topic 2 - electricity: energy transfers Flashcards
What is the equation which links power, potential difference and current?
power = potential difference x current
What is the symbol for power?
P
What is the symbol for potential difference?
V
What is the symbol for current?
I
What is the equation which links power, current and resistance?
power = (current)2 x resistance
What is the symbol for resistance?
R
What is the power of an appliance?
The amount of energy that it transfers per second.
What are the units for power?
watts (W)
What are the units for potential difference?
volts (V)
What are the units for current?
amps (A)
What are the units for resistance?
ohms (Ω)
What two factors does the total energy transferred by an appliance depend on?
How long the appliance is on for and it’s power.
Will a circuit with high current and potential difference have a high or low power?
High.
What are everyday electrical appliances designed to bring about?
Energy transfers.
How does a kettle transfer energy from ac mains to the heating device?
Kettles transfer energy electrically from the mains ac supply to the thermal energy store of the heating element inside the kettle.
How is energy transferred from the battery of a handheld fan to its electric motor?
Energy is transferred electrically from the battery of a handheld fan to the kinetic energy store of the fan’s motor.
What has to flow in a circuit to allow work to be done?
Charge.
What is the equation that links energy transferred, power and time (equation for energy transferred by electrical work)?
energy transferred = power x time
What is the equation that links energy transferred, charge flow and potential difference?
energy transferred = charge flow x potential difference
What is the symbol for energy transferred?
E
What is the symbol for power?
P
What is the symbol for time?
t
What is the symbol for charge flow?
Q
What is the symbol for potential difference?
V
What are the units for energy transferred?
joules (J)
What are the units for power?
watts (W)
What are the units for time?
seconds (s)
What are the units for charge flow?
coulombs (C)
What are the units for potential difference?
volts (V)
What is potential difference?
Energy transferred per charge passed.
Will a battery with a higher potential difference supply more or less energy to the circuit per coulomb of charge?
More energy.
What is the power rating of an appliance?
The maximum safe power that an appliance can operate at.
The power rating of an appliance tells you the _______ amount of ______ transferred between stores ___ ______ when the appliance is on.
maximum, energy, per second
Why do power ratings help customers choose between models of an appliance?
The lower the power rating, the less electricity an appliance uses in a given time and so the cheaper it is to run.
Why does a high power rating not necessarily mean that an appliance transfers more energy usefully?
An appliance may be more powerful than another, but less efficient, meaning that it might transfer the same amount of energy (or less) to the useful stores.
What is the National Grid?
A system of cables and transformers linking power stations to consumers.
What type of power is transferred from power stations to consumers using the National Grid?
Electrical power.
Why do power stations often run well below their maximum output?
So there is spare capacity to cope with an unexpected spike in demand.
Why is the National Grid system an efficient way to transfer energy?
It uses a high pd (400,000 V) and a low current which is cheaper and decreases the energy lost by heatint the wires and the surroundings.
What is the purpose of step-up transformers in the National Grid?
Increase the potential difference from the power station to the transmission cables.
What is the purpose of a step-down transformer in the National Grid?
Decrease, to a much lower value, the potential difference to make the power suitable for domestic use.
