34.1-34.5: Flow of Charge, Electric Current, Voltage Sources, Electric Resistance, & Ohm's Law
Equation for Electric Current
*I=q/t* I is the current in Amperes(A) q is the charge in coulombs t is the time in seconds
Ohm's law equation:
*current=voltage/resistance* where current is in amperes voltage is in volts resistance is in ohms
Thus, 1 ampere=
1 volt/ohm
The resistance of a wire depends on...
1. the conductivity of the material in the wire 2. the thickness of the wire 3. the length of the wire 4. the temperature of the wire
Electric current is measured in...
Amperes (A)
Resistor
An electrical device that resists the flow of electrical current; helps protect sensitive electronics
_________ ________ are electrons in solid conductors that carry the charge through the circuit because they are free to move throughout the atomic network.
Conduction electrons. Positive charges cannot flow through solids because the protons are locked in place.
In a circuit, voltage, current and resistance can be related:
For a given voltage, as resistance increases, current decreases.
There is a difference between charge flowing through a circuit, and voltage being impressed ACROSS a circuit.
For example, water flows through a pipe, and there is a pressure difference between the ends of the pipe. The water flows through the pipe because of the pressure difference... the pressure does not flow through the pipe. Current and voltage are not the same thing!
This law can also be used with current as I, so it would look like..
I=V/R This still reads current= voltage/resistance
This relationship is called...
Ohm's law
Electric resistance is measured in...
Ohms (Ω)
Electric current
The continuous flow of electric charge through a material
Superconductivity
The resistance of some materials becomes zero at very low temperatures (approaching absolute zero)
Closed circuit
a complete circuit through which electricity flows
1 ampere is equal to...
a flow of 1 coulomb of charge per second.
Open circuit
an incomplete electrical circuit in which no current flows
When a group of electrons enters one end of a conductive wire, it pushes out..
another group of electrons on the other end. It does not have to make it all the way through the wire to create a 'flow'
The flow of charge will continue until...
both ends reach the same potential
When the ends of an electric conductor are at different electric potentials
charge flows from one end to the other
Good voltage sources, like batteries, balance potential differences between the terminals...
continuously over a long period of time.
Ohm's law states that the current in a circuit is...
directly proportional to the voltage impressed upon the circuit, and inversely proportional to the resistance of the circuit
The voltage provides the 'electric pressure' to move...
electrons between the terminals in a circuit
A battery with a conductive wire connecting both ends...
generates heat because there is nothing restricting the flow of electrons. This is where a resistor comes in handy.
In a fluid conductor, however, there may be positive and negative _______ as well as negative electrons that carry charge through the material...
ions
Thick wires have ____ resistance than thin wires
less
A resistor might be made of a nonconductive solid carbon mixture, or a...
long, thin coil of metal (long and thin are both properties that provide greater resistance)
Longer wires have ____ resistance than short wires
more
A greater temperature means _____ resistance
more (due to more jostling about of atoms)
Voltage sources such as batteries and generators supply energy that allows charges to...
move steadily.
Charge flows when there is a _________ __________between the ends of a conductor
potential difference
The technical chemical term for a reaction that involves the exchange of electrons is...
reduction-oxidation reaction, more commonly called a redox reaction (reduction is the gain of electrons, oxidization is the loss of electrons)
The amount of voltage that flows through a wire does not just depend on the voltage source...
the current also depends on the electric resistance
Electric resistance
the resistance that the conductor offers to the flow of charge
In electronics, for some reason, they still show current as flowing from the positive terminal to the negative terminal, or from higher potential to lower potential...
this wacky system is called 'conventional current' and remains the standard despite being proven untrue. The 'movement' of positive charge in a circuit is represented by the letter I.
Something that maintains or provide a potential difference for electric current to flow through a circuit is called a...
voltage source.
___________ is described as potential difference.
voltage. Voltage is also described as the potential energy per coulomb of charge that is available to the electrons moving between terminals, or as the electromotive force (emf)
A current carrying wire has a net electric charge of...
zero. The same amount of electrons enter and leave the wire, and this is equal to the number of protons at any point on the wire, so the net charge is zero.