Electric circuits Flashcards
What is the unit for resistance?
Ohms (Ω)
What is a series circuit?
A circuit with all components on a single loop only
What equation links energy transferred, charge flow, and potential difference?
Energy transferred = charge x potential difference
E = QV
What two things are needed for electric charge to flow in a circuit?
- A source of potential difference
- a closed circuit
What equation links potential difference, current, and resistance?
Potential difference = current x resistance
V = IR
What is the unit of current?
Amperes or amps (A)
What is the unit of electric charge?
Coulombs (C)
What two measurements need to be made to determine the resistance of a component?
The potential difference across the component, and the current through the component
What is the rule for potential difference in a parallel circuit?
The potential difference across each branch is the same
What is the rule for current in a series circuit?
The current is the same through each component and at each point in the circuit
What is the definition of electric current?
The rate of flow of charge
What is the rule for potential difference in a series circuit?
The sum of the potential differences across each component is equal to the potential difference of the power supply
What equation links charge flow, current, and time?
Charge flow = current x time
Q = It
What is the rule for current in a parallel circuit?
The total current through the whole circuit is the sum of the currents through each branch
What is true about the current at any point in a single closed loop?
It has the same value at any point
What is a parallel circuit?
A circuit with components on multiple loops
Definition of current
Rate of flow of charge
How does thickness of material affect resistance?
As thickness increases (+ length remains constant) more electrons can flow through the wire, so the current is higher + the resistance is therefore smaller
How does length affect resistance?
As the length increases (+ thickness is constant) there are more metal ions along the direction of current flow. This means that more collisions occur, so the resistance has increased
How does temperature affect resistance?
As temperature increases, the metal ions vibrate faster and with a greater amplitude. This means that the free electrons are more likely to collide with a metal ion, increasing the resistance.
What is meant by an alternating potential difference?
The direction of the potential difference changes
What is the job of the earth wire?
A safety feature to stop an appliance becoming live
What is a diode?
A device which allows current to flow in one direction only
What is the rule for current in a parallel circuit?
The total current through the whole circuit is the sum of the currents through each branch
For a given potential difference across a component, if the resistance increases what happens to the current?
It decreases
What is the job of the live wire?
Carries the alternating potential difference from the supply
Why does a diode only allow current to flow in one direction?
It has a very high resistance in the reverse direction
What colour is the insulation on a live wire?
Brown
Which wire has green and yellow striped insulation?
Earth
What two measurements need to be made to determine the resistance of a component?
The potential difference across the component, and the current through the component
Which wire has brown insulation?
Live
What is the potential of the live wire?
230 V
What two things are needed for electric charge to flow in a circuit?
A source of potential difference, a closed circuit
How does the resistance of an LDR vary with light intensity?
Resistance decreases as light intensity increases
What equation links power transferred, current, and resistance?
Power = (current)^2 x resistance
P = I^2 R
What is the potential of the neutral wire?
0 V
What happens to the resistance of a light bulb as the potential difference increases?
The resistance increases
How do you calculate the total resistance of a circuit?
Total resistance = potential difference across battery / current through battery
What is the definition of electric current?
The rate of flow of charge
What is a parallel circuit?
A circuit with components on multiple loops
What is the unit of electric charge?
Coulombs (C)
How does the resistance of a thermistor vary with temperature?
Resistance decreases as temperature increases
What is the rule for potential difference in a series circuit?
The sum of the potential differences across each component is equal to the potential difference of the power supply
What is the potential of the earth wire?
0 V
What is an ohmic conductor?
One where the current is directly proportional to the potential difference, meaning the resistance remains constant
What equation links energy transferred, charge flow, and potential difference?
Energy transferred = charge x potential difference
E = QV
Why it is dangerous to provide any connection between the live wire and earth?
A large current will flow. If this passes through a person, they will be electrocuted.
They can suffer severe burns and their heart can stop
What is the rule for current in a series circuit?
The current is the same through each component and at each point in the circuit
What colour is the insulation on the earth wire?
Yellow and green stripes
What equation links potential difference, current, and resistance?
Potential difference = current x resistance
V = IR
What is the rule for potential difference in a parallel circuit?
The potential difference across each branch is the same
What is meant by a direct potential difference?
The direction of the potential difference is constant
What is the National Grid?
A system of cables and transformers linking power stations to consumers
What is the rule for total resistance in a parallel circuit?
The total resistance is less than the resistance of the smallest individual resistor
What equation links power transferred, current, and potential difference?
Power = current x potential difference
P = IV
What colour is the insulation on a neutral wire?
Blue
What is the job of the neutral wire?
Completes the circuit and returns to the power station
How does an earth wire stop an appliance becoming live?
If a fault occurs, a large current is drawn, which melts the fuse and disconnects the appliance from the mains
What is meant by an alternating current?
The charges oscillate
Which wire has blue insulation?
Neutral
Where should a fuse be placed in a plug?
By the pin for the live wire
What is the unit for current?
Amperes or amps (A)
What is the unit for resistance?
Ohms (Ω)
What is true about the current at any point in a single closed loop?
It has the same value at any point
Why does the resistance of a light bulb increase as the potential difference increases?
The current increases the temperature of the filament. Free electrons collide with the metal ions, making them vibrate with a greater amplitude
Why are step down transformers used on the national grid?
To reduce the potential difference to safer values for consumers
Why does the total resistance increase when a resistor is added in series?
The battery potential difference is now shared across another resistor, meaning the current in the circuit is reduced
What is the frequency of the UK mains electricity?
50 Hz
What equation links charge flow, current, and time?
Charge flow = current x time
Q = It
Why does the total resistance decrease when a resistor is added in parallel?
The potential difference across each resistor is the same, meaning there is another path for current, meaning the current in the circuit increases
What is meant by a direct current?
The charges flow in a single direction
What is the rule for two resistors in series?
The total resistance is the sum of the resistance of each resistor
RT = R1 + R2
What is a series circuit?
A circuit with all components on a single loop only
Why can a live wire be dangerous even when a switch in the mains circuit is open?
The live wire is still at 230 V if plugged in. If the insulation is damaged and the live wire is exposed, someone touching the wire will provide a connection to earth and they can be electrocuted
How can a thermistor be used in a sensing circuit?
Put it in series with a fixed resistor and a source of potential difference
What is the potential difference of the UK mains electricity?
230V
The resistance of a piece of wire with a constant thickness is ___ ___ to the length of the wire if the temperature remains constant
directly proportional
Why are step up transformers used on the national grid?
Stepping up the potential difference decreases the current in the transmission cables, decreasing the rate at which the cables are heated by current and increasing efficiency
