Electricity Flashcards
How does insulation work?
Flexible plastic around each wire prevents wires from touching each other or the user
How does double insulation work?
Appliances made of plastic / non-conductive material.
Devices with double insulation do not need an earth wire
What appliances should be earthed and how does it work?
Metal / conductor cased appliances must be earthed.
The earth wire is connected to the earth at 0V. It has very little resistance (less than the human body), so if the live wire worked loose and touched the metal casing, the extremely high current would take the path of least resistance to the earth, not the body. The extremely high current (due to very little resistance) triggers a fuse/circuit breaker.
How do fuses work?
A piece of wire that melts as a result of high heat caused by high current.
It is part of the live wire.
How do circuit breakers work?
Residual Current Circuit Breakers (RCCB) break the circuit if it detects a current that is too high.
It is fast and reusable but expensive.
How do resistors result in a transfer of energy?
How can they be used in a domestic context?
Resistors oppose current, generating heat.
The more current, the more heat generated - if two resistors are connected to a power supply the one with the less resistance will generate more heat as it allows a greater current.
Resistors can be used as heaters.
Relationship between power, current and voltage?
power = current x voltage P = IV
How do you select a fuse?
Fuses can be 3A, 5A or 13A.
Select the smallest fuse that is greater than the current generated by the appliance.
Relationship between energy transferred, current, voltage and time?
energy transferred = current x voltage x time
E = IVt
What is direct current (d.c.)?
Where is it used?
Direct current is where electrons are constantly flowing from one terminal to the other.
Voltage remains constant.
It is used in batteries.
What is alternating current (a.c.)?
Where is it used?
Alternating current is where the electrons alternate in which terminal they flow from/to.
The current changes directions.
It is used in mains electricity because electricity can be transferred from power stations to homes at a much higher voltage, losing less electricity.
In mains electricity alternating current happens at a frequency of 50Hz at 230V.
What are the key characteristics of a series circuit?
Where are they used?
In a series circuit voltage is split across the components (voltage at a particular component is a fraction of that at the power supply) while current is the same everywhere.
It is often used for Christmas tree lights.
What are the key characteristics of a parallel circuit?
Where are they used?
In a parallel circuit total voltage across each branch is the same as the power supply, but voltage is split between components within the branches. The current is split between branches according to resistance, the sum of the current through all the branches = the current through the source.
Used for domestic lighting because if one component breaks then the rest still function.
How does current in a series circuit depend on the applied voltage?
Current depends on voltage as current is directly proportional to voltage.
Current varies with voltage in wires, resistors, metal filament lamps and
diodes - how do you investigate this experimentally?
Place a power pack, the component and an ammeter in series.
Change the voltage using the power pack and record the effects on current on a graph.
