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Electricity Flashcards

(66 cards)

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1
Q

Dangers of electricity:

A
  • Around 50 volts is sufficient to drive a potentially lethal current through the body
  • High currents also generate lots of heat, potentially leading to electrical fires
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2
Q

Insulation

A

Electrical wires are wrapped in insulating materials to help minimise the risk of electrocution

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3
Q

Double insulation

A

If the casing of the appliance itself is not metal, it cannot become electrified. It is said to be double insulated

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4
Q

Live wire

A

Blue- Connects device to 230V mains electricity. Passes through the fuse
- alternates between a HIGH +VE and -VE Voltage of about 230V

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5
Q

Earth wire

A

Green- Connects to the Earth so that excessive charge will conduct & dissipate into the ground

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6
Q

Neutral wire

A

Brown- Completes the circuit
- Is always at 0V

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7
Q

Earthing

A
  • The precaution against static electricity
  • This means connecting a conductor to the Earth so that charge will conduct & dissipate into the ground
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8
Q

Fuse

A

A component which will break if too much current flows through it.

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9
Q

If the current in a fuse is too high…..

A
  • The temperature is higher than the wire in the fuse can take
  • & so melts breaking circuit
  • making the device safe
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10
Q

Circuit breakers

A
  • Circuit breakers detect surges in current
  • When a surge is detected, a switch is opened, immediately breaking the circuit
  • Circuit breakers can be reset by flicking the switch back to its original position
  • This makes them much more convenient than fuses
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11
Q

A current in a resistor results in the electrical transfer of energy & this heating effect is utilised in many appliances, including:

A

Electric heaters

Electric ovens

Electric hob

Toasters

Kettles

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12
Q

Equation for Power:

A

Power (W) = Current (A) x Voltage (V)

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13
Q

Equation for energy transferred:

A

Energy transferred (J) = Current (A) x Time (s) x Voltage (V)

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14
Q

DC current

A
  • All the charges move in one direction around the circuit
  • So voltage is either positive or negative
  • Provided by batteries & cells - chemical energy input
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15
Q

AC current

A
  • The charges constantly change direction (back & forth)
  • So voltage goes between being positive & negative
  • Provided by mains power supplies- electrical energy input
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16
Q

Series Circuit

A

There is only one path/loop (ignore loops with V in)

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17
Q

Parallel Circuit

A

There is more than one path/loop

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18
Q

If a component is disconnected from a series circuit…

A

The circuit is said to have been broken- it stops working

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19
Q

If a component is disconnected from a parallel circuit…

A

Current flows down a different path- it keeps working

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20
Q

Equation for Voltage:

A

Voltage (V) = Current (A) x Resistance (Ω)

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21
Q

The higher the voltage, the ……. the current

A

The higher the current

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22
Q

The more components, the ….. the resistance & the …… the current

A

The higher the resistance

& The lower the current

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23
Q

What is resistance?

A

Resistance is a measure of how much a component tries to stop current passing through it

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24
Q

As resistance increases, current ……….

A

Current decreases

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25
Variable resistor
Used to vary the current in a circuit
26
In order to test or measure the resistance of a component you must have:
A. A component (e.g. Lamp or resistor) B. A way of measuring current C. A way of measuring voltage D. A way of varying the current
27
A resistor at a constant temperature
Resistance = constant
28
Filament Lamp
Resistance = highest at high voltage, because high temperature.
29
Diode
Resistance = infinite when negative. Only allows current in one direction.
30
LDR - resistance (x) /light intensity (y) graph
LDR = Light Dependent Resistor Resistance decreases as light intensity increases. High resistance in the dark
31
Thermistor - resistance (x) /temperature (y) graph
Thermistor = Thermal-Resistor Resistance decreases as temperature increases. High resistance in the cold
32
What are Lights & LEDs used to estimate?
The current flowing through a circuit
33
Bright light, …….. current
High current
34
Dim light, ………. current
Low current
35
What is current?
The rate of flow of charge
36
What is current in metals?
The rate of flow of electrons
37
Ammeter
Connected in series with a component to measure the current, in amps, in the component
38
Equation for charge:
Charge (C) = Current (A) x Time (s) Q - quantity of charge I - intensity of current
39
Current in a series circuit
Current is the same everywhere. A1 = A2 = A3
40
Current in a parallel circuit
Current is conserved at a junction in a circuit. A1 = A2 + A3 = A4
41
Voltage in a series circuit
Components share the voltage between them V3 = V1 + V2
42
Voltage in a parallel circuit
Voltage is the same on each branch V1 = V2 = V3
43
Resistance in a series circuit
When resistors are in series, the total resistance of the circuit is increased because the pathway becomes harder for current to flow through.
44
What is voltage?
The energy difference of a charge between 2 points/ energy transferred per unit charge passed (sometimes called potential difference)
45
1 Volt =
1 Volt = 1 Joule per 1 Coulomb
46
Voltmeter
Used to measure voltage, is always placed in parallel
47
Equation for energy transferred:
Energy transferred (J) = Charge moved (C) x Voltage (V)
48
PAPER 2 What is a conductor?
- Materials that allow electrical charge to flow through them. - Most metals are good conductors of electricity
49
PAPER 2 What is an insulator?
Materials that do not allow electrical charge to flow through them
50
PAPER 2 PRACTICAL: investigate how insulating materials can be charged by friction
1. Friction can give loosely bound electrons enough energy to leave atoms & move to others 2. The electrons are transferred from one object to another 3. The object that gains electrons is given a negative charge 4. The other object loses these electrons & so gains an equal positive charge
51
PAPER 2 When is an atom neutral?
If it has the same number of protons as electrons
52
PAPER 2 If electrons are removed…
The atom becomes positively charged, since there is now an excess of protons
53
PAPER 2 If electrons are added….
The atom will become negatively charged
54
PAPER 2 Opposite charges
Attract
55
PAPER 2 Like charges
Repel
56
PAPER 2 Why is the build up of charge dangerous?
- It can cause a spark - Sparks in places with flammable materials can cause an explosion
57
PAPER 2 How does earthing work as a precaution against static electricity?
- A metal wire is a conductor - hence current will flow through it - so charge will flow from the object into the Earth
58
PAPER 2 Electrostatic induction in a negatively charged object
1. negatively charged object repels electrons in a surface 2. The surface becomes positive 3. The negative object is attracted to the positive surface
59
PAPER 2 Electrostatic induction in a positively charged object
1. A positively charged object repels electrons in a surface 2. The surface becomes negative 3. The positive object is attracted to the negative surface
60
PAPER 2 Explain electrostatic spray technology
1. A spray transfers electrons to friction 2. The spray becomes charged 3. The charges are attracted to a surface (can be by induction) 4. Because they are repelled by like charges, you get even coverage (no clumps)
61
PAPER 2 Explain photocopier technology
Static electricity is used in photocopiers - The image of the document to be copied is projected onto a positively charged image plate - Light areas of the image lose their charge, dark areas keep their charge - Negatively charged toner is attracted to the positive regions of the plate
62
Hazard: Frayed Cable
The plastic insulation is no longer intact so there is a risk of an electric shock. There may also be a short circuit which causes heating & risk of fire.
63
Hazard: Long cables
Long cables have larger resistances (Resistance is proportional to length of wire) this means that the wire will heat up and may cause a fire
64
Hazard: Damaged plugs
If plastic insulation is missing or plastic cover is broken then live wires are exposed & there will be a risk of an electric shock.
65
Hazard: Water around socket
Water can get into electrical equipment & allow for electricity to conduct to the outside & cause an electric shock
66
Hazard: Pushing metal into sockets
Metal is a very good conductor (it has free electrons) so there is a risk of an electric shock

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