P2 Electricity random revision (pages 179-189) Flashcards
What is the flow of electrical charge also known as?
Electric Current
What will happen to the current through a component if its resistance decreases while the potential difference across it stays the same?
The current will increase
What is potential difference measured in?
Volts
What quantity is measured in ohms?
Resistance
The size of an electric current is equal to the rate of flow of what?
Electrical charge
Complete the equation using time and current. Charge flow = ?
Charge flow = current x time
What component does this circuit symbol represent?
A variable resistor
Complete the equation using curent and resistance. Potendial difference = ?
Potential difference = current x resistance
True of false? The resistance of an ohmic conductor remains constant as the current through the conductor is increased at a constant temperature?
True
Why does current only flow through a diode in one direction?
Because diodes have a very high resistance in the reverse direction
Name the component whose resistance changes with light intensity?
A light dependent resistor (of LDR)
Give one application of an LDR?
E.g. automatic night lights/burglar detectors
Describe how the resistance of a thermistor changes as the temperature decreases?
The resistance of the themistor increases
In what type of circuit is the potential difference of the power supply shared between the circuit components?
A series circuit
Name the electrical property tht is the same as all points in a series circuit?
Electric current
How can you calculate the total resistance of two components connected in series?
By adding their individual resistances together
A circuit contains a resistor. Explain, in terms of current and potential difference, why the total resistance of the circuit will increase if you add a resistor in series with the original resistor?
The resistors will share the potential difference of the power supply. So by adding the resistor, the potential difference across each resistor in the circuit will be lower. This means the current through each resistor will be lower. In a series circuit, the current is the same everywhere so the total current in the circuit will decrease. Therefore, the total resistance of the circuit will increase.
How would you connect two resistors i a circuit to make sure the potential difference across one resistor was always the same as the other?
You’d connect them in parallel with each other.
Whathapens to the current in a parallel circuit when it reaches a junction between two parallel branches?
The current splits between the branches.
Describe how to calculate the total current in a parallel circuit if you know the current in each of the parallel branches?
Add all the currents together
For two resistors connected in parallel, how does their total resistance compare to the resistance of the smallest of the two resistors?
Their total resistance will be smaller than the resistance of the smallest resistor.
Explain why connecting resistors in parallel decreases their total resistance?
In parallel, both resistors have the same potential difference across them as the power supply. This means the ‘pushing force’ making the current flow is the same as the source potential difference for each resistor added. By adding another loop, the current has more than one direction to go in, which means a greater total current can flow around the circuit. V = I x R, so an increase in current means a decrease in the total resistance of the circuit.
What type of current is supplied by the UK mains electricity supply?
Alternating current
What is the function of a neutral wire in an electrical appliance? What potential is this wire at?
The neutral wire completes the circuit with the live wire, meaning electricity can flow. It is around 0 V.
True or false? It is always dangerous to touch the live wire of a plugged‑in appliance, even if the plug socket is switched off (i.e. the switch is open). Explain your answer.
True. Even if a plug socket is turned off there is still a danger of an electric shock. A current isn’t flowing but there’s still a potential difference between you and the live wire. If you made contact with the live wire, your body would provide a link between the supply and the earth, so a current would flow through you.
Which two factors does the amount of energy an appliance transfers depend on?
How long the appliance is switched on for and the power of the appliance.
What equation links energy transferred, power and time?
E=P×t/ energy transferred=power×time
What is the name given to the maximum safe power an appliance can operate at?
The power rating
State the equation you can use to calculate the energy transferred from charge flow and potential difference.
E=Q×V/ energytransferred= chargeflow×potentialdifference
What equation links current, potential difference and power?
P=V×I/ power=potentialdifference×current
You know the resistance of an appliance and the current through it. What equation could you use to calculate the power of the appliance using these values?
P=I 2R/ power=(current)2×resistance
What is meant by ‘the national grid’?
The national grid is a system of cables and transformers that links power stations to consumers.
In the national grid, electricity is transmitted at a low current. Explain why this is an efficient way of transmitting electricity.
The lower the current in the national grid, the less energy is lost by heating in the cables.
In the national grid, what device increases the potential difference of the electricity supply?
A step‑up transformer
In the national grid, what is the purpose of a step‑down transformer?
To reduce the potential difference of electricity before it is supplied to consumers
