Electricity - created from Mind Map

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CIRCUITS- THE BASICS

RESISTANCE

LDR's, THERMISTORS AND LED's

SERIES AND PARALLEL CIRCUITS

CHARGE, VOLTAGE AND ENERGY CHANGE

ENERGY AND POWER IN CIRCUITS

STATIC ELECTRICITY

The Properties of a Circuit

Test Circuit

Mains Supply is a.c., Battery Supply is d.c.

CURRENT IS THE RATE OF FLOW OF CHARGE

VOLTAGE IS WHAT DRIVES THE CURRENT. "ELECTRICAL PRESSURE"

RESISTANCE IS ANYTHING IN THE CIRCUIT WHICH SLOWS THE FLOW DOWN.

ELECTRONS USUALLY CARRY THE CHARGE

CURRENT WILL ONLY FLOW THROUGH A COMPONENT IF THERE IS A VOLTAGE ACROSS THAT COMPONENT

ALSO KNOWN AS POTENTIAL DIFFERENCE

IF YOU INCREASE THE VOLTAGE- THEN MORE CURRENT WILL FLOW

IF YOU ADD MORE COMPONENTS TO THE CIRCUIT THERE WILL BE A HIGHER OVERALL RESISTANCE

IF YOU INCREASE THE RESISTANCE- THEN LESS CURRENT WILL FLOW

THE AMMETER

THE VOLTAGE

MEASURES CURRENT [IN AMPS] FLOWING THROUGH THE COMPONENT

MUST BE IN SERIES

MEASURE THE VOLTAGE [VOLTS] ACROSS THE COMPONENT

MUST BE IN PARALLEL

UK MAINS =230 VOLTS

A.C = ALTERNATING CURRENT [CHANGING DIRECTION]

CELLS AND BATTERIES= D.C [SAME DIRECTION]

Graphs

Current-Voltage Graphs

VOLTAGE= CURRENT * RESISTANCE

GRADIENT OF AN I-V GRAPH SHOWS YOU HOW THE RESISTANCE OF THE COMPONENT BEHAVES. STEEPER = LOWER RESISTANCE

CURVES = RESISTANCE IS CHANGING

WIRE

DIFFERENT RESISTORS

DIODE

METAL FILAMENT LAMP

THE CURRENT THROUGH A WIRE [ CONSTANT TEMP] IS PROPORTIONAL TO VOLTAGE

CURRENT THROUGH A RESISTOR IS PROPORTIONAL TO VOLTAGE. DIFFERENT RESISTORS HAVE DIFFERENT RESISTANCES, HENCE THE DIFFERENT SLOPES

CURRENT WILL ONLY FLOW THROUGH A DIODE IN ONE DIRECTION

AS TEMPERATURE INCREASES, THE RESISTANCE INCREASES= CURVE

LED's

LDR's

Thermistor

EMIT LIGHT WHEN A CURRENT FLOWS THROUGH THEM IN THE FORWARD DIRECTION

THEY ARE USED IN DIGITAL CLOCKS, TRAFFIC LIGHTS, AND IN REMOTE CONTROLS.

NO FILAMENT SO THAT THEY CANT BURN OUT

USED TO KNOW IF A CIRCUIT IS WORKING

IS A SPECIAL TYPE OF RESISTOR THAT CHANGES ITS RESISTANCE DEPENDING ON HOW MUCH LIGHT FALLS

BRIGHT LIGHT= LOW RESISTANCE

DARKNESS= HIGH RESISTANCE

BURGLAR DETECTORS

TEMPERATURE- DEPENDENT RESISTOR

HOT CONDITIONS= RESISTANCE DROPS

COLD CONDITIONS= RESISTANCE GOES UP

TEMPERATURE DETECTORS- THERMOSTATS

Series Circuit

Parallel Circuit

DIFFERENT COMPONENTS ARE CONNECTED IN A LINE, END TO END, BETWEEN THE +VE AND -VE POWER SUPPLY

REMOVING OR DISCONNECTING ONE COMPONENT, THE CIRCUIT IS BROKEN AND THEY ALL STOP WORKING.

MORE COMPONENTS= BIGGER P.D.

CURRENT IS THE SAME EVERYWHERE

TOTAL RESISTANCE= RESISTANCE 1 + RESISTANCE 2 + .....

P.D IS SHARED BETWEEN COMPONENTS. P.D OF EACH COMPONENTS ON ITS RESISTANCE

EACH COMPONENT IS SEPARATELY CONNECTED TO THE +VE AND -VE OF THE SUPPLY

REMOVING OR DISCONNECTING ONE COMPONENT, NO EFFECT WILL OCCUR TO THE OTHERS

CARS, HOUSEHOLD ELECTRICS, HOUSE LIGHTS

P.D. IS THE SAME CROSS ALL BRANCHES

CURRENT IS SHARED BETWEEN BRANCHES

IF TWO COMPONENTS ARE IDENTICAL IN PARALLEL= SAME CURRENT

TOTAL RESISTANCE OF THE CIRCUIT DECREASES IF YOU ADD A SECOND RESISTOR IN PARALLEL

Charge Through a Circuit Depends on Current and Time

When a Charge Drops Through a Voltage it Transfers Energy

IN SOLID METAL CONDUCTORS [COPPER WIRE] CHARGE IS CARRIED BY NEGATIVELY CHARGED ELECTRONS

WHEN CURRENT FLOWS PAST A POINT IN A CIRCUIT FOR A LENGTH OF TIME THEN THE CHARGE THAT HAS PASSED IS GIVEN BY ...

CHARGE= CURRENT * TIME

VOLTAGE IS THE ENERGY TRANSFERRED PER UNIT CHARGE PASSED

ONE VOLT IS ONE JOULE PER COULOMB

ENERGY TRANSFERRED= CHARGE * VOLTAGE

ENERGY TRANSFERRED= CHARGE * CURRENT * RESISTANCE

BIGGER CHANGE IN VOLTAGE= MORE ENERGY IS TRANSFERRED FOR A GIVEN AMOUNT OF CHARGE PASSING THROUGH THE CIRCUIT

Resistors Get Hot When an Electric Current Passes Through Them

Electrical Power and Fuse Ratings

WHEN ELECTRIC CURRENT IS IN A RESISTOR THERE IS AN ELECTRIC TRANSFER WHICH HEATS THE RESISTOR.

THIS HAPPENS AS A RESULT OF THE ELECTRONS COLLIDE WITH THE IONS IN THE LATTICE THAT MAKE UP THE RESISTOR AS THEY FLOW THROUGH IT. THIS GIVES THE IONS ENERGY , WHICH CAUSES THEM TO VIBRATE AND HEAT UP

THIS HEATING EFFECT INCREASES THE RESISTOR'S RESISTANCE - LESS CURRENT WILL FLOW, OR A GREATER VOLTAGE WILL BE NEEDED TO PRODUCE THE SAME CURRENT

THE HEATING EFFECT CAN CAUSE COMPONENTS IN THE CIRCUIT TO MELT- WHICH MEANS THE CIRCUIT WILL STOP WORKING. FUSES USE THIS EFFECT TO PROTECT CIRCUITS- THEY MELT AND BREAK THE CIRCUIT IF THE CURRENT GETS TOO HIGHT

TOASTERS CONTAIN A COIL OF WIRE WITH A REALLY HIGH RESISTANCE - TEMPERATURE RISES AND GLOWS.

ELECTRICAL POWER IS THE RATE AT WHICH AN APPLIANCE TRANSFERS ENERGY.

Electrical Appliances Transfer Energy Electrically

AN APPLIANCE WITH A HIGH POWER RATING TRANSFERS A LOT OF ENERGY IN A SHORT TIME

ENERGY COMES FROM THE CURRENT FLOWING THROUGH IT. THIS MEANS THAT AN APPLIANCE WITH A HIGH POWER RATING WILL DRAW A LARGE CURRENT FROM THE SUPPLY

POWER IS MEASURED IN WATTS (W). ELECTRICAL POWER = CURRENT * VOLTAGE

FUSES SHOULD BE RATED HIGHER THEN THE NORMAL OPERATING CURRENT

ENERGY TRANSFERRED= CURRENT * VOLTAGE * TIME

ENERGY TRANSFER BY AN APPLIANCE DEPENDS ON THE POWER OF THE APPLIANCE AND HOW LONG IT IS ON FOR ENERGY TRANSFERRED = ELECTRICAL POWER * TIME

Like Charges Repel, Opposite Charges Attract

Conductors Conduct Charge- Insulators Don't

A Static Charge Cannot Move

As Charge Builds Up, So Does the Voltage

THESE FORCES GET WEAKER THE FURTHER APART THE TWO THINGS ARE

MATERIALS THAT ARE ELECTRICAL CONDUCTORS CONDUCT EASILY- A CURRENT CAN FLOW THROUGH THEM. THEY'RE USUALLY METALS E.G. COPPER AND SILVER

ELECTRICAL INSULATORS DON'T CONDUCT CHARGE VERY WELL- SO A CURRENT CAN'T FLOW. EXAMPLES INCLUDE PLASTIC AND RUBBERR

STATIC CHARGE IS A CHARGE WHICH BUILDS UP IN ONE PLACE AND IS NOT FREE TO MOVE. THESE ARE MORE COMMON ON INSULATORS, WHERE CURRENT CANNOT FLOW, RATHER THAN ON CONDUCTORS.

COMMON CAUSE OF STATIC ELECTRICITY IS FRICTION- TWO INSULATING MATERIALS ARE RUBBED TOGETHER, ELECTRONS WILL BE SCAPED OFF ONE AND DUMPED ON THE OTHER.

+VE ELECTROSTATIC CHARGE ON ONE END AND A -VE ELECTROSTATIC CHARGE ON THE OTHER

+VE CHARGES DO NOT MOVE.

ELECTROSTATIC CHARGES CAN OCCUR ON CONDUCTORS AS WELL

ELECTRIC CHARGEBUILDS ON AN ISOLATED OBJECT, THE VOLTAGE BETWEEN THE OBJECT AND THE EARTH INCREASES.

VOLTAGE GETS LARGE ENOUGH, ELECTRONS CAN JUMP ACROSS THE GAP BETWEEN THE CHARGED OBJECT AND THE EARTH= SPARK.

THEY CAN ALSO JUMP TO ANY EARTHED CONDUCTOR THAT IS NEARBY= STATIC SHOCKS.