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physics igcse > electricity > Flashcards

electricity Flashcards

1
Q

What is a current? (amps) (A)

A

The rate of flow of charge round the circuit

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2
Q

What charge are electrons?

A

Negatively charged particles

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3
Q

What is the voltage (volts) (v)

A

What drives the current around
“electrical pressure”
-Amount of energy transferred per unit of charge

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4
Q

Resistance (ohm)

A

-Anything in the circuit which slows the flow down
-If you add more components, higher overall resistance

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5
Q

Another name for voltage:

A

Potential difference

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6
Q

If you increase voltage…

A

More current will flow

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7
Q

If you increase resistance…

A

Less current will flow

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8
Q

What does an ammeter measure:

A

The current flowing through the component

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9
Q

Rule for ammeter in series:

A
  • Can be placed anywhere in the main circuit
    -Current stays the same
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10
Q

Voltmeter

A

-Measures the voltage across the component
-Must be placed in parallel around the component not the variable resistor or the battery.

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11
Q

rules for series:

A

-The component, the ammeter, and the variable resistor are all in series, which means they can be put in any order

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12
Q

rule for parallel:

A

-the voltmeter can only be placed in parallel around the component under test.

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13
Q

voltage formula

A

voltage= current x resistance

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13
Q

Rules for gradient graphs:

A
  • The gradient of an IV graph shows you how the resistance of the component behaves
    -The steeper the graph the lower the resistance
    -If the graph curves, it means the resistance is changing
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14
Q

Four important current-voltage graphs

A

-wire/fixed resistor
-Bulb/lamp
-LED/diode
-LDR

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15
Q

LED (light emitting diodes)

A
  • emit light when a current flows through them
    -used for numbers…traffic lights
    -Dn’t have a filament that can burn out
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16
Q

Components that can change resistance
Light dependent resistor

A

-LDR- changes its resistance based on how much light falls
-In bright light, less resistance
-In dark light, more resistance

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17
Q

Thermistor:
Temperature dependent resistor

A

-In hot conditions, resistance drops
-In cool conditions, resistance goes up

18
Q

Series vs Parallel
Series:

A
  • The different components are connected in a line, end to end
    -If you remove or disconnect one component, the circuit is broken and it stops working.
19
Q

Series vs Parallel
Rules for series: 5 points

A
  • Bigger supply p.d when more cells are in series
    -Current is the same everywhere
    -Size of current depends on total potential difference and resistance of circuit
    -Voltage of the supply is shared between components
    -Total resistance of the circuit depends on number of components and the type of components used.
    Total R= R1+R2+R3
20
Q

Series Vs Parallel
Parallel:

A
  • each component is separately connected to the +ve -ve of supply, except for ammeters which are always connected
    -If you remove one component, it will hardly affect the others
    -The potential difference is the same across all branches V1=V2
    -Current is shared between branches. Total current= total of all the current flowing through separate components
    -The current depends on resistance. Higher resistance= harder for charge to flow
21
Q

Charge

A

Current is the rate of flow of electrical charge
-Charged is carried by negatively charged electrons.
charge= current x time

22
Q

When a charge drops through a voltage…

A

It transfers energy.
-Energy is supplied to charge at power source
-The bigger the change in voltage, the more energy is transferred for a given amount of charge.
-A battery with a bigger voltage will supply more energy to the circuit for every coulomb of charge which flows round it
-More charge, more energy transferred into circuit

23
Q

What is equation for energy transferred?

A

energy transferred= charge x voltage

24
Q

Energy transferred with a resistance:

A

energy transferred= charge x current x resistance

25
Q

Electrical safety:
three wires in a plug

A
  • Live
  • Neutral
  • Earth
26
Q

Electrical safety:
Rule of wires

A

Live wire: alternates between high voltage and low voltage
Neutral: Always at 0V
Earth wire/ fuse: just for safety and work together

27
Q

Electrical safety:
Earthing

A

Case must be attached to an earth wire. An earth conductor can never become live

28
Q

Electrical safety:
Double insulated

A

If an appliance has a plastic casing and no metal parts showing

29
Q

Earthing protection steps:

A

-If fault develops and the live touches metal case, because case is earthed, current flows through live, the case and earth wire
-The surge in current blows the fuse which cuts of live supply
-Impossible to get electric shock. Prevents risk of fire

30
Q

Circuit breakers vs Fuses:
Circuit breakers

A

Electrical safety devices used in some circuits
- When circuit breakers detect a surge in current, they break circuit by opening a switch.
- Circuit breaker can easily be reset by flicking a switch on the device unlike fuses which need to be replaced when melted.
-safer: immediately break as soon as there is current surge

31
Q

Energy and power:
Resistor

A
  • Resistors get hot when there is an energy transfer
    -Electrons collide with the ions in the lattice that make up resistor which gives ions energy ( vibrate and heat up)
    -heating effect increases resistor’s resistance- so less current will flow
    -Heating effect can cause other components to melt (eg fuses)
    -
32
Q

Electricity power and Fuse:
definition

A

-Electrical power is the rate at which appliance transfers energy
-An appliance with a high power rating transfers a lot of energy in a short time

33
Q

Electric Power equation:

A

power= current x voltage

34
Q

Electric power and fuse:
Fuse

A

To work out fuse needed… you need to work out current that the item will normally use.
-Fuse should be rated a little higher than the normal current.

35
Q

Energy transferred:

A
  • Power of appliance and how long it is on for (seconds)
36
Q

Static electricity:
Rule of charge (3 points)

A
  • Opposite charges attract
    -Two things with same charge repel
    -Forces get weaker the further apart two things are
37
Q

Static charge meaning

A

-A charge which builds up in one place and is not free to move
-Common on insulators, where current cannot flow

38
Q

Cause of static electricity

A

Friction
-When two insulating materials are rubbed together, electrons will be scraped off one and dumped on the other
-Leaves a positive electrostatic charge and a negative elec… charge.

39
Q

both +ve and -ve charges are only produced by movemement of…

A

electrons
-positive charge does not move
-positive static charge is caused by electrons moving elsewhere

40
Q

Static electricity:
Conductors

A
  • Static charges can occur on conductors too
    -Cars often get a static charge on the outside because they’ve gained /lost electrons
41
Q

Static electricity:
Conductors

A
  • A charged conductor can be discharged safely by connecting it to earth with a metal strap
    -Electrons flow down the strap i=to the ground if charge is negative and up from the ground if charge is positive.
42
Q

As charge builds up…

A

so does voltage
- An electric charge builds on an isolated object the voltage between the object and earth increases
- if the voltage is large enough, electrons can jump across gap between charged object and earth- spark.

43
Q

Practical:
Investigating static electricity
(polythene and acetate)

A
  • Rub on cloth
    -When polythene rubs with duster
    -Electrons move from duster to rod
    -Duster is negative, rod is positive

physics igcse (8 decks)

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