P2 Electricity Flashcards
What is alternating current?
Electric current in a circuit that repeatedly changes direction
What is direct current?
Electric current in a circuit that flows in one direction only
What is power?
The energy transformed or transferred per second
What is the unit for power?
Watts, W
What is efficiency?
Useful energy transferred by a device / total energy supplied to a device
What is potential difference?
A measure of the work done or energy transferred between 2 points in an electrical circuit
What is the unit for potential difference?
Volts, V
What is the national grid?
The network of cables and transformers used to transfer electricity from electricity producers to electricity consumers
What is the unit for energy?
Joules, J
What are the 3 equations to calculate power?
- Power = Energy / Time (P = E / T) - PET
- Power = Current x Voltage (P = I x V) - Penguins in Vegas
- Power = Current^2 x Resistance (P = I^2 x R) - Penguins in a square room
What are the 2 equations to calculate energy?
- Energy = Power x Time (E = P x T)
- Energy = Charge x Voltage (E = Q x V) - Every Queen Vacuums
What are the 2 equations to calculate efficiency?
- (useful energy out / total energy in) x 100
- (useful power out / total power in) x 100
What colour is the live wire?
Brown
What is the function of the live wire?
Carries a current that alternates between negative and positive voltage - current flows in through
What colour is the earth wire?
Green/yellow
What is the function of the earth wire?
A safety feature that is needed to earth electrical appliances with metal casing. This makes it safer to touch an appliance if it develops a fault - only has current if there is a fault
What is the function of the neutral wire?
Completes the circuit. Kept at 0 voltage by the electricity company - current flows out through
What colour is the neutral wire?
Blue
What is the function of the fuse in a plug?
Can melt (blow) if too much current flows through - breaks the circuit
What type of supply is mains electricity?
a.c. supply
What is the voltage of mains electricity?
230V
What is the frequency of mains electricity?
50Hz
What does the frequency of mains electricity mean (50Hz)?
That it changes direction and back again 50 times a second (analogue signal graph)
What does directly proportional mean?
Double one, doubles the other
What does inversely proportional mean?
Double one, halves the other
What does a diode do?
Only lets current flow one direction - very high resistance in the ‘wrong direction’
What is current measured in?
Amps, A
What is charge measured in?
Coulombs, C
What is potential difference?
Difference in energy between 2 points
What is the function of a thermistor?
Changes resistance with temperature - higher temp = lower resistance
What is the function of a variable resistor?
We can manually change the resistance
What is the function of a fixed value resistor?
Always has the same resistance value
What is resistance?
How hard it is for current to flow
What are the 2 types of circuit?
Series and parallel
Explain current in a series circuit:
Current same at every point in a series circuit
Explain current in a parallel circuit:
Total current in a parallel circuit = sum of currents through the separate components
Explain p.d. in a series circuit:
Total p.d. of power supply is shared between the components
Explain p.d. in a parallel circuit:
p.d across each component is the same
Explain resistance in a series circuit:
More resistors, greater the resistance. Total resistance of 2 components = sum of resistance of each component (R^total = R^1 + R^2)
Explain resistance in a parallel circuit:
More resistors, lower resistance. Total resistance of 2 resistors is less than resistance of smallest individual resistor
What is the equation for charge?
Charge = current x time (Q = I x T)- QUIT
What is the equation for potential difference?
p.d. = current x resistance (V = I x R) - Very Important Rabbit
What is the equation for power?
Power = p.d. x current (P = I x V) - Penguins In Vegas
What is the equation for energy transferred?
Energy transferred = power x time (E = P x T)
What is electric current?
Flow of electric charge
What is resistance caused by?
Anything which opposes the flow of electric charge
What is charge?
Anything charged which is able to move within a circuit - electrons or ions
What is a series circuit?
A circuit with only one route for charge to take
What is a parallel circuit?
A circuit with more than one route for charge to take
Describe the V/I graph of a filament lamp:
Resistance is not constant - as temp increases, resistance increases as ions vibrate more increasing collisions with electrons
Describe the V/I graph of a fixed resistor:
Resistance is constant. Current and p.d. are directly proportional
Describe the V/I graph of a diode/LED:
Current flows one-way. High resistance in reverse direction
What is the function of a step-up transformer?
Increases p.d. for transmisson across power cables - less current, less heat lost
What is the function of a step-down transformer?
Reduces the p.d. from the cables to 230V for use by consumers
What power supply does batteries/cells use?
d.c. supply
Where do electric fields exist?
Around all objects
Electric fields - what does it mean if field lines are closer together?
Pulling force is stronger
Where do field lines point?
Positive to negative charge
What is the equation for density?
Density = mass (kg) / volume (m^3)
What is density?
The mass of a substance per unit volume
Are smaller objects more/less dense?
More dense
What happens when 2 insulators are rubbed together?
They become charged
What does friction force cause?
Electrons to be transferred between insulators
Is the total no. of protons/electrons constant or alternating?
Constant
Do oppositely charged objects attract/repel?
Attract
Do objects with the same charge attract/repel?
Repel
What is charging by induction?
When a negative object is moved towards a negative object, electrons are repelled to the other side - closest surface becomes positively charged. Works same other way, leaving opposite surface negatively charged
