Nov. 11 – Building Circuits

Learning Goals: Understand how to build circuits in series and in parallel.

Success Criteria: You can build working circuits in both series and parallel.

Today we got a chance to do some hands on work with electricity!  We used batteries, wires, bulbs and switches to build a variety of circuits.  Here is the handout:

Handout: Lab - Building Circuits

I hope everyone has an appreciation for the work that electricians do!  If you found it difficult to get one or two bulbs to light up, imagine doing the wiring for an entire house or building.

Homework: Study for the quiz.

REMINDER – The Unit Test for Electricity will be on Nov. 25th.

Doing well on the quiz is the first step to doing well on the test.

Good luck in your studies!

Nov. 8 – Review Power, Efficiency, Studying Strategies

To help you for the quiz here are some helpful studying tips:

Studying Tips

• Start early!
• Do a little bit each day.
• Give yourself a time limit and try to do the problems without looking at the solutions.
• Write your own test questions.

DO NOT wait until the last minute.

DO NOT look at the answers first.

DO NOT memorize the text book.

DO NOT memorize formulas (you will get a formula sheet!)

Quiz Topics

• Electric Current
• Electric Potential Difference
• Power
• Percent Efficiency
• Measuring Current and Potential Difference
• Cost of Electricity

Review

Here are some handouts to help you review for Power and Efficiency,

• Efficiency
• Electric Energy and Electric Power

There is one new item for today:

Power can be calculated if you know the current and electric potential difference.

To help you guys with reviewing and thinking about the quiz, I asked each of you to write your own questions that you think will be good for the quiz.  I will take one of the best ones and put it on the quiz!  So have a look at what your fellow students wrote.

Student Question:

A laptop computer uses a 80W adapter when it is plugged in.  Electricity costs 8 cents /kWh how much would it cost to use the laptop for 1 year for 6 hours a day.

More student questions:

• Student Questions Period 1
• Student Questions Period 4

Even more review!

• Current Electricity Practice Problems
• Power and Efficiency Practice Problems (with solutions!)

Homework

• Effectively study for the quiz.

Nov. 7 – Measuring Voltage and Current

Learning Goals:  Understand how to measure electric potential difference and current.

Success Criteria:  Draw circuit diagrams with voltmeters and ammeters.  Solve problems involving current and electric potential difference.

Handouts: 

• Current and Potential Difference Problems

Today I went over how ammeters and voltmeters are connected to circuits.  Have a look at these diagrams to see the difference.

Here is a typical circuit with three bulbs in series.

 Here are different ways to use an ammeter to measure current.

 Here are different ways to use a voltmeter to measure electric potential difference.

Here is what a real voltmeter looks like:

The red input is positive and the black input is for the negative end of the battery.

Then we watched some Mythbusters!

Video: http://www.youtube.com/watch?v=SU7xkYmWwmQ

This video is very informative because it shows that even experts can make mistakes.  The first half of their experiment had a lot of mistakes and they needed a professional electrician to help them out.  Also, they keep on using the terms "amperage" and "voltage" the correct terms to use are "current" and "electric potential difference".

Homework:

• Complete the handout.

Nov. 5 – Calculating Current and Potential Difference

Learning Goals: Understand what current and electric potential difference means.

Success Criteria: You can solve problems involving the calculation of current and potential difference.

To continue our discussion of current, I showed you guys what an ammeter actually looks like:

On the left is an old fashion one and on the right is a modern ammeter. (Actually the one on the right is called a multimeter that can measure much more than just current.)

Handouts:

• Current and Potential Difference Equations
• Current and Potential Difference Problems

The first handout has details of the equations we would use to calculate current and potential difference.

Watch this,

Video: http://www.youtube.com/watch?v=KprFTxjQAoE

Can you understand what is happening?  What are the big red spheres? (Protons!)  What are the little blue ones? (Electrons!)

Calculating Current

I = current, measured in units of Amperes (A)

Q = total charge, measured in units of Coulombs (C)

t = time, measured in seconds (s)

The equation is: 

And for those who prefer a triangle to look at:

Q is a measure of how much charge there is.  1 C is a lot of charge!  A single electron has this much charge:

It takes billions of billions of electrons to have 1 C!

Calculating Electric Potential Difference

E = energy, measured in units of Joules (J)

Q = total charge, measured in units of Coulombs (C)

∆V = electric potential difference, measured in units of Volts (V)

The equation is:

And for those who prefer a triangle, look at this:

Electric potential difference is also called "voltage" when speaking casually.  It is not an easy concept to understand!  

"Voltage" on it's own does not do anything, you need to have charges together with "voltage" to get any energy.  I give an analogy using a roller coaster.  For example, "voltage" is how high the hill is and charges are the people on the roller coaster.

A high hill by itself doesn't do anything.

You must have a cart and people on it before energy is released.

In the same way, electric potential difference (voltage) on its own doesn't do anything.  You must have charges involved before any energy is released, which leads to the equation, E = Q ∆V.

More charge will give more energy.  Higher potential difference will also release more energy, but they must both be present before energy is released.

Small charge and a lower potential difference will release less energy.

Small hill and small cart means less energy!

Homework: 

Complete the first handout: 

• Current and Potential Difference Equations

We will do the second handout together in class on Thursday.

Have fun going to work with your parents tomorrow!

Nov. 4 – Current

First I checked your homework from last week.  Here are the solutions to the first two questions.

• Power and Efficiency Problems - Solutions 

When I checked homework, many people did not do them.  I will not post full solutions until everyone has given them a try on their own.

Review of Circuits

We did a quick review of circuit diagrams:

I pointed out that not all circuits are strictly series or parallel.  The above example shows bulbs that are in series as well as parallel.

• Bulb A and C are in series.
• Bulb B and C are in series.
• Bulb A and B are in parallel.

Then we moved on to chapter 13.3

Current

Current is the amount of charge flowing per second.

Current is measured in units of Amperes (A).

How much is 1 A?

    1 A  is the same as 6.2e18 electrons per second!

The following table shows how your body would react to different amounts of current:

It turns out 1 A is a lot of current and will likely kill you if it goes through your body!

Based on the table, how much current is in a taser?

A taser delivers an electric shock that will cause a person to lose control of their body and collapse.
This will be in the 30 mA range.

Too much current can also damage electronic devices.  There are ways to control the amount of current in a circuit:

• A fuse is a wire that will break if the current gets too high.
• Resistors can be used to reduce current.

Current is measured using an ammeter.  The symbol for an ammeter is:

Ammeters must be connected in series.

Homework

• Practice more circuit diagrams. P 554 # 1-6

Nov. 1 – Presentations and Circuit Diagrams

Here are the final presentations that were given on Friday:

Period 1

• Hydroelectricity Powerpoint
• Nuclear Power Powerpoint
• Geothermal Prezi

Period 4

• Tidal Energy Powerpoint
• Nuclear Power Powerpoint
• Biomass Prezi

Then we started on Chapter 13:

Electric Circuits

Learning Goals: Understand the difference between series and parallel circuits.

Success Criteria: You can draw circuit diagrams for series and parallel circuits.

First of all you must understand these symbols and what they mean.

Here is an example of a circuit diagram:

As you can see the drawings are replaced with symbols.  You need to know how to draw these symbols!

There are two types of circuits you need to know about:

Series circuits have only one path for the electrons to move through.
The arrows show the direction these electrons move.

Parallel circuits have multiple paths for the electrons to move through.
They split into separate paths and then join together again.

Homework:

At this point, everyone should be working on the handout.

• Power and Efficiency Problems

If you are done the handout, have a try at these problems: P. 554 # 1-6.

Oct. 31 – Energy Presentations Continued

Here are more links to download other people's presentations:

Period 1

• Biomass Powerpoint
• Geothermal Powerpoint
• Solar Energy Prezi
• Hydroelectricity Powerpoint

Period 4

• Geothermal Powerpoint
• Tidal Energy Powerpoint
• Nuclear Energy Powerpoint
• Hydroelectricity Prezi
• Fossil Fuels Prezi

Last few presentations tomorrow then we move onto talk about electric circuits.

Homework:

Complete the previous handout,

• Power and Efficiency Problems