electricity Flashcards
what is current
The rate of flow of charge
What equation links charge, current and time?
charge = current x time (Q = I x t)
What is potential difference?
The energy transferred per coulomb of charge between two points.
Where should an ammeter and voltmeter be placed in a circuit?
Ammeter in series with the component
Voltmeter in parallel with the component
What is resistance?
Resistance makes it harder for the current to flow.
What equation links current, potential difference and resistance?
potential difference = current x resistance
V = I x R
What is the relationship between pd and current through a fixed resistor?
They are directly proportional.
Why does the resistance through a filament lamp increase as the pd increases?
As pd increases, current increases.
When current increases, more electrons flow.
When electrons flow, they collide with ions and other electrons.
This transfers energy to the ions, increasing the temperature.
As the temperature increases, the ions vibrate more.
This causes more collisions between the electrons and the ions, making it harder for the electrons to flow.
What is a thermistor?
A resistor that decreases in resistance as the temperature increases.
What is an LDR?
A resistor that decreases in resistance as the light intensity increases.
Compare series and parallel circuits.
Series circuits
Current same at every point
pd shared between components
(Component with bigger resistance has bigger share of pd)
Total resistance is the sum of the individual resistors
Parallel circuits
Current shared between branches
(Branch with less resistance has bigger share of current)
pd across each branch is the same as the pd across the cells
Total resistance is less than the smallest resistor
What is a diode?
A component that only allows current to flow in one direction because the resistance is so high in the opposite direction
What equation links charge, energy transferred and potential difference?
energy = charge x pd
E = Q x V
What equation links current, potential difference and power?
power = current x pd
P = I x V
What equation links current, power and resistance?
power = current2 x resistance
P = I2 x R
What is the difference between a direct current and an alternating current?
Direct current flows in one direction only
Alternating current constantly changing direction
What is the voltage and frequency of UK mains electricity?
230V, 50Hz
What colour are each of the three wires in a plug?
Live wire is brown
Neutral wire is blue
Earth wire is yellow and green
What is the role of the three wires in the plug?
Live wire brings electricity into the appliance at 230V
Neutral wire completes the circuit, electricity at 0V
Earth wire takes current away from the appliance if there is a fault.
How do the earth wire and fuse work together?
Earth wire has low resistance so in event of the live wire becoming loose, current surges down the earth wire.
This blows the fuse, breaking the circuit.
This prevents appliance fires
Why do some appliances only have two wires?
Appliances with a plastic case (double insulated) don’t need an earth wire because the case doesn’t conduct electricity so can’t become live.
What is the National Grid?
The network of power lines connecting the power stations to homes and industry.
Describe the role of step-up transformers in the National Grid.
Step-up transformers increase the voltage
This decreases the current flowing
This reduces energy losses due to heating of the power lines
Increasing the efficiency
Describe the role of step- down transformers in the National Grid.
Step-down transformers decrease the voltage
Making it safer to use in our homes
