Download Electric Current

Electric Current
Everything (water, heat, smells, …) flows from areas
of high concentration to areas of lower
concentration. Electricity is no different.
What makes electricity flow?
Potential Difference – the difference in voltage
between the ends of a conductor
- electricity will continue to flow until each end
has the same potential
Electric Current
Electric Current – the flow of electric charge
How is current measured?
Amperes – the unit used to measure electric
current
- it is a measurement of how much charge
passes a certain point per second
- 1 A (ampere) = 1 coulomb of charge per
second
If a wire is carrying a current through it
does it have a charge?
A current –carrying wire has a net electric
charge of zero.
- this is because the electrons that are flowing
through the wire to make the current are
leaving one end as fast as they are entering
the other end
Voltage Source
Voltage Source – an object that provides a
potential difference.
- examples are batteries and generators
Voltage Vs Current
-voltage is the difference in potential that
makes charges want to travel from one area to
another (like pressure) where current is the
charges that move through a conductor
Electrical Resistance
Electrical Resistance – how much a conductor
resists the flow of current.
- in wires resistance will change with the type
of wire and the thickness of the wire.
Superconductor – a material that has no
resistance to current at temperatures near 0K
Electrical Resistance
Ohms – the unit used to measure electrical
resistance
- the greater the resistance of a conductor the
more it will heat up when current is passed
through it.
- this is how a toaster works current is passed
through wires that have a high electrical
resistance so they heat up
Ohm’s Law
Ohm’s Law – the current in a circuit is directly
proportional to the voltage impressed across
the circuit, and is inversely proportional to the
resistance of the circuit.
-In other words, if I increase my voltage from a
battery it will increase the amount of energy
flow (current)in a circuit, the higher the
resistance in the circuit the less energy will
flow (current) in a circuit
Ohm’s Law
Current = voltage / resistance or I = V/R
Current is measured in ampere
Voltage is measured in volts
Resistance in measured in Ohm
What makes electricity dangerous
the voltage, current, or resistance?
The damaging effects of electric shock are the
result of current passing through the body.
DC Vs AC
Direct Current (DC) – a current that always flows
in one direction through a circuit
- this is the type of current you get when
you use a battery
Alternating Current (AC) – and electric current
that repeatedly reverses direction in a circuit
- AC it the type of current in your house
- it switches directions 60 times a second
or 60 Hz
Running a battery operated device
through AC
For a battery operated device to be used by
plugging it into a house electrical socket the
current that gets to the device must be in DC
Diode – a tiny electronic device that acts as a
one-way valve to change AC current into DC
current
The Speed of Electrons through a
Circuit
When electrons (electricity) is run through a
circuit the electrons themselves move vary
quickly but move through the circuit very
slowly
- this happens because there are so many
electrons around, they push each other away
so that each electron can not move through
the circuit quickly
When current is run through a
circuit, where to the electrons
come from that power electrical
devices?
- The electrons come from the conducting
material itself (not the battery)
- This happens because current moves through
a circuit very slowly. The electrons that make
it through the circuit are the ones from the
conductor (usually a wire)
Electric Circuits
You will need to be able to draw DC circuit
diagrams that include;
A switch
A voltage source (dry cell battery)
Resistors
Capacitors
Series Circuit
Series Circuit – a circuit in which devices are
arranged so that charge flows through each in
turn (one then the next, then the next,…)
In a series circuit to get the total resistance you
add all the individual resistances
R (total) = R1 + R2 + R3+ …
How to find the total resistance in
a series circuit
Since the current has to flow through each resistor
all you have to do to get the total resistance of a
series circuit is add up all the resistors
- What is the total resistance
of this circuit?
- What is the current running
through this circuit?
I = V/R = 25V/232Ω = 0.1087 ampere
Parallel Circuit
Parallel Circuit – a circuit where each electric
device is connected to the same two point of
the circuit so that each has its own path to the
battery.
To calculate the total resistance in a parallel
circuit,
R total = R1 x R2 / (R1 + R2)
How to find the total resistance in
a parallel circuit
Since all electrical devices in a parallel circuit have a
direct path to the battery they have to split the
current so if the resistors in parallel have the same
resistance the total resistance is half of that value.
-What is the total resistance
on this circuit?
- -What is the current running through this circuit if
the battery gave a voltage of 25V?
I = V/R= 25V/12Ω = 2.08 ampere
Pg. 710 – 711 in your book
Electric Power
Electric Power – the rate at which electrical energy
is converted into another form such as heat,
mechanical energy, or light
Electric Power = voltage x current or Power = V x I
Electric power is measured in watts
Current (I) is measured in amperes
Voltage (V) is measured in volts
Electric Power
If a 60 W light bulb is plugged into a 120 V
outlet, how much current does it draw?
Power = V x I
60 W = 120 V x I
Current = 0.5 amperes
Your Electric Bill
A kilowatt = 1000 watts of electric power
When you are billed for energy at your house
the energy company (Consumer’s Energy)
charges you per kilowatt hour used
Kilowatt Hour – the amount of energy
consumed in one hour at the rate of 1 kilowatt
If the energy company charges 10 cents per
kilowatt-hour, a 100W bulb can be used for 10
hours at the cost of 10 cents