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Making a Thermometer http://esfscience.wordpress.com/2012/01/23/making-a-thermometer/http://esfscience.wordpress.com/2012/01/23/making-a-thermometer/#comments Mon, 23 Jan 2012 10:13:12 +0000 http://esfscience.wordpress.com/?p=4579 ]]> 
The word ‘thermometer’ comes ultimately from the Greek thermos a
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metron, heat measurer. The bulb thermometer is the commonest. The thermometer contains a liquid, generally alcohol or mercury.
Bulb thermometers rely on the simple principle that a liquid changes its volume relative to its temperature. Liquids take up less space when they are cold and more space when they are warm (this principle works for gases and is the basis of the hot air balloon).
We tend not to notice that things like water, milk and cooking oil all take up more or less space as their temperatures change. In these cases, the change in volume is fairly small. All bulb thermometers use a fairly large bulb and a narrow tube to accentuate the change in volume. You can see this for yourself by making your own bulb thermometer from scratch. Here is what you’ll need – and thanks to howstuffworks
- A small glass jar or bottle with a water-tight lid - The lid should be the screw-on kind and made from metal or plastic. The jar needs to be glass so that its shape does not change when you squeeze it.
- A drill or a hammer and a large nail
- Some silly putty, plumbers putty, or even (chewed)chewing gum
- A drinking straw - quite long, the thinner the better, preferably clear
- Some food colouring (not required but makes it easier to see)
- Drill or punch a hole in the lid of your jar. The hole should be as close to the diameter of the straw as you can get.
- Fill your jar with cold water. You can do this either by filling it with water and leaving it in the refrigerator overnight, or by pouring ice water into your jar (straining the ice out in the process – all you want is water in the jar). Add food colouring if you want and shake it up. Put the jar on the table to keep it steady — you want the jar filled to the brim with cold water, as full as you can get it without overflowing.
- Put the lid on the jar as shown in the figure above. When you screw on the cap, a little water may spill out the sides, and a little water may be visible in the straw. That’s okay, don’t worry
- Place the jar in your kitchen sink, plug the sink and run hot water into the sink until the sink is about half full. Watch the level of the liquid in the straw and watch. As the water in the jar gets warmer, it will expand and rise up the straw. This sort of expansion happens every day, but we don’t really notice it because the amount of expansion is fairly small. Here, because we have routed the expanding water into a narrow straw, it is much more obvious. We can actually see it happening.
- Because the working fluid is water, it cannot measure temperatures below 00C(the water would freeze). It also cannot measure temperatures above 1000C (the water would boil).
- Because the “bulb” (the jar) is relatively large, it takes a long time for the thermometer to reach the same temperatures as the object it is measuring – perhaps as long a half an hour.
- It can’t follow rapidly changing temperatures, for the same reason.
- It’s big and awkward. We couldn’t use it t measure the temperature at a point.
- Because the top of the tube is open, the water can evaporate and pick up dust and debris.
How do you calibrate the thermometer? This means putting numbers on it and making a scale. To do this, we need two fixed points, temperatures which we know won’t change. The ice point is one – the temperature of pure melting ice. Immerse your bulb in pure melting ice and leave it long enough to settle down, Make a mark on the clear drinking straw – this is nought (0) degrees Celsius.
Now arrange to suspend your bulb over a pan of boiling water, just above the surface. The liquid will rise up the tube and when it stops ( to a fair approximation) it is measuring the temperature above pure boiling water at standard atmospheric pressure. This is our second fixed point which we can label 100 degrees Celsius. All we then have to do is make a linear scale on the straw from 0 to 100 and we have a way of measuring temperature.
The scale is linear.
- It’s not very sensitive – how could we make it more sensitive?
- It takes a long time to respond – how could we speed up the response time?
- It has a limited range – below 0 the water freezes, above 100 it boils. What could we do to extend the range?
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2011 – a good year http://esfscience.wordpress.com/2012/01/01/2011-a-good-year/http://esfscience.wordpress.com/2012/01/01/2011-a-good-year/#comments Sun, 01 Jan 2012 01:41:42 +0000 http://esfscience.wordpress.com/?p=4574 ]]>
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Qwiki http://esfscience.wordpress.com/2011/11/23/energy-for-year-9/http://esfscience.wordpress.com/2011/11/23/energy-for-year-9/#comments Wed, 23 Nov 2011 07:31:10 +0000 http://esfscience.wordpress.com/?p=4553 ]]> 
I typed the word ‘energy’ into the search box and this is what I got.
http://www.qwiki.com/q/Energy
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A2 Revision Papers http://esfscience.wordpress.com/2011/11/16/a2-revision-papers/http://esfscience.wordpress.com/2011/11/16/a2-revision-papers/#comments Wed, 16 Nov 2011 12:08:19 +0000 http://esfscience.wordpress.com/?p=4529 ]]>
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Moments and Parrots http://esfscience.wordpress.com/2011/11/02/moments-and-parrots/http://esfscience.wordpress.com/2011/11/02/moments-and-parrots/#comments Wed, 02 Nov 2011 09:35:56 +0000 http://esfscience.wordpress.com/?p=4537 ]]> 
It’s a hard life being a parrot. You have to stand up all day on your perch without falling off. Here’s a bigger Parrot document which is a picture of me. Cut me out without the branch I’m standing on and stick me on to a piece of thick cardboard which won’t bend. If you weight my tail, it will lower my centre of gravity so I can perch on your finger. Sweet.
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A2 Group. 40 marks for Eid http://esfscience.wordpress.com/2011/11/01/a2-40-marks-for-eid/http://esfscience.wordpress.com/2011/11/01/a2-40-marks-for-eid/#comments Tue, 01 Nov 2011 20:04:14 +0000 http://esfscience.wordpress.com/?p=4499 ]]> Image is from a real question, set in 2005A commendation is available for 80% or better.
A diagram is missing on the paper, about a magnetic field. Oops…
Here’s the missing diagram. L is the blue blob in the middle
A2 Mock Paper questions Nov 2011
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Electromagnetic Induction: Falling Magnets http://esfscience.wordpress.com/2011/10/19/electromagnetic-induction-falling-magnets/http://esfscience.wordpress.com/2011/10/19/electromagnetic-induction-falling-magnets/#comments Wed, 19 Oct 2011 04:25:41 +0000 http://esfscience.wordpress.com/?p=4496 ]]>
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Capacitors for IG http://esfscience.wordpress.com/2011/10/18/capacitors-for-ig/http://esfscience.wordpress.com/2011/10/18/capacitors-for-ig/#comments Tue, 18 Oct 2011 08:34:08 +0000 http://esfscience.wordpress.com/?p=4489 ]]> 
The simplest capacitor consists of two metal plates separated by an insulator or dielectric. We can pour + and – charges on to it by connecting the plates to opposite ends of a battery. We usually roll up the layers of insulator and conductor into a ‘swiss roll ‘ to save space. Just like milk bottles store milk, capacitors are components that are used to store electrical charge and are used with a resistor in timer circuits. When electrical power is supplied to a circuit that includes a capacitor – the capacitor charges up, in other words, a voltage develops across the plates. When power is turned off the capacitor discharges – its electrical charge leaks away slowly through a resistor.
This is useful in timers, also smoothing circuits where a current is changing and we want to smooth out the bumps. (see below)
slow charge up, slow discharge
Take a look at this link
When a switch opens the current tries to keep going by jumping across the gap creating a spark. (You can see this through the switch cover plate when you turn off a mains light switch).
This, of course, isn't the symbol for a capacitor
Adding a resistor – capacitor network across the switch absorbs the energy of the spark. This protects the contacts from being worn away.
Notice the circuit symbol for a capacitor
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Nobel Physics and the Fate of the Universe http://esfscience.wordpress.com/2011/10/04/nobel-physics-and-the-fate-of-the-universe/http://esfscience.wordpress.com/2011/10/04/nobel-physics-and-the-fate-of-the-universe/#comments Tue, 04 Oct 2011 16:09:22 +0000 http://esfscience.wordpress.com/?p=4467 ]]> 
Supernova explosion in the Large Magellanic CloudThe Nobel Prize for Physics 2011 was announced today. Three astrophysicists join a galaxy of numinous people, from Einstein to Heisenberg to Feynman for the big award in physics. They were looking at cosmic lighthouses, distant supernovae – the only objects bright enough to be observed at such vast distances – and they have concluded that the energy they emit is too faint, or, fainter than it ought to be.
So, the Universe isn’t just expanding, but its rate of expansion is increasing. The radius of the ball that is the Universe isn’t just getting bigger at a steady rate, the rate itself is increasing. So, energy from distant objects is being smeared out over a wider and wider area hence the light arriving on every square metre of Earth is less intense.
What does this mean? It means that the inflationary force of expansion of the early Universe plus other forces due to dark matter are bigger than the gravitational attractions wanting to pull all the bits together. It also means that Einstein’s fudge factor in 1917 to prevent the collapse of the Universe was probably right. It also implies that 70% or more of the Universe is dark matter energy which exerts repulsive (antigravity) forces. So, overall density is decreasing (?<1) and the dark and the cold will surely come…
But, not yet.
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Measuring the Acceleration of Free Fall with a Light Gate and Datalogger http://esfscience.wordpress.com/2011/09/28/measuring-free-fall-acceleration-with-a-datalogger/http://esfscience.wordpress.com/2011/09/28/measuring-free-fall-acceleration-with-a-datalogger/#comments Wed, 28 Sep 2011 07:59:41 +0000 http://esfscience.wordpress.com/?p=4444 ]]> The logger is programmed with the length of each interrupt card ( I used 40mm), weighted a little bit to minimise air resistance and dropped vertically between the light gates.
we needn't worry about dropping it from the same height each time, since a=constant
The internal clock starts when the gate is interrupted and stops when it is not. It then calculates the average speed of each part of the double card as it falls. One speed is greater than the other because the card is accelerating. The internal clock in the logger records the time between the interrupt cards’ fall. Acceleration = change in speed / time.
The logger software can be used to display all speeds and times, or the calculated acceleration directly, which is simpler. Results were as shown.
As you see, all readings (should all be 9.8) are in error by approximately the same amount. This indicates a systematic error in the readings, perhaps because the weight of the card is unevenly distributed or the card lengths are not quite precise enough.
These eight determinations can be output to a spreadsheet and their average calculated
This is the calculation:
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