electricity Flashcards
What 2 things are needed for a charge to flow?
~The circuit must be closed (no open switches)
~Must have a source of potential difference
What is current?
The flow of electrical charge.
What does Q = It stand for?
Charge (in coulombs) = current (in amps) x time (in seconds).
Current through a component depends on…
~The resistance of the component
~The potential difference across the component
What does V = IR stand for?
Potential difference (in volts) = current (in amps) x resistance (in ohms).
What is the gradients for a resistor, filament lamp or diode graph?
1 / resistance.
How does resistance change with current?
~When current is increased electrons have more energy
~They collide with atoms in the resistor when they flow through it
~This transfers energy to the atoms causing them to vibrate more
~Making it more difficult for electrons to flow through the resistor
As resistance increases…
Current decreases.
How does resistance change with temperature in normal wires?
Same as with current as the atoms vibrate when hot.
How does resistance change with temperature in a thermistor?
Hotter temperatures mean the resistance is lower.
How does resistance change with length?
The greater the length the more resistance and the lower the current (electrons have to go through more resistor atoms).
How does resistance change with light in an LDR?
The greater the light intensity, the lower the resistance.
How does resistance change with voltage in diodes?
Diodes allow current to flow freely in one direction but in the opposite direction, it has a very high resistance so no current can flow.
In series circuits, current only flows…
In a single path.
In series circuits, current is the same…
Everywhere.
In a series circuit, potential difference…
Is shared across the whole circuit.
In a series circuit, the potential difference of the power supply =
The sum of the potential difference across each component.
In parallel circuits, current…
Splits into multiple paths.
In a parallel circuit, potential difference is the same…
Across each branch.
In a parallel circuit, the potential difference of the power supply =
The potential difference of each branch.
Why does the potential difference of the power supply = the potential difference of each branch in a parallel circuit?
Because the charge can only pass through any one branch.
In a parallel circuit, current is shared…
Between each branch.
In a parallel circuit, current through source =
Sum of current through each branch.
In a parallel circuit, total resistance is less than…
The branch with the smallest resistance.
What colour is the live wire?
Brown
What is the potential difference of the live wire?
230V.
What does the live wire carry?
Alternating potential difference from the supply.
What colour is the neutral wire?
Blue.
What is the potential difference of the neutral wire?
0V.
What does the neutral wire do?
Completes the circuit.
What colour is the earth/safety wire?
Green and yellow striped.
What is the potential difference of the earth/safety wire?
0V.
What is the function of the earth/safety wire?
To carry current, only if there is a fault.
What is the earth/safety wire connected to?
The earth and the casing.
What is power?
Energy transferred per second.
What 2 things is power directly proportional to?
Current and voltage.
What is the equation for energy transferred?
Energy transferred= power x time or energy transferred = charge x potential difference.
What energy is transferred in a motor?
Kinetic energy.
What energy is transferred in a kettle?
Thermal energy.
What is work done in appliances?
When charge flows through a circuit (and is equal to energy transferred) and all energy is transferred to the appliance.
What is the power rating of an appliance?
The power the appliance uses in watts.
The higher the power rating…
The more energy the appliance uses.
What is the national grid?
A system of cables and transformers linking power stations to consumers across the UK.
What do step-up transformers do?
Increase the potential difference from the power station to the national grid.
In step-up transformers, as power is constant…
Current decreases so less energy is lost.
What do step-down transformers do?
Decrease the potential difference from the national grid to consumers for their safety.
When 2 insulators are rubbed together…
~Electrons are transferred from one object to another
~This forms a positive charge on one object and a negative charge on the other
Why do sparks occur?
When a charge jumped through the air from a highly negative object to a highly positive object to try balance the charges.
