with mr mackenzie
standard grade physics is in here
By coincidence (pardon the pun!), both Int2 and S3 have reached the stage of investigating total internal reflection at the same time. Here is a photo showing total internal reflection of a laser beam in a tank of water.
I’ve put together a short video showing total internal reflection in a semicircular block and a perspex model of an optical fibre.
total internal reflection from mr mackenzie on Vimeo.
We spent the last lesson of this term taking an old colour television apart. Even if you didn’t have the screwdriver, you were able to see the whole thing close up thanks to Ellie’s webcam and the digital projector. I have edited down the footage to around 2.5 minutes of TV destruction and added some still shots as well.
inside a tv set from mr mackenzie on Vimeo.
Can you use your knowledge of how a tv works to identify some of the parts as they are removed from the box? Leave a comment to tell me what you noticed. I’ll keep them secret until after the holidays so everyone gets a chance to reply. You can download a smaller version of the video from iTunes.
P.S. As we are now in the Easter holidays, I have left you an Easter egg. Who will be the first to find it?
We’ve moved from looking at forming a black & white image on a tv screen to creating a colour picture. I found a clever simulation that may help you to understand how coloured light is produced by mixing together different quantities of the three primary light colours. Click on the image below to go to the site. Use the red, green and blue sliders to adjust the colour that the man sees.
one less tv by Kevin Steele
Attribution-NonCommercial License
I showed you a handy site that explains nicely how all the parts of a TV set come together to produce a “moving image” on your screen. You can visit the site yourself by clicking here.
The site covers
Today we looked at the way in which a tv set produces a picture. We used the Maltese cross tube to produce the effect shown in this photograph.
Then we moved on to the Perrin tube. This allowed us to scan the electron beam across the painted end of the tube using the magnetic field of two Helmholtz coils. Here is the video clip we recorded at the time.
raster scan from mr mackenzie on Vimeo.
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.
Here is your HW exercise on the speed & acceleration work we have just covered in class. Please hand your HW jotter in no later than Friday 4th December.
Here are some revision notes for the unit test on electronics. Everyone (credit & general) has to know the white sections, the grey parts are the credit level topics.
Here is your HW for after the holidays. Please hand in your jotter by 30th October, thank.
On Friday, we examined the importance of Newton’s 3rd law of motion. In our discussions, different explanations for the motion of jets and rockets were proposed and considered. The front runners were;
Unfortunately, the lack of ground and air (or any other gas) meant that neither of these models were able to explain the propulsion of an object in space. It was at this point we remembered Newton’s 3rd law of motion (or here with non-rocket examples) from Standard Grade.
You’ve got to be careful with Newton’s 3rd law of motion, it’s easy to get confused. Bonus question: What’s wrong with this explanation?
I found a photograph that provides a stunning visualisation of Newton’s 3rd law in action during the launch of a DeltaIV rocket. You can read the details of setting up for this photo here.
image courtesy of Ben Cooper, Launchphotography.com
The photo was taken at very short range (about 30m) from the launch site and clearly shows hot gases being forced out of the exhaust at high speed. When a rocket forces out gas, the expelled gas pushes back on the exhaust with an equal force. Since the exhaust is part of the rocket’s structure, the entire rocket is propelled in the opposite direction to the gas.
It is this pushing back on the exhaust that provides thrust for a rocket. It doesn’t matter if the rocket is on the launch pad, in mid air or outer space. As long as it can push gas out of the exhaust, it will be able to propel itself forwards using Newton’s 3rd law of motion.
We don’t normally get a clear view of the hot gases being forced out of a rocket in launch photographs. A lot of the smoke seen in images like the one shown below is actually steam.
NASA/courtesy of nasaimages.org
There are two main sources of steam during launch. The most obvious is the burning of fuels but NASA also soaks launch platforms with water just before and after launch so that the massive sound waves don’t damage the vehicle being launched. There is a wikipedia article on the use of water during space shuttle launches.
