Electricity Test Flashcards
What is a conductor?
a material that allows electrons to flow/ change positions
Ex. copper, aluminum
What is an insulator?
a solid, liquid or gas that resists or blocks the movements of electrons
Ex. rubber, wood
What is a voltmeter and what does it measure? How do you connect a voltmeter to a circuit?
a device used to measure potential difference/ voltage
it is connected in parallel (across the device being measured)
What is an ammeter and what does it measure? How do you connect an ammeter in a circuit?
a device used to measure electric current
it is connected in series
What is an ohmmeter and what does it measure?
a device used to measure resistance
Voltage
measures the difference in energy per charge between 2 points
the “force” that pushes electrons to go through a circuit
Unit: V
Symbol: V
Resistance
an opposition to the flow of charge
Unit: Ω
Symbol: R
Current
the flow of electrons
(the number of charges that pass by a particular point each second)
Unit: A
Symbol: I
What are the 4 factors that affect resistance?
- Material
- Temperature
- Length
- Thickness
Material
Silver has the least resistance but is very expensive to use in wires. Most conducting wires are made from copper
Temperature
as the temperature of the wire increases, its resistance increases and its conductivity decreases. A colder wire is less resistant than a warmer wire
Length
Longer wires offer more resistance than shorter wires. If the wire doubles in length, it doubles in resistance
Thickness
Wider wires offer less resistance than thinner wires. If the wire doubles in width, its resistance is half as great. Conducting wires that carry large currents need large diameters to lessen their resistance
Explain how cross-sectional area affects resistance:
the larger the cross-sectional area, the easier it is for electrons to flow. therefore, it will have lower resistance.
Series Circuit
a circuit that allows electrons to flow along only 1 path
Parallel Circuit
a circuit that allows electrons to flow along 2 or more paths
Describe Direct Current DC:
electrons move in a single direction
almost all battery powered devices are DC
Describe Alternating current AC:
charges are forced to reverse directions periodically
anything that plugs into the wall has AC current
What are the advantages of AC current?
It is easier and cheaper to transmit AC over long distances
Conventional Current Flow (I)
originally scientists thought electric current was the flow of positive charges (protons)
the resulting current is still called conventional current
Electron Flow (e-)
we now know that negative charges (electrons) flow
Ohm’s Law
If temperature remains constant, the resistance of the conductor remains constant and the current is directly proportional to the potential
V = I x R
What is the purpose of a circuit breaker?
It is a switch that protects a circuit against excess current due to an overload or short circuit. Unlike a fuse, a breaker can be reset
What is the purpose of a fuse?
A fuse protects the circuit by opening the circuit if the current gets too high. It melts and must be replaced
What causes an overload?
too many loads in parallel cause overloads
as new loads are added in parallel, there are more pathways –––> the total current increases
What is a short circuit?
a circuit with only a wire and source, where there is no load, the resistance is very low, so the current is very high and the conductors overheat
