Current ElectricityIntroductory Physics

Canadian Academy

Group Members: Daiki Kieran Kebin

V

Current Electricity Construct and explain.

Work in pairs or by yourself for these tasks. With each question:

• Build it in the PhET simulation• Build it in the lab if possible• Draw the circuit diagram and

answer the questions on the slide.

http://phet.colorado.edu/en/simulation/circuit-construction-kit-dc

You should be able to:• Define current electricity• Define resistance and state the factors that

affect resistance in a metal wire• Define potential difference (voltage)• Explain the effect of potential difference

and resistance on a current• Draw basic circuit diagrams involving

batteries, lamps, switches and wires• Define electrical power including the

relationship to voltage and current

Your finished work should be uploaded to SlideShare (or

Google Docs if it works) and embedded into a blog post.

+ - + -

cell batterywire

junction

bulb/ lamp

cathode anode

switch

resistor

V A

voltmeter ammeter

Some basic circuit symbolsYou can use these to build the circuits on the next slides.

What do these two components measure?

electron flow

conventional current

A simple series circuitBuild this circuit.

Define current electricity. • Is the flow of electrons

Label the direction of flow of electrons and the direction of the conventional current. What is the difference between them?

Use the non-contact ammeter to measure the current in the circuit.

• It tells us the amount of amps.

What happens if the cell is not included in the circuit? Explain.

• There is no electrical current.

A

Switches and currentBuild this circuit.

Measure the current with the switch in the open position.

• 0 amps

Close the switch and measure the current. Explain your answer.

• 0.90 amps

Move the ammeter to different positions in the circuit and measure the current. Does position matter?

• Position doesn’t matter

Are electrons ‘used up’ in the circuit? Are electrons ‘created’ in the cell?

A

No, electrons are not used up.

No, electrons are not created.

Potential Difference (voltage)Modify the circuit to increase the potential difference by including two, then three, cells.

What happens to the bulb? • The bulb gets brighter

Measure the current and potential difference.

Complete the circuit diagram for three cells.

A

V

Define potential difference (voltage). • the difference of electrical potential between

two points.

Explain your results. • The more batteries resulted a brighter bulb. • V= 10A

Cells Current (A) Potential Difference (V)

1 0.90 9.00

2 1.80 18.00

3 2.70 27.00

Resistance (incandescent bulbs or lamps)Go to the following applet and see resistance at a molecular level and how a light bulb works.http://micro.magnet.fsu.edu/electromag/java/filamentresistance/

Explain in your own words how moving charges cause a bulb to glow. What energy transfers and transformations are taking place?

Explain what has happened when a cell (battery) has run out:The chemical within the battery runs out, not being able to move the electrons.

Resistance (incandescent bulbs or lamps)Build this circuit. Add bulbs and record your observations.

Bulbs Current (A) Observations

1 1.80 The bulb is very bright.The bulb has lost lots of

brightness, every bulb you add the less bright it

becomes

2 0.9

3 0.6

4 0.45

5 0.36

Explain your findings in detail. Everytime you add a bulb, it loses brightness, this is because the energy is shared. In detail, the more bulbs there are, the more atoms the electrons run into.

Remove all the bulbs to create a short circuit and measure the current. Explain. Everytime the distance of the distance of the wire increases, the amount of amps decreases, at the closest distance, there are 30,000 amps. Also the battery caught fire.

A

Conclusions Use your findings in the circuits so far to write your own Laws.

Law of current in a loop.“The current of electrons will always flow from the

negative side to the positive side, in order for electrons to flow everything must be connected.“

Law of voltage and current. (what’s the relationship?)

“ The more batteries, the more voltage. If there is more voltage, there is more current. The shorter distance,

the more voltage “ Law of resistance and current. (what’s the relationship?)

“ The more bulbs, the more resistance there will be “

Why is it dangerous to have too little resistance in a circuit?

Parallel Circuits How many different routes can current take through this circuit?

• Three routes

Close the lower switch only. Observe the bulb and measure the current.

• Only the top bulb is powered. The electron flows through the outer part of the circuit

Close the upper switch only. Observe the bulb and measure the current.

• Only the bottom bulb is powered. The electron flows through the bottom half of the circuit

Close both switches. Observe the bulbs and measure the current at different positions.• The bulbs are not powered. The current has stopped

Observe the animation carefully. What happens to the electrons at junctions? • The electrons split OR they are initially on top of each other, and they go towards different diresctions when they reach the junction.

Draw a circuit diagram for this set-up below:

Law of Parallel Circuits

Law of parallel circuits.“ The total current flow in the circuit is equal to the

sum of the current through all branches.“

Write your own Law, based on observations.

Now test your Law using a third bulb in parallel. Draw the circuit diagram below and write your observations of the bulbs and of current.

More Parallel CircuitsClose one switch at a time and record your observations.

• One bulb is 1.8 amps

Close both switches and record your observations. • The energy is shared with the middle bulbs

Carefully observe the junctions. What is happening? Explain with reference to resistance and junctions.

•

Do you need to modify your Law of Parallel Circuits?

Draw a circuit diagram for this set-up below:

More ResistanceUse two cells and two bulbs in a circuit. Use CTRL-click to adjust the resistance of the bulbs (one is 20 ohms (Ω), the other is 10Ω).

What is the difference between these two bulbs on a molecular level?•

Wire up the bulbs in two different circuits: series and parallel. Draw the circuits below. Under each circuit, record and explain your observations.

Series: Parallel:

Electrical PowerDefine electrical power and state its unit. •

What is the relationship between electrical power and ‘power’ as we have studied in the previous unit?

•

Compare two methods of generating electrical power: one fossil-fuel based and one renewable. How do they work? What are the benefits/ disadvantages of each?

ExtensionIf you finish with extra time:

• Check the Laws you have written against published information. Do they concur?• Find out more about circuits and their components. • Find out about the difference between AC and DC. • Build your own circuits and draw the circuit diagrams below.