P5 Flashcards
How are devices that use plugs and devices that use batteries different (Batteries use DC current)
-Battery devices can be used anywhere but plugged devices must be used near a plug
-Batteries transfer energy from chemical ptotential by electric current, plugs directly supply electrical energy
How aee devices that use plugs and devices that use batteries the same?c (plugges devices use AC CURRENT)
- both transfer energy to electrical devices
- both must be connected to the device
AC means
Alternating current
DC means
Direct current
Direct current means
The current flows in one direction only
Alternating current means
The current constantlg changes direction, how often is called frequency
DC examples
Cells, batteries
AC examples
Mains supply, power socket
DC current on a graph maintains a
Constant voltage due to the singke direction current flow
AC current on a graph constantly
Reverses its voltage (up and down) due to the current constsntly changing direction (freauency)(Hz)
Mains electricity
An alternating current
In the UK mains electricity is about
230 V
In the Uk mains electricity has a frequency of
50Hz
Transmitting electricity at a high voltage reduces power loss, making
The system more efficient
Step-up transformer
Increases the voltage, but decreases the current
Step- down transformer
Decreases the voltage, increases the current
Power station function
Burns fuel - heats water - steam - turn turbine - turn generator - generate electricity
Electricity is dustributed via the
National grid
The national grid is a gaint susten if
Cables and transformers that civer the UK and connects power stations to consumers
Disadvantages of underground cables
- very expensive (miles and miles of cable)
- lots of digging
- maintenance is hard, must dig them up
- cables get hot, hard too cool (underground). Must be thicker
- would need to clearky mark where they are in order for no one to dig them up.
What are the ads and dis of overhead cables?
- relativelt cheap to link between tall towers
- easy access to maintain cables
- open to air cooling of cables
Dis:
- ugly, ruin landscapes
- vulnerable to weather
- must cut across large amount of land
How do fuses work?
-The fuse breaks the circuit if a fault in an appliance causes too much current flow.
-This protects the wiring and the appliance if something goes wrong.
-The fuse contains a piece of wire which melts easily.
-If the current going through the fuse is too great, the wire heats up until it melts and breaks the circuit.
Fuses in plugs are made in standard ratings. The most common are:
3 A, 5 A and 13 A.
-The fuse should be rated at a slightly higher current than the device needs:
• If the device works at 3 A, use a 5 A fuse
• If the device works at 10 A, use a 13 A fuse
Residual current circuit breakers, RCCBs, protect some circuits. They detect a difference
in the current between the live and neutral wires. RCCBs work much faster than fuses do.
Live wire
- brown
- provides the alternating difference from the mains supply.
Nuetral wire
- Blue
- nuetral wire completes the circuit.
- when the appliance is operating normally, current flows through the live and nuetral wire - around 0 V
Power, energy transferred, time
Energy (J’) = power (W) x time (s)
E =. Pt
Earth wire
- green and yellow
- for protecting the wiring
- and for safety
- stops the appliance casing from becoming live
- doesn’t usually carry a current - only when there’s a fault, at 0 V
Watts (W) = Joules per second (J/s)
1W = 1 J/s
Power, potential difference, current
Power (W) = potential difference (V) x Current (A)
P = V X I
Power, current, resistance
P = I (squared) X Resistance
Current, coulomb, time
Current (A) = Coulomb (charge flow, C) DIVIDED BY time (s)
A (amps) = Coulombs per second (C/s)
1 A = 1 C/s
Energy transferred, charge flow, potential difference
Energy transferred (j) = charge flow(C) X Potential difference( (V)
