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IGCSE PHYSICS > Unit 3 - Electricity > Flashcards

Unit 3 - Electricity Flashcards

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1
Q

What do we use to measure currant

A

Ammeter

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2
Q

Unit of measure for charge (Q)

A

Coulomb (C)

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3
Q

Unit of measure for energy (w)

A

Joules (J)

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4
Q

What do we use to measure resistance (Ω)

A

Ohms (Ω)

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5
Q

Unit of measure for time (s)

A

Seconds (s)

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6
Q

Unit of measure for voltage (V)

A

Volts (V)

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7
Q

Unit of measure for power (P)

A

Watts (W)

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8
Q

What are the hazards of electricity

A

Frayed cables (fire/electrocution), long cables (tripping), damaged plugs (fire/electrocution), water around sockets, pushing metal things into sockets (electrocution)

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9
Q

What is insulation

A

Provides a protective layer around electric wires to prevent the conduction of electricity under the influence of an electric field

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10
Q

What is double insulation

A

When the wire AND casing have a plastic cover. This stops the wire from touching the casing when the casing is an electrical conductor

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11
Q

What is earthing

A

The 3rd wire is the earthing wire. It runs current into the ground to stop current circulating on the outside (causing shocks)

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12
Q

What are circuit breakers

A

An electromagnetic switch that opens or trips when there is too much current (breaking the circuit but can be put back)

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13
Q

What is a fuse

A

Fuses contain a thin wire that melts when a certain amount of current passes through it. This permanently brakes the circuit stopping a power over,lad

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14
Q

Power =

A

P = I X V

Power (w) = current (A) X voltage (V)

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15
Q

Energy transferred =

A

E = I X V X t

Energy transferred (J) = current (A) X voltage (V) X time (s)

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16
Q

Voltage =

A 
V = W / Q
Voltage (V) = energy (J) / charge (C)
OR
V = I X R
Voltage (V) = current (I) X resistance (Ω)
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17
Q

Current =

A

I = Q/ S

Current (A) = charge (C) / time (s)

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18
Q

Resistance =

A

Ω = V / I

Resistance (Ω) = voltage (V) / current (A)

19
Q

Properties of mains electricity

A

They are A.C (alternating current). This means that the voltage / current switches directions 50 cycles per second.
It’s always 230V in the UK

20
Q

Properties of direct current

A

Direct current (D.C) mains are powered by a battery which provides a direct current that flows in one direction at a constant rate

21
Q

Rules of a series circuit

A

Current is equal throughout
Current depends on the applied voltage
Voltage throughout the components add up to the voltage supplied
If one appliance fails, the whole circuit fails

22
Q

Rules of a parallel circuit

A

Voltage is equal throughout each loop
Current splits and the junctions. Total current at the junction equals the total current supplied
If one appliance fails, only that loop fails

23
Q

What is current

A

The rate of the flow of electrons

24
Q

What is voltage

A

The energy transferred per unit charge passed
ie.
1 volt = 1 joule per coulomb
20 V = 20 J per C

25
Q

What is Ohms law

A

(Only works for ohmic conductors)
For conductor at a a constant temperature, the current is proportional to the voltage across it.
Straight line in a I/V graph

26
Q

Give some examples of ohmic conductors

A

Wires

Resistors

27
Q

What is a non-ohmic conductor

A

Does not obey ohms law. Curved I/V graph

28
Q

Give some examples of non-ohmic conductors

A 
Filament bulbs (because they heat up to much)
Any type of diode
Non-ohmic resistors (eg thermosister)
29
Q

Effect of resistance on current

A

More resistance = less current can flow

30
Q

Unit for current (I)

A

Amps - A

31
Q

How to LDRs work

A

Light dependant resistors

More light = less resistance

32
Q

How to thermistors work

A

More temperature = less resistance

33
Q

What are lamps and LED used to show

A

Lamps and LEDs are used to indicate the presence of currant in a circuit.
More currant = brighter light

34
Q

Charge =

A

Q = I X t

Charge (C) = current (A) X time (s)

35
Q

What is an electric current

A

The flow of negatively charged electrons or of ions

36
Q

Common electrical conductors

A

Metals

Water

37
Q

Common electrical insulators

A

Plastic

Air

38
Q

What types of charges attract/repulse

A

Opposite charges attract (+/-)
Similar charges repulse (+/+ or -/-)

They do this because together they become neutral

39
Q

How are electrostatic charges produced

A

By the loss or gain of electrons
Loss = positive charge
Gain = negative charge

40
Q

Describe experiments to show how insulators can become charged by friction

A

Cloth on balloon, balloon becomes charged, balloon sticks to wall

41
Q

Explain the electrostatic phenomena in terms of the movement of electrons

A

Friction pulls electrons out of one object and into another

42
Q

Potential dangers of electrostatic charges

A

When refuelling.
When a tanker moves through the air, the friction between the air and tanker causes the tanker to become charged. When you attach the metal nozzle to refuel, there could be a spark. This would ignite any fuel vapours causing a fire. To avoid this, and earthing wire is used

43
Q

Uses of electrostatic charges

A

Photocopiers
Inkjet painting - all the pain droplets are given a similar charge (repeal each other forming a fine mist) and the car body is given an opposite charge (attracting the paint). This gives an even coating

IGCSE PHYSICS (8 decks)

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