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.
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.
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.
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
pixels
brightness control
moving the spot around the screen to produce an image
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.
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.
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.
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.
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