fizzics » Telecommunications

Finding the distance to a thunderstorm

mrmackenzie — Sun, 11 Jul 2010 12:50:49 +0000

The thunderstorm this morning reminded me that I was going to post something about calculating the distance to a storm.

Play this video and then replay it, paying close attention to the time index at the bottom. You will need to move your cursor over the video box to keep the time visible.

Lightning from Daniel Dingemanse on Vimeo.

Can you calculate the distance between the flash of lightning and the camera?

Hint: take the speed of sound in air as 340 m/s.

using frequency to remove vuvuzela noise

mrmackenzie — Wed, 30 Jun 2010 21:50:23 +0000

The Physics experts at Sixty Symbols have been playing with a vuvuzela. Here is a film showing their experiments on frequency and sound filtering.

www.youtube.com/watch?v=ATVbnilxIrs

total internal reflection

mrmackenzie — Tue, 30 Mar 2010 23:12:31 +0000

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.

inside a tv set

mrmackenzie — Sun, 28 Mar 2010 11:18:32 +0000

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?

S3 colour mixing

mrmackenzie — Tue, 23 Mar 2010 22:26:40 +0000

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.

S3 How a TV works

mrmackenzie — Sat, 20 Mar 2010 12:11:36 +0000

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

pixels
brightness control
moving the spot around the screen to produce an image
displaying many separate images per second

how a picture tube works

mrmackenzie — Tue, 16 Mar 2010 19:57:44 +0000

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.

Can you explain why there are two shadows of the Maltese cross on the screen?
What evidence can you remember from the lesson to justify your explanation?

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.

Why is the scanning pattern shown in this video different from the scan used in a tv set?

S3 Colour TV

mrmackenzie — Sun, 09 Sep 2007 22:25:19 +0000

We’ve been talking about colour tv in class and I found a few items you might want to look at. First of all, the website I used in class is available here and there is further information on combining colours here.

There is also a helpful animation of the shadow mask that stops the three electron beams from reaching the wrong phosphor dots.

S3 – How do you get a picture on a TV screen?

mrmackenzie — Tue, 04 Sep 2007 19:29:43 +0000

We’ve been looking at the demonstration picture tubes in class. Now we need to find out how to get from a single bright spot on the screen to having a picture covering the whole screen. Here is a link to the website I will be using in class to help explain how a picture is produced.

http://www.colorado.edu/physics/2000/tv/big_picture.html

S3 – shadow mask in a colour TV

mrmackenzie — Mon, 22 Jan 2007 21:04:34 +0000

An apology – I totally forgot that I had this animation on my laptop. It shows how the shadow mask prevents electrons from each gun hitting the wrong phosphor pixels on a colour tv screen.