Electricity Flashcards
What is potential difference
the measure of electrical work done by a cell or power supply. It can be called voltage.
What is an electrical current?
flow of electrical charge around a circuit
What direction do the electrons move in an electrical circuit and how is this shown on a circuit diagram?
they flow from the negative terminal to the positive but the diagram shows it the other way around.
What is the equation for the flow of charge?
charge flow = current x time Q = It Q = Coulombs I= amps t = secs
How can you increase or decrease the size of the current in a circuit?
- Change the size(pd) of the cell
- Change the number of resistors
- Use a variable resistor
What is the equation to show the relationship between potential difference, current and resistance?
V = IR V = pd volts I = current amps R = resistance (ohms)
What is an ohmic conductor?
It is when the resistor is directly proportional to the pd across it and is gives a straight line graph
What does the current- potential difference graph for a filament lamp look like and why?
The graph is a curve away from the current (y axis) so it is not proportional and is a non ohmic resistor.
What is a diode ?
It is a component of a circuit which allows the current to only flow in one direction.
What it a light emitting diode?
A component of a circuit which only allows current in one direction and lights up when a small current flows through it.
What is a thermistor?
It is a type of resistor which reacts to the temperature around it, increasing or decreasing it’s resistance.
It can be used to turn on or off other electrical circuits eg in a smoke or fire alarm and in a central heating thermostat.
What is an ammeter
It is a component which measures the flow of current and is set up in series with the resistor.
What is a voltmeter
it is a component which measure the potential difference across the resistor. It is always placed in parallel to the resistor.
What are the series circuit rules?
1 V supply = V1 + V2 +V3 etc
2 R total = R1 +R2 +R3 etc
What are the rules for parallel circuits
- the potential difference across each component in parallel is the same
- The total current through the circuit is the sum of the currents through the components
A total = A1 + A2 +A3 etc
What is a battery
It is 2 or more electrical cells
What happens to the potential difference of a battery when more cells are added in series?
The sum of the pd’s of each cell gives us the total potential difference of the battery- add them!
BUT the cells must be all facing the same direction otherwise they can cancel each other out.
What is the term for each of these letters
P, E, I, PD, Q, T, R
P = Power E =Energy I = Current PD = Potential difference Q = charge T = time R = resistance
What are the units that each of these are measured in? Power Energy Current Potential difference Charge Time Resistance
Power in Watts Energy in Joules Current in Amps PD in Volts Charge in Coulombs Time in seconds Resistance in Ohms
Useful equations
Q = I x t V = I x R P = V x I E = P x t E = V x Q
What is the difference between alternating current and direct current?
Alternating current changes direction. The number of times it changes direction every second is called its frequency and is measured in Hz
Direct current always travels in one direction.
What is the difference between direct and alternating potential difference.
Alternating PD changes direction and direct PD remains in the same direction
Describe the UK mains electricity
It has a pd of 230 volts and a frequency of 50Hz
What are the colours of the wires in a UK electric cable
Brown = live this carries the voltage to the appliance so 230V
Blue = neutral completes the circuit between the socket and the appliance carries 0V
Green and Yellow = earth carries 230V of the appliance is faulty otherwise it carries none.
What are the rules for series circuits?
- There is the same current through each componant
A1 = A2 = A3 - The potential difference of the power supply is shared between the componants
V supply = V1 + V2 - Total reistance is the sum of the resistance of each componant
R total = R1 +R2
What are the rules for parallel circuits?
- The total current (A) through the whole circuit is the sum of the current through each component
A1 = A2 + A3 - The potential difference across each component is the same
V1 = V2 = V3 - The total resistance of two resistors in parallel is less than the resistance of the smallest individual resistor
V1 < V2 therefore total resistance < V1
What is the potential difference of 3 cells of 1.5V joined in the same direction
1.5 +1.5 + 1.5 = 4.5V
3 cells of 1.5 V are joined together but one is joined the wrong way around what is the total potential difference?
1.5 + 1.5 -1.5 = 1.5V
What is a direct current?
DC is where the current always flows in one direction as in when the potential difference is provided by a cell or battery of cells
What is alternating current
AC occurs when the potential difference switches direction multiple times per second. The means that the current flows in different directions alternating from one direction to the other. This happens in mains electricity
What determines the amount of electrical energy transferred to an appliance?
- the power ( in Watts)
- the time it is on for (in seconds)
Explain how transformers increase efficiency in the National grid
- Higher voltage and lower current reduce the energy lost in heating up electrical cables used to transfer electrical energy through the network.
- A step up transformer increases the potential difference and decreases the current as it leaves the power station and goes to the pylons
- Step down transformers near homes decrease the potential difference and increase the current so that the potential difference is 230V going into houses, a much safer level.
