safety / intro the mains supply and batteries are sources of electrical energy electrical appliances...
TRANSCRIPT
![Page 1: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/1.jpg)
Safety / Intro
• The mains supply and batteries are sources of Electrical Energy
• Electrical Appliances are Energy Changers
![Page 2: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/2.jpg)
Power
• Heat producing appliances have a power rating greater than 1000 Watts
• Power Rating is the amount of energy used per second
• Appliances greater than 700 W are protected by a 13 A fuse
![Page 3: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/3.jpg)
Fuses
• This protects the flex from overheating, melting and causing a fire.
• Fuses are connected to the LIVE pin.
• When the fuse blows it isolates the appliance from the ‘high voltage’ supply
![Page 4: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/4.jpg)
Plugs
• Mains Plugs
![Page 5: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/5.jpg)
Human Conductivity
• We conduct electricity very well
• When wet the body’s conductivity increases
• Bathroom light switches, shower switches are either outside the bathroom or on a cord
![Page 6: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/6.jpg)
Earth Wire
• Connected to casing of metal appliances
• If live wire touches the casing ‘ current flows through earth wire to ground ( often via the water pipes )
• A large current flows , blowing the fuse and isolating the appliance from the high voltage mains.
![Page 7: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/7.jpg)
Double Insulation
• Appliances with casings made of plastic DO NOT need an earth wire
• The casing is an insulator
![Page 8: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/8.jpg)
Electric Current
• This is a Flow of Charged Particles
»Q = I x t
• Charge Current Time
• Coulombs ( C ) Amps ( A ) Seconds ( s )
![Page 9: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/9.jpg)
Voltage
• Energy Given to each coulomb of charge
• Units are Volts ( V )
• Measured by Voltmeter ,
• Connected in parallel
![Page 10: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/10.jpg)
Current
• This is a flow of Charged Particles
• Units are Amps, ( A )
• Measured using an Ammeter
• Connected in Series
![Page 11: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/11.jpg)
Series Circuits
• Current is the SAME at ALL points
• Voltage across Supply equals the voltage across Resistor 1 + voltage across resistor 2
• Vs = V1 + V2
![Page 12: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/12.jpg)
Parallel Circuits
• Voltage across each branch is the same
• Current through resistor 1 plus current through resistor 2 equals the supply current
• It = I1 + I2
![Page 13: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/13.jpg)
Resistance
• Ohm’s Law V = I x R at constant Temp
• Resistance : measure of how easy it is for charges to flow.
» V = I x R
» Volts ( V ) Amps ( A ) Ohms ( Ω
![Page 14: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/14.jpg)
Series Resistors
321 RRRRs ++=
![Page 15: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/15.jpg)
Parallel Resistors
321
1111
RRRRp++=
![Page 16: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/16.jpg)
Variable Resistors
• A length of wire is wrapped into a cylinder
• Different lengths can be tapped into
• The longer the length the bigger the resistance
• The bigger the resistance the lower the current
![Page 17: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/17.jpg)
Variable Resistors
• Uses
• Light Dimmer Switches
• Volume controls
• Speed Controls
• Temperature Controls for grills/ ovens …
• Computer Joysticks
• Fuel gauges
![Page 18: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/18.jpg)
Continuity Tester
Used to detect ‘Open Circuits’ or Breaks in Circuits such as blown bulbs.
Component is blown if there is NO reading on the meter.
![Page 19: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/19.jpg)
Power
This is the amount of energy transferred per second. Units are Watts ( W ).
Heat producing appliances have big power ratings
( )sJWondperjouleoneisWattOnet
EP
Time
TranferredEnergyPower
/=sec
==
11
![Page 20: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/20.jpg)
Power
• Power can also be calculated from
R
VPceresissquaredVoltagePower
RxIPceresisxsquaredCurrentPower
IxVPCurrentxVoltagePower
2
2
=tan÷=
=tan=
==
![Page 21: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/21.jpg)
Lamps
• Discharge Lamps ( Fluorescent Tubes )• An electric current passes through the gas• Virtually NO heat Energy is produced• MUCH more efficient than• Filament lamps• An electric current is passed through a piece of
resistance wire which heats up• Produces more heat energy than light energy
![Page 22: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/22.jpg)
Direct Current
• Current flows in one direction ONLY
• Electrons flow from Negative to Positive
• Size of Voltage remains constant
• Batteries supply D.C.
![Page 23: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/23.jpg)
Alternating Current
• Mains electricity is A.C.• The current constantly changes direction• Mains electricity is 50 Hz , 50 cycles in 1 second• The size of the voltage is constantly changing.
Quoted value ( 230 V mains )is smaller than the peak value
Quoted value, 230 V
Current flows when below 0V line
Peak value, 325 V for mains
0V Line
![Page 24: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/24.jpg)
Behind the Wall
• Household appliances are connected in parallel : same voltage ( 230 V ) and independent switching
• Sockets are wired in a RING circuit:• Current flows via 2 paths therefore smaller
currents flow and thinner cable can be used• Less cable needed than conventional parallel• Easy to add extra sockets
![Page 25: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/25.jpg)
Behind the Wall
• Lighting circuit draws less current than Ring circuit for sockets
• Lighting circuit conventional parallel
• Lighting circuit uses a 10A circuit breaker as opposed to a 30A on the ring circuit
![Page 26: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/26.jpg)
Fuses / Circuit Breakers
• Mains fuses protect the mains wiring
• Circuit Breaker is an automatic switch that switches off when current exceeds stated value
• Circuit breakers can easily be reset and used again but fuses must be replaced
![Page 27: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/27.jpg)
Kilowatt Hours
• I unit of electricity is 1kWh• I.e. A 1kW appliance switched on for 1 hour• total units = Power (kW) x time ( hours )
• 1 kWh = Power x time» 1000 W x 60 x 60 seconds » = 3 600 000 Joules
![Page 28: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/28.jpg)
• aElectromagnetism
• When a current flows there is a Magnetic Field around a wire
• If a wire is placed inside a magnetic field it experiences a force
N SS N
Current flows out of board
S NCurrent flows into board
![Page 29: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/29.jpg)
Electromagnetism
• Relays
• Motors
• Bells
• Loudspeakers
• Tape Recorders
• All use Electromagnetic effect
![Page 30: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/30.jpg)
d
• a
The d.c. motor
• Each side of the coil experiences forces acting in opposite directions the coil rotates
NN
SS+VE+VE
-VE-VE
88
Rotation isproduced
Rotation isproduced
![Page 31: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/31.jpg)
a
• a
d.c. motor
• If the flow of current WAS NOT reversed then the coil would flip back
• A SPLIT RING COMMUTATOR reverses the flow of current
99
NN+VE+VE
-VE-VE
SS
![Page 32: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/32.jpg)
a
• b
The d.c. motor
• The coil continues to rotate
NN
SS+VE+VE
-VE-VE
![Page 33: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/33.jpg)
Commercial motors
• More coils : more powerful motor, smoother turning
• Electromagnets instead of permanent magnets : increased magnetic field, switched on / off
• Brushes as contacts : mould themselves to shape of commutator
![Page 34: Safety / Intro The mains supply and batteries are sources of Electrical Energy Electrical Appliances are Energy Changers](https://reader035.vdocuments.site/reader035/viewer/2022062511/551bc3e8550346af588b4ca6/html5/thumbnails/34.jpg)
Commercial motors
•