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Physics > Electricity and Static Electricity > Flashcards

Electricity and Static Electricity Flashcards

1
Q

Current definition

A

Rate of flow of electric charge

ampere, A

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2
Q

Potential difference definition

A

how much energy is transferred between two points in a circuit
1V equivalent to 1J/C

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3
Q

resistance definition

A

how much a component decreases the current

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4
Q

charge definition

A

unit carrying electrical energy (Coulomb, C)

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5
Q

Why resistance increases with temperature

A

Electrons collide with ions in lattice they flow through
This causes them to vibrate and heat up
Transfers electrical energy to heat energy

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6
Q

Why resistance decreases current

A

More ions vibrate in the lattice the electrons go through, making it harder for the electrons to go through

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7
Q

Ammeter function

A

Measures current

Must be placed in series with component

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8
Q

Voltmeter function

A

Measures potential difference

Must be placed in parallel with component

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9
Q

Diode facts

A

Only lets current go in one direction

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10
Q

Thermistor facts

A

keeping supply potential difference constant gradually heats it
As temperature increases, current through thermistor increases (resistance decreases)
Useful in electronic thermostats

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11
Q

LDR facts

A

light-dependent resistor
as light level near it increases, current increases as resistance decreases
Useful in automatic night lights and burglar detectors

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12
Q

I-V graph of resistors and wires

A

Current is directly proportional to potential difference

Straight line

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13
Q

I-V graph of filament lamp

A

Increasing current increases temperature of filament, so resistance increases, causing curve
S-shape

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14
Q

I-V graph of diode

A

Current is only allowed to flow in one direction
Diode has high resistance in opposite direction
Straight horizontal line then increasing curved line

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15
Q

Series circuit facts

A

All components must be connected or whole circuit fails
Components are connected end-to-end between +ve and -ve of power supply
Total potential difference is shared between components
Total resistance increases as more components increase
Current is the same everywhere

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16
Q

Parallel circuits facts

A

Each component is connected separately to +ve and -ve of power supply
Disconnecting one component hardly affects others at all
Potential difference is the same across all components
Current is shared between branches
Total current in is equal to total current out
Total resistance decreases as you add more components in parallel

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17
Q

Fuse function

A

Uses heat created by resistance in circuit to break the circuit when it gets too hot (current gets too high)

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18
Q

How filament bulbs, toasters and electric heaters work

A

Contains as coil of really high resistance

Causes lots of thermal energy to be emitted, causing a glowing effect

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19
Q

Power definition

A

How much energy is transferred per second

20
Q

How a higher power applicant transfers less energy than a lower power appliance

A

Lower efficiency

21
Q

Power rating definition

A

Maximum amount of energy transferred between stores per second when appliance is in use

22
Q

What power transferred by an appliance is reliant on

A

Current

Potential difference

23
Q

Types of electrical supplies

A 
Batteries (d.c.)
Mains supply (a.c.)
24
Q

Alternating current

A

When the charges constantly change direction
Produced by alternating voltages (+ve and -ve ends keep alternating)
Frequency is 50Hz
UK mains supply is a.c. that supplies around 230V

25
Q

Direct current

A

Movement of charged is only in one direction

Caused by direct voltage (negative or positive but never both)

26
Q

Live wire facts

A

Brown

Carries voltage and alternating current of about 230V

27
Q

Neutral wire facts

A

Blue
Completes the circuit
Electricity flows in through live wire and out through neutral wire
Always 0V

28
Q

Earth wire facts

A

Green and yellow
For safety and protecting wiring
Carries current away if something goes wrong and stops appliance from becoming live
0V

29
Q

How plug sockets are made for safety

A

Plastic, non-conducting casing

Switches connected to live wire of circuit so circuit can be broken and risk of electric shock is reduced

30
Q

Why touching a live wire gives you an electric shock

A

Body is at 0V
If live wire is touched, large potential difference is produced across body and current flows through you
Caused large electric shock which could kill you

31
Q

Current surge causes

A

Changes in a circuit e.g. appliance switching off

Fault in an electrical appliance

32
Q

Fuses method

A

Fault develops causing live wire touching the metal case
Because case is earthed, this causes a current surge
This melts fuse, isolating whole appliance from live wire
Done so electric shock or a fire is impossible
Fuses should be rated but just above normal operating current
Larger current, thicker cable so cable doesn’t get too hot and melt

33
Q

Circuit breakers method

A

Large current trips (turns off) a circuit breaker
They turn off quicker than time taken for fuse to melt
Can also be reset, more convenient than replacing a fuse
Circuit breakers are more expensive than fuses

34
Q

Double insulated appliances

A

Appliances with a plastic casing and no metal parts showing
Don’t need an earth wire
Connected to a two-core cable (only live and neutral)

35
Q

How static is built up by friction

A

Insulating materials are rubbed together
Negatively-charged electrons are scraped off one and dumped on the other
Cannot move as sandwiched between insulators so they build up
This gives both materials charge as both have lost or gained electrons

36
Q

How electrically charged object (e.g. a balloon) can attract uncharged objects e.g. (a wall)

A

Attraction by induction
Balloon is rubbed onto something to build static
Its negative charges repel negative charges on surface of wall
Leaves a positive charge on surface of wall, attracting balloon

37
Q

How static causes sparks

A

Static builds up on an object
If potential difference between that object and something else is
large enough, electrons can jump across the gap between charged object and earth, causing a spark
Only usually happens when gap is small

38
Q

Static electricity used

A

Photocopiers
Reducing dust and smoke from industrial chimneys
Electrostatic sprayers

39
Q

Electrostatic sprayers method

A

Spray gun is charged, charging up small drops of liquid
Each drop of liquid repels the other, resulting in very fine spray
Object may be given an opposite charge, attracting fine spray of liquid
If not, objects become charged by induction, attracting drops of liquid

40
Q

Static electricity danger in refuelling cars

A

Fuel flowing out of filler pipe can build up static

This can cause a spark, igniting fuel and causing an explosion

41
Q

Static electricity dangers on airplanes

A

Friction between air and plane causes plane to become charged
Static can the interfere with communication equipment

42
Q

Static electricity dangers in lightning

A

Raindrops and ice bump together in storm cloud
This leaves top of cloud positively-charged and bottom of cloud negative, creating huge potential difference
Creates a spark (lightning), which can damage houses and start fires

43
Q

Earthing definition and function

A

Connecting a charged object to the ground using a conductor
Provides an easy route to the ground, so no charge is built up
Electrons flow up from ground if charge is positive or vice verse if negative
Fuel tankers must be earthed to prevent sparks causing fuel to explode

44
Q

Electric field definition

A

region created by any electrically-charged object in which a force would be exerted on any charged objects placed within it

45
Q

Electric field diagram rules

A

Closer to object, stronger field
Field lines go from positive to negative
Lines are right angle to surface of object
Closer lines, stronger field

Physics (7 decks)

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