P5 - Electricity In The Home Flashcards
What are the two types of electricity supply?
Alternating current (ac) and Direct current (dc)
What is alternating current?
Current that is constantly changing direction
What produces alternating currents?
Alternating voltages
Is the electricity in our home ac or dc supply?
AC
What voltage is the AC supply in our homes?
230V
What frequency of the AC supply in our homes?
50Hz
Where can dc supply be found?
Cells and batteries
What is direct current?
Current that is always flowing in one direction
What is direct current created by?
Direct voltage
What colour is the live wire?
Brown
What colour is the neutral wire?
Blue
What colour is the earth wire?
Green and yellow
What does the live wire do?
Provides the alternating potential difference at 230V from the mains supply
What does the neutral wire do?
It just completes the circuit and is at 0V
What does the earth wire do?
For protecting the wiring and for safety. Its at 0V
What is the voltage or a normal human being?
0V
What is the equation that links energy transferred, charge flow and potential difference?
E = QV
What is the equation linking power, potential difference and current?
P = VI
What is the equation to find out power without knowing the potential difference?
P = I*2 x R
What does the national grid do?
Transfers electrical power from power stations from anywhere on the grid to places anywhere that need it
What do you need in a circuit to transmit huge amount of power?
A high potential difference or a high current
What is the problem of a high current?
Energy will be lost as it is transferred to thermal energy to the surroundings
What is the national grid exactly?
A huge network of wires that covers Britain.
It generates electricity from power stations to homes everywhere
.
When would a demand for electricity increase?
When its dark or cold outside
When people come home from work or school
A popular event is on TV
What is the structure of any transformer?
A primary coil and a secondary coil joined together with an iron ore
What is an equation to express the power of a primary coil in a transformer?
Power = potential difference x current
How efficient are transformers?
Nearly 100% efficient
Because transformers are nearly 100% efficient, whats the relation between the primary and secondary coil?
Power in primary = power in secondary
What is static electricity?
The build up of charge on an objects surface
If two normal objects, like a bag and a hat, are rubbed together, what happens to the electrons?
The friction between them causes electrons to be rubbed off one of them (like the hat) and on to the other one (like the bag)
If two conducting materials, like metals , are rubbed together, what happens to the electrons?
The electrons just flow back and forth
This means no charge ever builds up
If two insulating materials, like a cloth and a polystyrene rod , are rubbed together, what happens to the electrons?
The electrons cant flow back so the transfer caused by the friction gives a
POSITIVE static charge on the material that lost the electrons
and a NEGATIVE static charge on the material that gained the electrons
In static electricity which electrons are being transferred?
Only the negative electrons are being transferred
What happens when an object keeps on gaining negative electrons?
More electrons transferred and the size of the charge increases leads to potential difference between the charged material and the earh
What happens when the potential difference between the charged object and earth object is large enough?
Electrons can jump across the gap
We see this as a spark
What are the three ‘fields’?
Electric fields
Gravitational fields
Magnetic fields
How can you draw the electrical field around an object?
Draw electric field lines
How do electrical field lines show the electric field?
Arrows facing out are positive
Arrows facing in are negative
The close the arrows are, the stronger the field
What happens in the interaction between electric fields and air
A strong electric field can cause surrounding air particles to lose electrons and become positively charged
Explain why a spark jumps between a negatively charged rod and an earthed conductor.
The earthed conductor gains the negatively electrons from the rod very easily - creating a strong field between them
As this field gets stronger, air particles break, allowing electrons to jump across the air
We see this as a spark
A negatively charged plastic rod is placed on a scale.
Another charged plastic rod is hovered over the rod and the mass increases
Explain why.
There is an additional downwards forces on 5e balance so the mass increases
This is because both rods are negatively charged and repel
