Unit D Section 3.3 Flashcards
Power:
Power is the rate at which a device converts energy
The unit of power is the watt (W)
a watt is equal to how many jules:
A watt is equal to one joule per second.
the faster a device converts energy,,,,,,
The faster a device converts energy, the greater its power rating.
Calculation to find the power:
P = I V (watts = amperes x volts)
Power modelled by water:
The power of a waterfall is equal to the amount of water flowing times the difference in potential energy between the top of the falls and the bottom= this like current flow times potential drop in a circuit.
What do most small appliances in our home have a power rating of?
Most small appliances in your home have a power rating of 1500 W or less.
An electric stove might have a power rating of 7000 W, while the rating for a calculator could be only 0.4 mW.
How can you find out the energy?
You can find the amount of energy converted by multiplying this rate by the length of time the device operates.
The energy consumption of an electrical device is its input power multiplied by the time the device is used: E = P x t. Recall that energy is measured in joules (watts x seconds)
energy calculation is the same, except that hours are substituted for seconds, and kilowatts (kW) are substituted for watts.
What is kilowatt hour?
the kilowatt hour is often used as a unit for energy.
kilowatt hour : seconds are substituted for time and kilowatts or substitutes for watts/
How does a company count the amount of electricity of pay for?
Electricity meters measure the energy used in kilowatt hours. The electric company then bills you for every kilowatt hour used.
What is efficiency of a device?
The efficiency of a device is the ratio of the useful energy that comes out of a device to the total energy that went in.
How can a device be efficient?
The more input energy that a device converts into useable output energy, the more efficient the device is.
Are florescent bulbs more effiecient or incandescent?
Although fluorescent tubes also produce more heat than light, they transform about 20% of their input energy into light.Thus, they require much less energy to produce the same amount of light as incandescent bulbs.
Arc-discharge lamps are even more efficient. they produce light by passing an electric arc through a vapour of a metal such as mercury or sodium. ( produces ultraviolet light (UV))
Are hybrid gasoline cars more efficient or just gasoline cars?
Hybrid gasoline-electric cars can be twice as efficient as gasoline-powered vehicles.
The hybrid uses a smaller gasoline engine and an electric motor that provides extra power when needed.
Law of conservation energy:
- Energy cannot be created or destroyed or appear or disappear.
- One form of energy can only be transformed to another form
- Whenever energy is transformed , there is always loss of some useful energy
Energy dissipation:
Energy dissipation is wasted energy which is the energy that is not useful.
we usually find that the output energy of a device or system is smaller than the input energy.
example, when you heat a beaker of water on a hot plate, the hot plate transfers some heat to the surrounding air instead of to the water= radiates heat to other objects.
