the total PD

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21
Q

What is current?

A
  • a flow of electric charge round a circuit
  • in amperes A
  • current will only flow through a component if there is a potential difference across that component
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22
Q

What does anything that supplies electricity also supply?

A
  • energy
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23
Q

how does the National Grid work?

A
  • takes electrical energy from the power stations to where its needed in homes and industry
  • it enable power to be generated anywhere on the grid and supplied anywhere else on the grid
24
Q

What current do cells and batteries supply?

A
  • DC

- current always flowing in the same direction

25
Q

What is the ammeter?

A
  • measure the current (in amps) flowing through the component
  • must be placed in series
  • can be put anywhwere in series in the main circuit but never parallel
26
Q

What is a kilowatt hour?

A
  • the amount of electrical energy used by a 1kW appliance left on for 1 hour
27
Q

How should fuses be rated?

A
  • rated as near as possible but

- just higher than the normal operating current

28
Q

What is the power of an appliance?

A
  • the rate at which it transfers energy
29
Q

What is the main reason why mains electricity is AC?

A
  • so that transformers work

- they only work on AC

30
Q

What are circuit breakers?

A
  • an electrical safety device used in some circuits
  • they protect the circuit from damage if too much current flows
  • when they detect a surge in current, they break the circuit by opening a switch
31
Q

Describe safety features in a three pin plug

A
  • cable grip tightly fastened over the cable outer layer
  • metals parts made of copper or brass as they are good conductors
  • case, gable grip and cable insulation made of rubber and plastic because good insulators and flexible
32
Q

Why does fuse rating increase?

A
  • the larger the current, the thicker the cable

- the thicker the cable, the larger the fuse

33
Q

What are the pros and cons of circuit breakers?

A
  • you can reset it easily by flicking a switch, so convenient
  • operates much faster
  • safer, no need to melt fuse
  • work for small current changes, so more effective than fuses
  • a lot more expensive
34
Q

What is the problem with a high current when distributing electricity?

A
  • you lose a lot of energy through heat in the cables

- cheaper to increase the voltage

35
Q

What is the voltmeter?

A
  • measures the potential difference (in volts) across the component
  • must be placed in parallel around the component
  • a voltmeter has a very high resistance so if you place it in series in the circuit, there will be almost no current able to flow
36
Q

What is the formula for resistance, potential difference and current?

A

potential difference (V) = current (I) x resistance (R)

37
Q

Describe the residual current circuit breaker (RCCB)

A
  • if live wire is touched, a small but deadly current will flow through them to the earth
  • this means the neutral wire carries less current than than live wire
  • RCCB detects this difference and cuts off power by opening a switch
38
Q

What is potential difference?

A
  • the driving force that pushes the current round
  • also called voltage V
  • it is the energy transferred per coulomb of charge that passes between two points in an electrical circuit
39
Q

What do resistors produce when current flows through them?

A
  • heat

- the more current that flows, the more heat is produced

40
Q

Give the equation for power rating

A
  • power (W) = energy transferred (in J) / time (s)
41
Q

What is the green and yellow wire?

A
  • the EARTH WIRE
  • protects the wiring and for safety
  • it works with a fuse to prevent fire and shocks
  • attached to the metal casing of the appliance and carries the electricity to earth if something goes wrong and the live and neutral wires touch the metal case
42
Q

What is the potential difference in parallel circuits?

A
  • all components get the full source of PD, so voltage is the same across all components
  • e.g. identical bulbs in parallel will be at the same brightness
43
Q

what is double insulation?

A
  • if an appliance has a plastic casing and no metal parts showing
  • so it doesnt need an earth wire
  • these are two-core cables
44
Q

Describe how earthing and fuses prevent electrical overloads

A
  • if a fault develops in which the live wire touches the metal case, then because the case is earthed, too great a current flows in through the live wire, through the case and out down the earth wire
  • this surge in current melts the fuse when the amount of current is greater than the fuse rating
  • this cuts off the live supply and breaks the circuit
  • this isolates the whole appliance, making it impossible to get an electric shock from the case also prevents risk of fire caused by heating effect
45
Q

What happens when resistor gets hot?

A
  • when an electrical charge flows through a resistor, some of the electrical energy is transferred to heat energy
  • resistor gets hot
  • this energy causes the ions in the resistor to vibrate more
  • its more difficult for the charge-carrying electrons to get through the resistor
  • current can’t flow as easily and resistance increases
46
Q

What is the formula for potential difference?

A
  • PD (V) = energy transferred (E) / Charge (Q)
47
Q

What is the potential difference in a series circuit?

A
  • the total PD is shared between various components

- the voltages round a series circuit always add up to the source voltage

48
Q

What happens to the charge when a bigger current flows?

A
  • a bigger charge
49
Q

What happens when an electrical charge foes through a charge in potential difference?

A
  • energy is transferred
50
Q

What are parallel circuits?

A
  • each component is separately connected to the positive and negative of the supply
  • if you remove or disconnect one, it will hardly affect others
51
Q

Descrive UK mains supply

A
  • AC supply, current constantly changing direction
  • approx 230 volts
  • frequency is 50 cycles per second (50 Hz)
52
Q

Which wires does electricity normally flow through?

A
  • neutral and live wire
53
Q

What is resistance?

A
  • anything in the circuit that slows the flow down

- in ohms

54
Q

What are light-emitting diodes?

A
  • an Led emits light when a current flows through it in the forward direction
  • used a lot in lighting as they used a much smaller current
55
Q

What is the brown wire?

A
  • the LIVE wire

- alternates between high positive and negative voltage

56
Q

The ______ the resistance of a component, the smaller the current that flows?

A
  • greater

IGCSE Physics (8 decks)

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