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

• D Measuring the time it takes the block to sink 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, or wire.

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

5 V 15 V

10 V

Voltage drops across each load adds up to the voltage of the battery. Regardless of current or resistance.

30 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 investigation• D one randomly selected time during the investigation

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 brightness

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

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 (calculated)

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 the data

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 the same starting and ending voltage.

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.