Standard Grade

standard grade physics is in here

Communication satellite failed to reach geostationary orbit

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This video shows a European Space Agency Ariane rocket that was launched earlier this week.  The rocket was carrying two satellites intended for geostationary orbit, the W3B satellite for French company Eutelsat and a satellite for Japanese company B-SAT corporation, called BSAT-3b.

There’s lot of information in the clip.  The commentator tells viewers about the liquid rocket fuels (hydrogen and oxygen), the water dousing system used at liftoff and explains each stage of the rocket’s journey presentation.

The French W3B satellite was designed to provide TV, radio and internet services to Europe, Africa and the Middle East.  At 13:11 in the film, we can see the release of W3B.  Notice that the left side of the screen shows an altitude of only 1,200km at this point. This is not high enough to achieve geostationary orbit and the satellite must use its own propulsion system to reach an altitude of 36,oookm.

Unfortunately, W3B experienced propulsion problems and was unable to climb to 36,000km.  There is a BBC news report of the mission failure here.  The photograph in the BBC article is particularly good because, although the satellite is wrapped in protective film, we can clearly see two curved reflectors wrapped in silver film.

S3 telecommunications hw for 3.3 & 3.4

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Hello S3!

Here is your homework exercise on telecommunications.  I would like you to put the answers to each of these questions in your blue homework jotter and hand it in to me no later than Tuesday 14th September.  You will not receive credit for doing the homework if your jotter is handed in after this deadline.

Use the calendar on the right to check for any important dates (HW deadlines, assessments, parent evenings) during your Standard Grade course.  There is a podcast button under the calendar that will help you to subscribe to all future hw and answers on iTunes.  Just ask if you need help with that.

eBook Download (1211)

S3 how a TV works – part 3

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The site I have been using throughout the television section of the course is here.

The shadow mask makes sure that electrons fired from the filament responsible for each colour of sub-pixel do not hit the wrong phosphor dots, e.g. electrons sent by the “green” gun do not reach the phosphor dots that glow red or blue.  This animation shows how the shadow mask works.

S3 how a TV works – part 1

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Here is a short video clip showing how an image can be built up on a TV screen, one line at a time.  In a real TV set, the beam moves much more quickly (about 7000 m/s!) across the screen and 25 complete images are shown each second.

raster scan from mr mackenzie on Vimeo.

Remember that in a real TV set, the beam does not scan its way back up the screen but takes a “flyback” from the bottom right to the top left corner to start on the next image.

Podcast Video [ 0:12 ] Download (352)

Geiger-Müller tube

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We examined the operation of a Geiger-Müller counter today.

image by Theresa Knott

The Geiger-Müller (GM) counter is used to detect ionising radiation such as alpha and beta particles or gamma rays.  The radiation enters through a very thin window at one end of the tube.  This window is usually made of mica.

Mica flakes.  Photo by Rpervinking

Mica is a mineral that forms in layers called sheets.  These sheets can be split apart into very thin layers, so thin that even an alpha particle can pass through it (remember that alpha particles can be stopped by something as thin as your skin or a sheet of paper).  The mica window prevents the argon inside the tube from escaping and also stops air from getting into the tube.

When radiation enters the tube and collides with an argon atom, an electron may be knocked off the atom – we call this process ionisation.  When ionisation occurs, a positively-charged argon ion and a negatively-charged electron are produced.  The argon ion is attracted to the outside wall of the tube, which is connected to the negative terminal of the power supply, while the electron is attracted to the central electrode, which is kept at a high positive voltage – typically 500V.

A small pulse of current is produced each time an electron reaches the central electrode.  These pulses can be counted by an electronic circuit and a displayed on a 7-segment display.  Sometimes a small speaker is added to the system to produce a click for each pulse.  On its own, the GM tube cannot tell the difference between alpha, beta and gamma radiation.  We need to place different materials (e.g. paper, aluminium, lead) in front of the mica window to discover which type of radiation is responsible for the reading.

Here is a short video demonstrating the use of a Geiger-Müller tube.