2.4 Energy transfer Flashcards
2.4.1 Power
2 formulas to calculate power
power = voltage x current
power = current x current x resistance
current x current = current squared
2.4.2 Energy transfers in everyday appliances
what does the amount of energy of an appliance depend on?
- how long the appliance is switched on for
- the power of the appliance
2.4.2 Energy transfers in everyday appliances
2 formulas for energy transferred
energy transferred = power × time
E = P t
energy transferred = charge flow × potential difference
E = Q V
energy transferred, in joules, J
power, in watts, W
time, in seconds, s
charge flow, in coulombs, C
2.4.2 Energy transfers in everyday appliances
How is the power of a circuit device related to the voltage across it?
- the greater the power, the greater the potential difference
2.4.2 Energy transfers in everyday appliances
How is the power of a circuit device related to the current?
- the greater the power, the greater the current through it
2.4.2 The National Grid
What is the definition of the National Grid?
The National Grid is a system of cables and transformers linking power stations to consumers
2.4.2 The National Grid
What do step-up transformers do?
They increase the voltage from the power staton to the transmission cable.
Increased voltage = decreased current
2.4.2 The National Grid
What do step-down transformers do?
They are used to decrease the voltage to a much lower value (230V) for domestic use in homes.
Decreased voltage = increased current
2.4.2 The National Grid
Why are transformers used in the National Grid?
- Electric current generates heat as it moved through electrical wires
- If electricity is transmitted at a** very high potential difference and low current** this means less energy is wasted as heat making the whole system more efficient.
2.4.2 The National Grid
What does the step up transformer look like?
On the left hand side of the square ring, there are less primary coils.
On the right hand side of the square ring, there are more secondary coils
In the middle gap of the square ring, there is a magnetic field.
2.4.2 The National Grid
What does a step-down transformer look like?
On the left hand side of the square ring, there are more primary coils.
On the right hand side of the square ring, there are less secondary coils
In the middle gap of the square ring, there is a magnetic field.
2.4.2 The National Grid
Formula of coils
voltage x current (in primary coil) = voltage x current (in secondary coil)