A level and fluorescent tube

[ericmark]

A level wiring

• ericmark
• 12 Mar 2011
• 1

This is the diagram out of an A level Physics book. I am sure many would agree if a student followed this diagram the tube would be damaged burning out heaters and if it did start it would draw well over the design current.
It states:-

The tube has a `filament' electrode at each end. The starter unit
is necessary because the mains voltage is too small to ionise the vapour in the tube when the electrodes are cold. When the tube is first switched on, the gas (argon) in the starter 'switch' unit conducts and heats the bimetallic strip, making it bend, so the switch closes. The current through the starter unit increases enough to heat the filament electrodes. When the bimetallic switch closes, the gas in the starter unit stops conducting, and so the bimetallic strip cools and the switch opens. The mains voltage now acts between the two electrodes, which are now hot enough for ionisation of the gas to occur.

There is nothing about the back EMF or the current limiting qualities of the ballast.
It continues with statements like:-

Did you know that the UK government is stopping the sale of filament light bulbs? We will need to use low energy light bulbs instead.

This is just after it has explained how the fluorescent tube contains two filaments.
This is "A" level one wonders what ordinary level students are now taught? OK maybe the student does not need to know all the information but I shudder to think what would be the result if a budding student was to try to follow the instructions given. And if the tube was around the 20W mark or less it may even fire up hope they have included a fuse?

 

[JohnD]

have you written to the publishers yet?

 

[DeadJoe]

35 years ago, they were teaching the physics of fluorescent tubes at 'O' level. I remember because I was there. How times change.

 

[ericmark]

From same book this question:-

(b) A light source is observed through two pieces of Polaroid, which are initially aligned parallel to each other. Describe and explain what you would expect to observe when one of the Polaroid’s is rotated through 360°.

Polaroid is the trade name of a optics manufacture famous for cameras which developed the film inside the camera.
Polarising filters are made with 4 main types
* Linear
* Clockwise circular
* Anti-clockwise circular
* So called circular which is a linear filter and quarter wave filter combined.
The latter is now the most popular as the plain linear stops the electronics of a camera working and if these lenses are used it would depend which way around they are turned.
If the quarter wave filter which is camera side is between the two filters then turning the filter will only effect the view of the light source if the source is giving out polarised light.
If the non camera sides are placed together then rotating them will reduce the light it for 90°and then increase it for 90° assuming starting at maximum light position.

There is no book answer only calculation answers are given but since it does not explain the different types of filter in the text I suspect the authors were referring to old linear filters.

One minute they are talking about

An atom in an excited state can de-excite directly or indirectly to the ground state, regardless of how the excitation took place. Therefore, an atom can absorb photons of certain energies and then emit photons of the same or lesser energies. For example, a mercury atom in the ground state could:
• be excited to its 5.7 eV energy level by absorbing a photon of energy 5.7 e V the mercury could then
• de-excite to its 4.9 eV energy level by emitting a photon of energy 0.8 e V then
• de-excite to the ground state by emitting a photon of energy 4.9 eV Figure 4 represents these changes on an energy level diagram.

The next it is very simplistic and also uses such poor English as to mean it has to be read a few times to work out what they really mean.

Yet in the exam they are so pedantic as to remove marks because a student names the units in the table rather then in the headers. I wonder how many mature students ever get good marks as one would not normally worry about conventions.

We all know we should write 10 kW and not 10kW and there should be a space between figure and unit but does that really matter? Surely they should be teaching Physics not worrying about how it is written out?

 

[bernardgreen]

Is it any wonder that students coming out of higher education are confused when they try to use the in-accurate knowledge that has been taught to them.

I recall my daughters were taught several errors in both O level and A level courses. Most worrying was when some of the "knowledge" taught at O level was contra-dicted by the "knowledge" taught at A level. When challenged the staff claimed that the "knowledge" at 0 level was tailored to be easier to understand and A level students were more able to understand the reality. They couldn't understand why the A level 1999 was so different from the A level 1964.

 

[JohnD]

Describe and explain what you would expect to observe when one of the Polaroid’s is rotated through 360°.

The author doesn't understand use of the apostrophe, either.

 

[Adam_151]

An interesting read in the link below, I know its references the books used by the US education system and quite a few decades back at that, but it illustrates that this isn't unique or modern day issue only...

http://www.textbookleague.org/103feyn.htm

(p.s. if you ever see the books of the annecodes told by fenyman in a bookstore, I'd recommend buying them )

 

[bobdabuilda]

Describe and explain what you would expect to observe when one of the Polaroid’s is rotated through 360°.

The author doesn't understand use of the apostrophe, either.

There is much debate on the orthography of that!

 

[JohnD]

Greengrocer's

 

[Stoday]

If the quarter wave filter which is camera side is between the two filters then turning the filter will only effect the view of the light source if the source is giving out polarised light.

Illiterate solecism — she should have written "affect".