Topic 2.0: Controlling The Flow Of Electrical Current Flashcards
Conductors
Electrons are not tightly bound to the nuclei. They are freer to move.
Copper wire is a good electrical conductor. Other good conductors include: silver, Mercury and gold
Tap water is a conductor of electricity because of the many dissolved minerals it contains compared to the resistor of distilled water.
When no voltage is applied the electrons move around
When voltage is applied they all move in the same direction to the right
Superconductors
Have no resistance to the flow of electrons
They electrical conductivity decreases as the resistance to electron flow increases.
Insulators
Electrons are tightly bound to the nuclei.. They are not free to move.
Plastic or rubber are good insulators
Resistors
A type of conductor
Allows electric current to pass but provides resistance to do it. This limits the amount of current.
Distilled water acts as a resistor. The more charged particles that a solution had the better it conducts. Distilled water is not a good conductor because it contains only water molecules which have no electrical charge
Resistance
Is the measure of how difficult it is for electrons to flow through a substance
Measured in ohms.
The more resistance a substance has, the more the substance gains energy from each electron that passes through it
The energy gained by the substance is radiated to its surroundings as either heat or light energy.
Variable resistors or rheostats
Can gradually increase or decrease the amount of current in a circuit
Used to dim lights
Modelling voltage
Electricity can be compared to water:
Electricity comes from a source
Electricity encounters resistance
The more electrons the more powerful the current is in a conductor
Electrical generators
Keeps electrons flowing from the negatively charged terminal to the positively charged one
Modelling resistance and current
The amount of resistance in a circuit affects the electrical current
The current decreases as resistance is added
The shorter and thicker the wire, the less resistance it creates for electrons
Ohms law
States that as long as temp stays the same:
The resistance of a conductor stays constant and the current is directly proportional to the voltage applied
If voltage in a current increases, the current also increases
If a resistor of greater value is used but voltage stays the same, the current decreases
Voltage
Symbol: V
Unit: volts
Calculated by: current X resistance t
Measured with: voltmeter
Is potential difference between to points
A millivoltmeter is used to measure small voltages
Current
Symbol: I
Unit: amperes (A)
Calculated by: voltage divided by resistance
Measured with: ammeter
Small currents are measured using a device called a galvanometers
Resistance
Symbol: R Unit: ohms Calculated by: voltage divided by current Measured with: ohmmeter Lowest when a conductor is cool As temp increases resistance increases
Relationships between voltage, current and resistance
Voltage/ current: directly related because current is the measure of voltage that goes through a circuit
Current/ resistance: when there is more resistance it affects the current( bigger pipes have less resistance than smaller pipes)
Schematic or schematic design
Diagram using standardized symbols to show the components and connections in a circuit
Four basic parts:
A source- provides energy and electron supply
A conductor- provides path for current
A switching mechanism- controls current flow ( off & on)
A load- converts electricity to other forms of energy