73496
Electrical
energy
- Power
- Energy supplied to an electrical device
per second is the power supplied to it
- We say that the more
powerful a device, the faster
the rate at which it transforms
energy
- Power (in watts, W) = rate of
transfer of energy
- = energy transferred (in joules J)
_________________________________
time taken (in seconds, s)
- = energy transferred (in joules J)
_________________________________
time taken (in seconds, s)
- Power (in watts, W) = rate of
transfer of energy
- Measure the power of a device in
watts (W) or in kilowatts (kW)
- For any device: - the input energy is the
energy supplied to it - the output energy is
the useful energy per second transferred by it
- 1 watt is a rate of transfer
of energy of 1 joule per
second (J/s)
- 1kW device in an hour is 1
kilowatt-hour (kW h)
- 1kW device in an hour is 1
kilowatt-hour (kW h)
- 1 kilowatt 1000 watts
- 1 watt is a rate of transfer
of energy of 1 joule per
second (J/s)
- For any device: - the input energy is the
energy supplied to it - the output energy is
the useful energy per second transferred by it
- Energy transferred (kW h) = power of device (kW) x time in use (hours, h)
- We say that the more
powerful a device, the faster
the rate at which it transforms
energy
- a 2kW heater switched on for 4
hours uses 8kW h of electrical
energy
- When paying the electricity bill, we use this equation:
total cost = number of kW h used x cost per kW h
- When paying the electricity bill, we use this equation:
total cost = number of kW h used x cost per kW h
- Energy supplied to an electrical device
per second is the power supplied to it
- Electrical devices & energy
- When we use an electrical device,
some energy transformed is useful,
and the rest is wasted
- When we use an electrical device,
some energy transformed is useful,
and the rest is wasted
- National Grid
- we use step-up
transformers in power
stations and stepdown
transformers in sub-stations
near homes
- Step-up transformer
increases the votlage
- Step-down
transformer
decreases the
voltage
- The National Grid’s voltage is 132000 volts
plus, and power stations only produce electricity
at a voltage of 25000 volts. This is when we use
step-up transformers at power stations to step this
voltage up to the National Grid voltage, and
then we use step-down transformers at the
sub-stations near our homes to step the voltage
back down to 230 volts for homes and offices
- Some people constantly debate over whether
they should be built above or below ground. If
they are built above ground they are visible
and not aesthetically pleasing, but
campaigners for underground mains could be
argued with, because underground cables are
far more expensive, much more difficult to
repair and are extremely difficult to bury where
they cross canals, rivers and roads
- Some people constantly debate over whether
they should be built above or below ground. If
they are built above ground they are visible
and not aesthetically pleasing, but
campaigners for underground mains could be
argued with, because underground cables are
far more expensive, much more difficult to
repair and are extremely difficult to bury where
they cross canals, rivers and roads
- Step-up transformer
increases the votlage
- Electricity reaches our home
through the national grid
- we use step-up
transformers in power
stations and stepdown
transformers in sub-stations
near homes
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