Power and Energy transfers Flashcards
(17 cards)
Why does a moving charge transfer energy?
the charge does work against the resistance of the circuit.
work done = energy transferred
What are everyday electrical appliances designed to do?
Everyday electrical appliances are designed to bring about energy transfers.
What does the amount of energy an appliance transfers depend on?
The amount of energy an appliance transfers depends on how long the appliance is switched on for and the power of the appliance.
What is the power f an appliance?
the energy it transfers per second - the more energy it transfers in a given time, the higher its power.
How is work done in a kettle?
Kettles transfer energy electrically from the mains ac supply to the thermal energy store of the heating element inside the kettle.
How is work done in a handheld fan.
Energy is transferred electrically from the battery of a handheld fan to the kinetic energy store of the fan’s motor.
How is energy transferred in a torch?
In a torch, the energy stored in the battery is used to heat up the filament of the bulb.
How is energy transferred in a hoover?
In a vacuum cleaner,
energy is usefully transferred from the power station to make the motor spin. Some of the energy is transferred less usefully into the room through sound and heat.
What is the equation involving energy transferred, power and time?
Energy transferred (J) = Power (W) x Time (s)
E=Pt
What is the power rating of an appliance?
the max safe power they can operate at.
What does the power rating tell you?
the max amount of energy transferred between stores per second when the appliance is in use.
What does a lower power rating mean for the price to run an appliance?
Lower power rating = less electricity used in a given time = cheaper to run
more power doesn’t mean more efficient
What happens when an electrical charge goes through a change in pd?
energy is transferred (work is done). Energy is supplied to the charge at the power source to raise it through a potential. The charge gives up this energy when it ‘falls’ thru any potential drop in components elsewhere in the circuit
What is the formula connecting energy transferred, charge flow and pd?
Energy transferred (J) = Charge flow (C) x Pd (V)
E = QV
How can you find the power using the current and Pd?
Power (W) = Pd (V) x Current (A)
P = VI
How can you find the power if u don’t know the pd?
P = I (squared) x R
