Download 2 Types Current

2 Types Current
• Alternating Current (AC)
• Direct Current (DC)
Circuit Diagram Components
• Wire:
• Resistor:
• Voltage Source:
Circuit Diagram Components
• Light Bulb:
• Open Switch:
• Closed Switch:
Warm Up 11
• A student compares the viscosities of two
solutions at room temperature. The student
uses a metal block and equal volumes of the
two solutions in identical containers. Which
procedure would provide the best comparison
of the viscosities of the solutions?
• A Determining whether the block raises or
lowers the density of either solution
• B Determining whether the block raises or
lowers the temperature of either solution
• C Measuring the volume of liquid the block
displaces in each solution
TAKS
• Bring a Sack Lunch
• Bring a good book or books
• Do NOT bring backpacks and purses
• Do NOT bring cell phones, iPods, etc.
Circuits
What is a Circuit?
• A path or paths that conducts a
charge
• A closed circuit occurs when:
– Charge can flow from start to finish
without interruption
– There are no breaks
• An open circuit has something that
stops the flow of electricity
Circuit Diagrams
• A simplified picture of a circuit
• Uses symbols to represent
components (pieces) of a circuit
• CORRECTION: symbol for a voltage
source
Schematic Diagram of a stereo amplifier
We won’t be getting this
complex.
Electric Circuits
• Usually composed of:
– A voltage source (battery, power supply,
plug)
– Wires or connections
– A load
Wires
Good wires have very low resistance
Why?
Hands On
• Using a multimeter, determine the
resistance of several different
components:
– Wire
– Battery
– Light bulb
– Resistor
– Diode
• Classify each item as a source, load,
Loads
• Anything that consumes electricity or
provides some resistance is a load
– Resistors
– Light bulb
– Electronic device
Potential Difference in a Circuit
• Potential Difference over the whole
circuit equals the voltage of the
source
Voltage drops across each load adds
up to the voltage of the battery.
Regardless of current or resistance.
10 V
30 V
5V
15 V
Short Circuits
• Occurs when a closed circuit does not
have a load (tiny resistance!)
Thinking Question
• Using Ohm’s Law, explain how this is
dangerous.
Short Circuits
• With little resistance and constant
voltage, current increases
• What does the current do?
– Usually transforms to heat.
3 Types of Circuits
• Series – Everything in on a single
path
• Parallel – Multiple paths
• Combination – Contains both Series
and Parallel circuits
Exit Ticket 3
• You have 3 light bulbs connected in
series. What happens to the other 2
light bulbs if the middle one breaks?
Warm Up 12 03.02.11
• Some students investigate the rusting rate of
four metals in saltwater. To best find the
rusting rates, the students should measure
the masses of the metals before the
investigation and at —
• A the same time and day during each week of
the investigation
• B different times and days during each week
of the investigation
• C any time during the first week of the
Step 1
• Copy the circuit diagram on the board
• Using the parts in the basket, build
the circuit
• Test the circuit by hooking up the
power supply
– Each light should be about equal
Step 2
• Unhook lights from the power leads
– Lights should be OFF
• Everyone needs to create the data
chart and fill it in.
• We will use the data as part of our
notes
Create a Data Chart
Light 1 Light 2 Light 3 Total
W of
each
light
V
across
light
V after
each
light
Create a Data Chart
Light 1 Light 2 Light 3 Total
I flowing
across
each
light
(calcula
ted)
Step 3
• Measure the resistance across each
light & record them in the chart
– Power needs to be off or you cannot
measure resistance!
– Measure from points C-D, E-F, G-H
– Use the lowest ohm setting of the
multimeter
Step 4
• Switch multimeter to the lowest DC
Volt setting
• Hook up your circuit to the power
source
• Measure the voltage across each light
& record
– Make sure your red probe is on the +
side and the black probe is on the – side.
– Measure from points C-D, E-F, G-H
Step 5
• Now, attach your black probe to the
negative power lead (I in the
diagram).
• We will measure the voltage drop
after each light
• Place red probe at B, record this
under “V after each light” “Total”
• For Lamp 1, measure at D. Lamp 2,
measure at F. Lamp 3 is H. Record
Step 6
• Now, calculate the current (I) for each
light by using Ohm’s Law (V = I*R)
• For the rest (except Current!) of the
“Total” column, add up the resistances
and voltages of each light.
• Calculate the current for I using the
Total Resistance and Voltage of the
circuit.
Warm Up 1
3.3.11
• The elements in which of these sets have
chemical properties that are the most
similar?
• A K, Ca, Sc
• B O, S, Se
• C Na, Ca, Y
• D P, S, Cl
Resistance and Series Circuits
• “Resistance Equivalent” of a series
circuit is the sum of all the resistances
• What is the Resistance Equivalent of
your series circuit?
Current and the Series Circuit
• Are the calculated currents roughly
the same?
• In a series circuit, current is
considered constant.
• Icircuit = Vcircuit / Rcircuit
Voltages and a Series Circuit
• Is there a pattern between the
individual voltages and the voltage
drop at each light?
• In a series circuit, the voltage across
a load is equal to the voltage drop of
the load.
Voltages and a Series Circuit
• Did the voltage drop equal the voltage
of the source?
• YES! It has to.
• Hook up 1 light in a series with the power
leads.
• Notice how bright the light is.
• Add a 2nd light. How is the light?
• Add the 3rd light. How is the light?
• Why did the light decrease in brightness?
• In series, the electricity has to pass
through each load. Current is slowed down
for the entire circuit.
Parallel Circuit
• Unhook all the lights.
• Hook up 1 light to the power leads using 2
wires. Notice the brightness.
• Hook up 2nd light to the power leads using
another 2 wires. Notice the brightness.
• Hook up 3rd light to the power leads using
another 2 wires. Brightness?
Parallel Circuit
• What happens to the brightness of each
light when you add another one?
• In a parallel circuit, current flows through
each path separately.
• Each load added, increases the current
drawn.
Measure Resistance in Parallel
• Unplug the lights from the power
• Create another data table exactly like the
one from yesterday.
• Measure the resistance of each light
– We need this for calculations
– It will be different from yesterday…even
though it shouldn’t.
Measure Voltage in Parallel
• Turn on the power for the lights
• Measure Voltage at each light
– Use 200 DC Volts setting
• Is the pattern different from yesterday?
Why?
• In a parallel circuit, voltage across each
path is the same because each path sees
Current in Parallel
• Calculate current using the measured
Resistance and Voltage
• Unlike a series circuit, current in a parallel
circuit is not constant.
• Light bulbs were equally bright,
meaning….?
• Each new path needs more current.