Electricity Flashcards
What is electric current?
The movement of charge through a closed, conducting circuit.
What is required for electric current to flow through a circuit?
- a source of energy
- a continuous pathway (no break in the circuit & a switch must be closed.
What is charge?
Electrical charge = electrons
What is the symbol for charge?
Q
What is the unit that charge is measured in?
Coulombs (C)
What is current strength?
It is the rate (how quickly or slowly) at which electrons flow through the circuit.
What is the symbol for current?
I
What is the unit that current is measured in?
Amperes (A)
Name the two sources of energy used in electric circuits:
- Cells (AKA electro-chemical cells)
- Generators (generate electricity)
What type of energy do cells store?
Chemical potential energy
What is the stored energy that a cell has called?
Potential difference or Voltage (V)
What happens to the chemical substances when a cell is connected to an external circuit?
They react and produce electrical charge with a high potential energy.
What is the energy transfer carried out by cells?
chemical potential energy → electrical potential energy
As the charge leaves the positive terminal of the cell and enters the wires, it has a high …. energy.
kinetic
What happens when the electrons reach a resistor?
They use/expend a lot of their energy and return to the negative terminal of the cell.
What needs to happen to the electrons when they return to the cell in order for them to re-enter the circuit?
They need to be recharged with high potential energy
What is a battery?
A battery is more than one cell connected together in SERIES. (meaning head to tail)
The more cells you put in series, the more/less chemical potential energy available for the charges (electrons) therefore the stronger/weaker the potential difference and current strength will be.
more
stronger
What is resistance?
Resistance is the opposition to the flow of charge
What is symbol for Resistance?
R
What unit is resistance measured in?
Ω ohms
What is a conductor?
Substances that allow charge to flow through them
What happens to the temperature of the conducting wire as the current passes through it?
It increases (heats up)
All conductors have a certain amount of … that opposes the flow of charge.
resistance
Give 3 examples of resistors:
Bulbs,rheostats & motors
Name all four factors that affect resistance:
- Type of material
- Thickness of the conductor (the wire)
- Length of the conductor
- Temperature of the conductor
How does the type of material affect the resistance?
Different conducting materials have different resistance to the current flow
List 3 different types of materials and what each one is used for?
- Copper -conductors
- Nichrome -heaters (weaker conductor therefore it heats up easily
3.Tungsten - light bulbs
How does the thickness of the conductor affect the resistance?
Thinner wires offer more resistance that thicker wires
(compare a wider passage with a narrow passage)
How does the length of the conductor affect the resistance?
Longer wires have more resistance than shorter wires
How does the temperature of the conductor affect the resistance?
Hotter conductors have higher resistance than colder conductors. Resistance is caused by collisions of the charges with the atoms.
Why do you think heaters have long coils of thin wire?
“The longer the length and the thinner the thickness of the wire the more resistance.” As a result, electrons passing through the long,thin wire expend/lose a lot of energy. This mean more energy is converted into heat and light in a heater.
What happens if the wires warm up?
The heat inthe wires is transferred to the electrons (as a result they gain kinetic energy)
∴ they collide more with the atoms that make up the conductor
MORE COLLISIONS = MORE RESISTANCE
What do we measure the total current that flows through a circuit with?
An ammeter
An ammeter is always connected in …. as the current needs to flow through it.
series
Why must an ammeter have a very low resistance?
So it doesn’t add to the resistance of the circuit.
What must the red connector connect to?
The positive pole of the battery
What must the black connector connect to?
The negative pole of the battery
What do you measure potential difference with?
A voltmeter
What is potential difference?
It is a measure of the difference in electrical potential energy between 2 points in a circuit.
What is the symbol for a voltmeter in a circuit?
V
What unit does a voltmeter measure in?
Volts (v)
Current does not flow through a voltmeter. Why?
They provide too much resistance
How must a voltmeter be connected in a circuit?
In parallel with the circuit
If a voltmeter is connected in parallel to a battery, what will it show?
It will show the total available energy of the battery (the potential difference between the positive and negative terminals.
If a voltmeter is connected in parallel to a resistor, what will it show?
It measures the potential difference between the two ends of the resistor
What is a series circuit?
A circuit with only one path for electric current to flow through.
What is the 1st important rule we have to remember when dealing with the series circuit?
If you increase the number of cells, connected in series ,then the current strength in the circuit and potential difference across the cells will increase as well.
What is the 2nd important rule we have to remember when dealing with the series circuit?
If you increase the resistance in a series circuit, by adding more resistors, then the total current strength decreases.
What is the 3rd important rule we have to remember when dealing with the series circuit?
The total potential difference across the battery is equal to he sum of the potential difference across each of the resistors. A resistor with a higher resistance will have a higher potential difference.
What is the 4th important rule we have to remember when dealing with the series circuit?
In a series circuit, current strength is the same at any point
What is the 1st important rule we have to remember when dealing with the parallel circuit?
When we connect two or more cells in parallel, the overall potential difference and the current strength is the same as if we only had one cell (the electrons only travel through one of the cells)
What is the 2nd important rule we have to remember when dealing with the parallel circuit?
As you increase more resistance in parallel, the total resistance of the circuit decreases and the current strength increases (there are more alternative pathways for the electrons.
What is the 3rd important rule we have to remember when dealing with the parallel circuit?
Potential difference across parallel pathways is the same
What is the 4th important rule we have to remember when dealing with the parallel circuit?
Current in each pathway adds up to the total current in the main branch
Q = It
Charge=CurentXTime
V = IR
Voltage=CurrentXResistance
1/Rp = 1/R1 + 1/R2
workingoutresistnaceinparallel
