Topic 7 - Electricity in the home

Question 1

What is the currnet from a cell ?

Answer 1

-It is the direct current (DC) .
-Eelctrons only trvale in one direction .

Question 2

What is mains electricity ?

Answer 2

-Mains electriicty is an alternating current (AC )
-The current is constantly chngin direction .

Question 3

What is the benefit of AC ?

Answer 3

-It is very easy to use a transformer to increase or decrease the potential differenc eof Ac . Harder to do in DC .

Question 4

What is the frequency of alternating current in the UK ?

Answer 4

50Hz

Question 5

What is the potential difference of alternating current in the Uk ?

Answer 5

230 Volts .

Question 6

What can you use to see the pattern of eelctrical current

Answer 6

an oscilliscope .

Question 7

Check sheet
Look at AC and DC curent .

Answer 7

-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.

Question 8

-We can use the oscilliscope to calculae the frequencyof algternating current .

Answer 8

-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 !

Question 9

What are electrical supplies in the Uk connected to ?

Answer 9

-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 .

Question 10

What is the brown wire

Answer 10

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 .

Question 11

What is the Blue wire - neutral .

Answer 11

It completes the circuit , Potential difffernece =0V compred to the live wire .

Question 12

What is the green / yellow striped wire .

Answer 12

Earth wire this is a safety wire that stops the appliance beocmign live .

Question 13

What is the neutral wire .

Answer 13

complestes the circuit .
-the potential difference 0V compared to the live wire .

Question 14

-What is the green /yellow striped wire .

Answer 14

Earth wire - this is a safety wire that stops the appliance from becoming live

Question 15

Check the sheet what is it and what dpes ot swp

Answer 15

-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 .

Question 16

How could the live wire be extreemly dangeours ?

Answer 16

-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 .

Question 17

What about p.d of Earth ?

Answer 17

-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 .

Question 18

How can ppliances with metal cases be very dangerous ?

Answer 18

-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 .

Question 19

solution to METAL cases ?

Answer 19

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 .

Question 20

In exam , what are the only energy transfwrs we need to know ?

Answer 20

-Kinetic energy and thermla neergy .

Question 21

What does a BLENDER and a FAN TRANSFER ?

Answer 21

-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 .

Question 22

What does an IRON and KETTLE transfer ?

Answer 22

Transfers ELECTRICAL ENERGY into THERMAL ENERGY .
-As both appliances are designed to get hot .

Question 23

What does a HAIR DRYER AND A WASHIGN MACHIEN transfer ?

Answer 23

They transfer eectricl ennergy into kinetic energy OF ELECTRICAL MOTORS and THERMAL ENERGY.

Question 24

What is power ?

Answer 24

-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 .

Question 25

-How can we calculagte hte pwoer of a componenet ?

Answer 25

-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

Question 26

Do the quiestion oon the sheet

Answer 26

.

Question 27

How do we work out the pwoer of a componeent but we only know RESISTANCE not p.d ?

Answer 27

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

Question 28

Electrical charge in circuits ?

Answer 28

-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 .

Question 29

Equariton of elecrricla charge ?

Answer 29

Q =I*T
QIT trinagle
Charge flow (c)=Icurrent (a) *Ttime (s)
DO THE QUESTION ON SHEET .

Question 30

HOW DO YOU CALCULATE ENERGY TRANSFERS IN COMPONENTS ?

Answer 30

E =Q*V
Eneegyr transferred () *V potenitl difference (v)
DO THE QUESTION ON THE SHEET .

Question 31

-WHEN CHARGE FLOWS THORUHG A RESISOTR , ENERGY IS TRANSFERRED OT THE RESISTOR , SO THE RESISTOR BECOMES HOTTER .

Answer 31

./…

Question 32

What is efficency ?

Answer 32

-Efficencu is used to tell us what fraction of the energyw e put into an appliace is transferred into useful forms of enrgy .

Question 33

HOW TO CALCULATE EFFICENCY ?

Answer 33

Usefuloutput /total input *100
Cannoot get an efficency more than a hudnred percern or more than one SO OTHERWISE IT WORNG .

Question 34

How ot workout energy transferred by an appliacne ?

Answer 34

Energy = pwoer time
E=pt
DO practice question
CONVERT TO KJ WHERE POSSIBLE .