P5

Question 1

state the main sources of electricity + the type of electricity they generate

Answer 1

Most electricity is generated with steam turbines using fossil fuels,

Question 2

whats d.c electricity

Answer 2

d.c electricity = direct current ,an electric current flowing in one direction only.

Question 3

whats a.c

Answer 3

alternating current

an electric current that reverses its direction many times a second at regular intervals

Question 4

whats the frequency of mains electricity

Answer 4

The two commonly used frequencies are 50 Hz and 60 Hz

Question 5

how many times does mains electricity change direction every second ?

Answer 5

the direction of the current and voltage changes 100 times per second.

Question 6

whats the potential difference of mains electricity

Answer 6

The wire covered in brown plastic is the live wire. This carries the 230 V alternating potential difference from the power supply. The wire covered in blue plastic is the neutral wire and this completes the circuit from the appliance back to the supply.

Question 7

oscilloscope

Answer 7

electronic test instrument that graphically displays varying signal voltages

Question 8

label the plug

Answer 8

earth wire - striped goes to the top
neutral wire - fold over blue wire
live wire - brown , the one thats on the right

all are copper wires which are good conductors

Question 9

label the rest of the plug

Answer 9

the thing that looks like the battery on the side = the fuse

the thinf at the bottom of all the wires is the cable grip

the wire/lead is called the outer insulation

case is plastic - plastics a good insulator

Question 10

what links frequency and period

Answer 10

frequency = 1
———————
periodic time

periodic time = 1
————————
frequency

Question 11

5 safety rules for mains electricity

Answer 11

no water near 
check for damages wires + cables
unplug if not using 
dont block plug sockets 
turn it off at wall when plugging in

Question 12

what material is the cable insulator made from and why

Answer 12

Synthetic rubber compounds are used widely for insulation and sheathing of cables for flexible and for heavy duty applications. Many variations are possible, with conductor temperature ratings from 60°C to 180°C, as well as resistance to oil, ozone and ultra-violet radiation depending on the formulation.

Question 13

whats the role of an earth wire ?

Answer 13

Earthing is used to protect you from an electric shock.

Question 14

what does the neutral wire do

Answer 14

returns the electricity to the generator after it has passed through

Question 15

what does the live wire do

Answer 15

connected directly to the generator - carries current at very high voltage

Question 16

what material is used for the 3 pins on a plug and why

Answer 16

Brass material is resistant to overheating. It is very important for pins used in electric plugs to resist heat as overheating may cause fire.

Question 17

how does the fuse protect

Answer 17

The fuse breaks the circuit if a fault in an appliance causes too much current to flow. This protects the wiring and the appliance if something goes wrong.

Question 18

how does a circuit breaker work

Answer 18

i ts basic function is to interrupt current flow after protective relays detect a fault.

Question 19

2 advantages of a circuit breaker over a fuse

Answer 19

CB = quicker , more reliable

Question 20

whats an rccb

Answer 20

Residual Current Circuit Breaker

Question 21

purpose of an rccb

Answer 21

its an electrical wiring device that disconnects the circuit whenever there is leakage of current flow through the Human body or the current is not balanced between the phaseconductor.

Question 22

definition of power and its unit

Answer 22

power is the amount of energy transferred or converted per unit time (watts)

Question 23

power equation

Answer 23

power = potential difference × current

Question 24

energy transferred

Answer 24

watts / 1000 = the kW