WELCOME TO PROTONS FOR BREAKFAST AUTUMN 2009 WEEK 4: GLOBAL WARMING 1 PfB11 Week 4 These are the feedback questions & comments from Week 3 along with my responses. For everyone’s sake, I have removed any mention of people’s names. Understood & Not Understood Michael says… I understand better the Excellent. Heat is the total energy of the microscopic difference between heat and jigglings and Temperature is a measure of the average temperature. speed of those jigglings. I don’t understand how the various Which bits? bits of kit work! Understood: Absolute Exactly correct about temperature! zero = no motion, so The fundamental interaction between particles is electrical. If two there is no “below” stationary particles – let’s say two electrons - interact then there absolute zero. Hence its interaction is purely electrical and described by the same rules as name! governed our experiments with balloons and sausages. If either electron is moving then the interact is still described as electrical. Did not understand: The However, if both electrons are moving, then in addition to the difference between an electric force, we describe their interaction as having an additional electric field and the component that we call magnetic. Clearly this can’t be fundamental magnetic field. In fact, because, as first elucidated by Einstein, if one travelled at the right are they different or speed, then one of the electrons would be stationary relative to us the same, or similar…? and the interaction would then be described as purely electrical again. So Einstein discovered that magnetic fields are just ‘what an electric field looks like’ when we observe moving charged particles. Does that help? 2 Understood & Not Understood Michael says… Reversible and non-reversible magnets All magnetic materials lose their magnetic order at high I’m sure when I was at school we temperatures – as we saw with Terbium and Iron. You were told that some materials, once are talking about how a material behaves in an applied magnetic could not be reversed (you magnetic field. The reversible or non reversible showed us reversible magnetism in the behaviour is too complex to explain here, but it is not iron paperclip…). Maybe it was steel fundamental. Iron atoms are always magnetic, but some they talked about? Don’t remember. types of steel are easily magnetised (i.e. are attracted to the magnet) and others are not. The difference in Glare of lights I noticed last week behaviour arises from the way magnetism of the atoms on the way home the glare of street is able to change in an applied field. This is controlled lights and car lights !" is this like by the number of crystalline defects put into the a diffraction pattern? Is this caused magnet. by the glass plate or the air particles, or both? Glare can be diffraction, but also arise from scattering. One thing I understand: That the Scattering is when particles (which can be atoms or weight of molecules affects the small droplets) absorb light and re-radiate it in all energy it has to vibrate ∴ affects the directions. energy it emits. One thing I didn’t understand: So IR Yes. The heavier the object, the slower it vibrates and visible are the radiations we give under a given force. And if it vibrates more slowly it off and use all the time ….. how about emits a lower frequency electromagnetic wave. the others … is it a case of these are the only range of wavelengths/ All the ranges of the electromagnetic spectrum are frequencies our molecules can make ‘used’ naturally – and we have developed technological use of. tricks to use some ranges. Obviously radio waves and microwaves (Week 5) are very helpful. Infra red and visible light are used for a huge number of activities. Ultra violet light is used too, as are X-rays and Gamma rays. I think we have found ways to measure and exploit almost all of the electromagnetic spectrum! I really enjoyed the dry Excellent. ice! I am glad you enjoy them – they take ages! Great slide shows. I remember the pumpkin-weighing well : what a lovely day that was. *Remember I was at the pumpkin allotment 2nd It depends on what is known as the heat transfer coefficient place. *The camera man! between the object and my hand. The heat transfer coefficient I understand magnets and between my hand and the liquid nitrogen is exceptionally low (for a nitrogen. short time) because of the Leidenfrost effect. Similarly the heat I don’t understand how you transfer coefficient between my hand and the balloon is low have to wear gloves for because of the poor heat transport in the balloon. So when my nitrogen but sometimes fingers touch the rubber of the balloon, I warm up a thin layer of you don’t. rubber and that stays insulated even from very cold rubber nearby. But if I touched a metal object which has been cooled by liquid nitrogen, then I would need gloves. 3 Understood & Not Understood Michael says… I understood that there are atoms Excellent! everywhere. I also understood what happens Mmmm. Not sure I understand what you mean – to the atoms when they heat up and cool down. how ‘it works’? I didn’t understand how the liquid nitrogen works. I am glad you found it interesting and happy It was very interesting!! that you liked the ice cream. (Lowed the ice-cream – great idea)! I understand that there are atoms everywhere. Excellent! I didn’t understand how liquid nitrogen works. Did you speak to the person above? Very enjoyable and informative evening. I am glad you found it enjoyable Really good – surprise, surprise! I am glad you enjoyed it and the Another interesting and fun discussion. ice cream. The ice-cream was ACE! “A must-have at parties!” Absolutely! 1. Atoms move faster 1. Yes, atoms do move faster when heated, but I am not sure that is when heated. This must the reason for body movement. However the chemical reactions which be a reason for the need activate our muscles are slowed down when we are cold, and so it is for body movement. A certainly true that we need a certain level of atomic motion in order static posture would be to move. unhelpful. 2. Tricky. Light is certainly absorbed and emitted in quanta – small 2. Does light move in packages as you put it. No one know exactly how it moves except that quanta – i.e. discrete it must be wavelike otherwise there could not be interference as we packages? saw in Week 2. 1. Temperature Absolutely! related to The centre of the Earth is very hot because the outer pat of the Earth is a atoms jiggling. very good thermal insulator. The current high temperature of the centre of 2. Why is the Earth arises from the original high temperature of the Earth. Once the centre of earth crust had formed, the hot inner Earth was no longer exposed directly to the very hot? cool space around it. On average, only 0.1 Watts of power reaches each square metre of the Earth’s surface from below. This compares with (on average) 240 Watts per square metre input from the Sun. Also, the decay of naturally occurring radioactive elements has heated the Earth. The expanding and contracting balloon It is indeed fascinating is fascinating. If we’re made up of We don’t expand and dilate in that way because the atoms etc why do we not dilate when atoms in our bodies are in a mixture somewhere we’re cold and inflate when we’re hot. between the solid and liquid state. We do expand a I like the way you use the word little bit when we get hot, but not very much. balance now and again because I think Yes, there are a great many processes around us which that God made such perfect balance. appear to be in balance, which makes one think… Jiggle, jiggle, jiggle, no wonder we are Indeed. Everything seems to be busy, busy, busy at the such frantic creatures. moment. 4 Understood & Not Understood Michael says… By demonstrating the heating of the Excellent. It’s the jiggling of the atoms that destroys paper clip I could understand how it the ‘ordered’ state of the magnetism. lost its magnetism. Look in the notes or download the PowerPoint slides: I wish I could remember all that was they may help you remember. demonstrated! Don’t worry we will do that again this week. And I couldn’t get to grips the information possibly the next week. about the molecular model and what they are/do. Heat is atoms jiggling around – the Exactly. more they jiggle the higher the temperature. We use to liquid nitrogen cool things for all kinds of What is liquid nitrogen used for? reasons. When we came up with an idea do the When we think, we metabolise glucose, and yes, our atoms in our brain jiggle faster and brains will heat up. therefore give off more heat? I love it that the world It is indeed wonderful. is made up of atoms or stuff as you call it. How Yes. The amount of damage done depends on how cool your body gets, wonderful. not on how cold the cold object is. Dry ice is solid carbon dioxide. Would dry ice or liquid When one touches dry ice, the atoms in ones hands are slowed down ice give freezer burn or dramatically very quickly – this can damage the cells resulting a cold damage your body more burn.