electric motors

`image by explainthatstuff`

We’re finishing off the electricity unit by looking at electric motors.  The page I used in class to help explain how a simple electric motor works is available here.

Here is another nice animation that shows the key parts of an electric motor.  It will stop after a few rotations but just reload the page to see it again.

Real electric motors have a few modifications;

• they use field coils instead of a bar magnet – the field coils form a strong electromagnet when current passes through them.  The field coils do not rotate.
• the single rotating coil is replaced by several rotating coils
• there are more contacts on the commutator – each pair connects to a different rotating coil
• the brushes are often made from carbon instead of metal – the carbon conducts electricity and can withstand high temperatures.  Carbon also moulds to the shape of the commutator to give a good electrical contact

`image by marrrci`

electrical wiring at home – the ring circuit

Wikipedia has a good description of how a ring circuit is used in home wiring.  The diagram below is neater than the one I drew on my board in class.  You can click on it to view a larger version of the drawing.

`drawing by Andrew C.`
• The ring circuit for power sockets is rated at 30A.
• The ring design allows electricity to reach the socket from two different directions, so the current flowing in any one wire is lower.
• Since the current is lower, a thinner cable can be used.  This saves money as copper is expensive.

S3 snow day work

I have uploaded a set of notes on the Using Electricity unit.  Please click on the download link below and save a copy on your computer at home.  I would like everyone to read up to the end of page 19.  This will cover everything that we have looked at so far on this topic.

Please try to answer as many of the questions in these notes as you can, either by printing out the pages and writing in the spaces or using your Physics jotter.

You may leave a comment if you get stuck with anything and I will try to help.

Snow day work for S3

If you can’t get to school due to the snow, here is some physics work so that you can keep up with the course.

We started looking at Ohm’s Law last week. Go to the HelpMyPhysics site and try the Ohm’s Law activities there.  I have also uploaded some additional problems taken from our classroom booklets. Click on the download link below to get your copy.  You can leave a comment here if you get stuck or want to ask a question.

S3 change to electricity test dates

Due to problems with school transport, I have moved the tests scheduled for today and tomorrow.  The general test will now be tomorrow (Tuesday 12th Jan) period 1, with the credit test on Thursday14th Jan (period 6).

The calendar on the right has been updated to show these changes.

S3 Electricity homework

Your homework for next week is attached.

Inside a Hoover

Here is the video we recorded yesterday.  I have trimmed the film down to 3 minutes in length so we can focus on the more essential aspects of the “hoover autopsy”.  You’ll notice that I have removed all of the conversations we had while the hoover was being filmed.

Your job is to tell me something about the things in the video.

It might be

• something about electricity you remembered from before the holidays
• maybe you learned something as we took the hoover apart?
• sharing information about something you can see in the video
• a calculation based on information you spotted in the video.

There are a few ways you can do this.

I uploaded the video to a site called Voicethread.  This site allows you to record voice or video clips as well as typing a comment.  It will also let you doodle on the video at any point if you need to highlight something.  Click on the Voicethread video where it says comment to share something you learned or remembered during the lesson or from the video.

The other way to make your contribution is to add a comment straight on to this blog.  You can do this by using the comment link next to this blog post.  Your comment will go into a queue for me to check it is not spam, so don’t expect it to go on to the blog straight away.

If you want to keep a copy of the video, feel free to click on the download link below.

Free physics software

I’ve had an email from Yenka to say that they are now offering many of their products for home use – free of charge!  I think Yenka is the new name for Crocodile Clips, the company who made Crocodile Physics and Crocodile Technology.  Their software allows you to create your own experiments to learn about

• motion – SG transport, Int2 unit1, Higher unit1, AH unit1
• electricity – SG using electricity, Int2 unit1, Higher unit2, AH unit2
• light and sound – SG health physics, Int2 unit3, Higher unit3, AH unit3
• electronics – Int1 applied practical electronics, SG electronics, Int2 unit2, Higher unit2

They also have some chemistry products you might find helpful.

The software is free but you can only use it at home.  Why not download it and see if you find it useful.

S3 – Alternative Summary Notes

I’ve uploaded a set of summary notes that you might find useful as you prepare for the end of unit tests on Using Electricity. Download the pdf file using the link below.

Summary Notes