Topic 7 - Electricity in the home Flashcards
What is the currnet from a cell ?
-It is the direct current (DC) .
-Eelctrons only trvale in one direction .
What is mains electricity ?
-Mains electriicty is an alternating current (AC )
-The current is constantly chngin direction .
What is the benefit of AC ?
-It is very easy to use a transformer to increase or decrease the potential differenc eof Ac . Harder to do in DC .
What is the frequency of alternating current in the UK ?
50Hz
What is the potential difference of alternating current in the Uk ?
230 Volts .
What can you use to see the pattern of eelctrical current
an oscilliscope .
Check sheet
Look at AC and DC curent .
-In alternating current , the potential difference is rising and falling .
-Showing current going backwards and forwards .
-The potential difference does not change with DC .
-The hieght of the peka shows the maximum potential differnece =230 V.
-We can use the oscilliscope to calculae the frequencyof algternating current .
-Time from one peak ot another shows one cycle .
1st peak 0.01
Next peak 0.03
0.03-0.01=0.02 time it takes or current to chane and then turn back again .
Frequency is 1/0.02 = 50Hz
time on bottom !
What are electrical supplies in the Uk connected to ?
-The mains supplu . USing three core cables .
There are THREE wires .
-Each wirse is made of copper which is a good conductor of insulator ,
-The coating of wire are made of plastic which does not conduct electricity .
What is the brown wire
THAT IS THE LIVE WIRE .
-Carries the alternating potential differnece from the suplly (230V) .
-The live wire is connected to a fuse in the plug .
What is the Blue wire - neutral .
It completes the circuit , Potential difffernece =0V compred to the live wire .
What is the green / yellow striped wire .
Earth wire this is a safety wire that stops the appliance beocmign live .
What is the neutral wire .
complestes the circuit .
-the potential difference 0V compared to the live wire .
-What is the green /yellow striped wire .
Earth wire - this is a safety wire that stops the appliance from becoming live
Check the sheet what is it and what dpes ot swp
-A simple circuit wth the main supplky .
-Live wire carries 230 V elecricity from generators . (live wire is connected t a fuse .)
-energy is transferres ad the electricla current passes through the applaince .
-The neutrla iwre completes the circuit .
How could the live wire be extreemly dangeours ?
-It could be fatal if touched .
-Even with the OPEN switch . As the first part of te lvie wire running inot the switch still has a potenital differnece of 230 V .
What about p.d of Earth ?
-The potential difference of theEarth is 0 volts .
-So if someone touched the live wire , a current would flow thoruhg the person +into the Earth and they would be electrocouted .
How can ppliances with metal cases be very dangerous ?
-As the lvie wire becomes loosee and touches the metl case , the case can become live .
-cOULD BE FATAL IF SOEMOEN TOUCHED HTE LIVE WIRE .
solution to METAL cases ?
Therreofre , the emtal case is attached to the Earth wire . The Earth wire is connected to the ground with a metal rod .
-So if the case beovmes live , a huge current fows to the Earth . The fuse melts and shuts off the current .
-Preventing qnyone from getting an electric current from touching the case .
In exam , what are the only energy transfwrs we need to know ?
-Kinetic energy and thermla neergy .
What does a BLENDER and a FAN TRANSFER ?
-These are both powered by electrical energy and is transerred to kinetic energy in the motors .
-As the main purpose of oth of these appliances is movement .
What does an IRON and KETTLE transfer ?
Transfers ELECTRICAL ENERGY into THERMAL ENERGY .
-As both appliances are designed to get hot .
What does a HAIR DRYER AND A WASHIGN MACHIEN transfer ?
They transfer eectricl ennergy into kinetic energy OF ELECTRICAL MOTORS and THERMAL ENERGY.
What is power ?
-Power is the rate at whie energy is transferred .
-1WATT is an energy transsfer of 1J per second .
-Applainces used to GENERATE THERMAL ENRGY , usually have a much higher power rating than appliances designed to create kinetic energy .
-How can we calculagte hte pwoer of a componenet ?
-If we know both the POTENTIAL DIFFERNECE a
cross a component nd the current flwoing thorugh it .
-We can calculate the power of a component using this equation
CHECK SHEET
Power = Potential difference *Current
Watts Volts Amps
Do the quiestion oon the sheet
.
How do we work out the pwoer of a componeent but we only know RESISTANCE not p.d ?
If we know the current though a component and the resitance of a component , we can calculate power like this
Power = I(2)* r
Watts Current Ohms
Electrical charge in circuits ?
-Electrical charge is measured in coloumbs (C) .
-A current is 1 ampere = 1 Coloumb of charge flowing per second ..
-The size of the electric currnet is the rate of flow of the electric harge .
Equariton of elecrricla charge ?
Q =I*T
QIT trinagle
Charge flow (c)=Icurrent (a) *Ttime (s)
DO THE QUESTION ON SHEET .
HOW DO YOU CALCULATE ENERGY TRANSFERS IN COMPONENTS ?
E =Q*V
Eneegyr transferred () *V potenitl difference (v)
DO THE QUESTION ON THE SHEET .
-WHEN CHARGE FLOWS THORUHG A RESISOTR , ENERGY IS TRANSFERRED OT THE RESISTOR , SO THE RESISTOR BECOMES HOTTER .
./…
What is efficency ?
-Efficencu is used to tell us what fraction of the energyw e put into an appliace is transferred into useful forms of enrgy .
HOW TO CALCULATE EFFICENCY ?
Usefuloutput /total input *100
Cannoot get an efficency more than a hudnred percern or more than one SO OTHERWISE IT WORNG .
How ot workout energy transferred by an appliacne ?
Energy = pwoer time
E=pt
DO practice question
CONVERT TO KJ WHERE POSSIBLE .
