P2.4 Flashcards
What items use a direct current?
~ Phones
~ Laptops
~ Torches
What are the two types of electric current?
~ Direct current (D.C.)
~ Alternating current (A.C.)
What type of current is supplied by the mains?
Alternating current
What does alternating current do?
~ Repeatedly reverses direction
~ So flows one way and then the opposite way in cycles
~ The number of cycles per second is called the frequency
What is the frequency of alternating current in the U.K.?
50 Hz (50 cycles per second)
What is the voltage of alternating current in the U.K.?
230 V
What is an oscilloscope?
A machine that shows readings on potential difference and current
What is a period in alternating current?
The time taken for 1 cycle (on a graph the line curving above and then below the line)
What is a 3 core cable?
A cable with 3 copper wires (red, green + yellow stripes, blue)
What is a 2 core cable?
A cable with 2 copper wires (blue and brown)
How is a plug made safe?
~ Tough case + cable made of plastic (good insulator)
~ Cable/cord grip holds cable in place
~ Fuse which will melt if the current gets too high
What colour is the live wire in a plug?
Brown
What colour is the neutral wire in a plug?
Blue
What colour is the earth wire in a plug?
Green + yellow stripes
What appliances do 2 core cables connect to?
Double insulated appliances like hairdryers (those with a non-metal outer casing)
What appliances do 3 core cables connect to?
Appliances with metal casing like kettles
How are we protected from electric shocks from the live wire in a 2 cable
There are two cases of insulating plastic between the live wire and the outside of the appliance
How can the earth wire prevent the metal casing of an appliance causing electric shocks by the live wire becoming loose and touching the metal case?
~ It is connected to the casing
~ The current would be directed through the earth wire, back to the plug and into the ground
~ The fuse will blow quickly
What does a RCCB do?
They switch off the current in dangerous situations
How do a RCCB work?
Detects a difference in current between the live wire and the neutral wire
Why is using an RCCB better than a fuse?
~ Faster
~ Can be re-set
What sort of appliances have no earth wire?
Double insulted ones
When does a resistor get hot?
When an electrical charge flows through it
What happens to a wire carrying a current?
It gets warmer
Why do bigger appliances have thicker cables?
To reduce the heat produced through the wire
What is the problem with filament lamps?
Gets very hot which makes it glow, but the heat energy is wasted
What is good about Compact Fluorescent Lamps?
~ Produce less heat
~ So more efficient and less wasteful
