ISTA – PGE & NQT Practical Sessions 1st Feb 2012

1. ISTA – PGE & NQT Practical Sessions1st Feb 2012 Some physics demonstrations

2. A block of iron in the flame Steel wool in the flame Metal expansion Weighing air ; atmospheric pressure Atmospheric pressure using syringe Blowing bubbles in deep water Blowing into a sealed bottle Magnet on pivot acts as a compass; force on pin (3rd law) Electromagnetism: magnetic effect of current; force between coil and magnet Electromagnetic induction: magnet in coil; two motors, windmill Simple speaker A simple spectroscope Fluorescent lamps produce discontinuous spectra Fraunhofer lines; star spectra Colour mixing Shadows Measuring height of trees Newton’s first law of motion Another plane Magnetic water Menu Rory Geoghegan. Science Education 2

3. Iron in the fire

4. A block of iron in the flame • When a large block of iron is held in the flame for 30 seconds the most noticeable change is that it gets... wet. • The water is one of the products of the combustion of hydrocarbons. • C4H10 + 6½O2 => 4CO2 + 5H2O(butane) Rory Geoghegan. Science Education 4

5. Steel wool in the flame • When fine steel wire is held in the flame it... burns, forming iron II oxide (FeO). Rory Geoghegan. Science Education 5

6. Metal expansion • A thin wire in tension balances the weight of a pivoted straw. • When the wire is heated with a small flame ( e.g. a match) it gets longer and the straw tilts downward straight away. • As the wire cools again it contracts and the straw returns to its original position. Rory Geoghegan. Science Education 6

7. Weighing air Air has weight (and mass); this accounts for atmospheric pressure

8. Weighing air • Find the weight of three litres of air using the apparatus shown. • Calculate the mass of one litre of air (at STP ?) Rory Geoghegan. Science Education 8

9. Sealed syringe as ‘pressure gauge’ • The 3 L bottle has a bicycle valve in the cap. • Inside there is a sealed syringe (e.g. 25 cm3) • The bottle is pumped until the air in the syringe is reduced to half its original volume. • Then the bottle contains twice as much air as it did at the start, but at twice the pressure. Rory Geoghegan. Science Education 9

10. Atmospheric pressure • Atmospheric pressure is due to the weight of air per unit area of the Earth’s surface. • If the atmosphere were uniformly dense it would be just 8 km deep (8000 m) • The mass of a cubic metre of air is ...1.2 kg • The weight of a cubic metre of air is ...12 N • The weight of air over each m2 of the Earth’s surface is ...12 N ×8000 1 m2 Rory Geoghegan. Science Education 10

11. 1 N/m2 = 1 pascal • Atmospheric pressure is about 100,000 N/m2 • i.e. 100,000 pascal (Pa) • 1 Pa = 1 N/m2 • 100,000 Pa might be written as 100 kPa • Meteorologists prefer 1000 hPa because the figures are about the same as they traditionally used — the millibar, now obsolete. Rory Geoghegan. Science Education 11

12. One ‘atmosphere’ (link) In metric units • pascal (Pa) = 101325.0270000 • millibar (mb) = 1013.2502700 • kilopascal (kPa) = 101.3250270 • bar (b) = 1.013250270 in imperial units • inch of mercury (in Hg) = 29.9213818 • centimetre of mercury (cm Hg) = 76.0002548 • millimetre of mercury (mm Hg) = 760.002548 in other units • pound per square foot (lb/ft2) = 2116.1711775 • pound per square inch (psi) = 14.6959793 • atmosphere (A) = 1.0000000 Rory Geoghegan. Science Education 12

13. Question • What force is required to pull the plunger of the sealed 20 cm3 syringe out to the 5 cm3 mark? • What force is required to pull the plunger out to the 10 cm3 mark? Rory Geoghegan. Science Education 13

14. Rory Geoghegan. Science Education 14

15. ... to the 5 cm3 mark • Approximately 32 newtons (32 N) Rory Geoghegan. Science Education 15

16. ... to the 10 cm3 mark • Again it is approximately 32 N • Why? In both cases we are pulling against the force exerted by the atmosphere on the plunger. Rory Geoghegan. Science Education 16

17. Can we estimate atmospheric pressure? • On what area is the force acting? • How can we find the internal area of cross-section of the syringe? • Here are two ways... 1. measure the internal diameter and calculate π r2 2. From the volume and the length calculate the area. (area = volume / length) Rory Geoghegan. Science Education 17

18. Finding the internal area of cross-section • The length to 20 cm3 mark is 6.3 cm so the area is 3.2 cm2. (20 / 6.3 = 3.17) • So the pressure is 32 N/3.2 cm2 = 10 N cm−2 = 100000 N m−2 Rory Geoghegan. Science Education 18

19. Blowing bubbles in a glass of water and in deeper water

20. Blowing bubbles in a glass - easy Rory Geoghegan. Science Education 20

21. Blowing bubbles in deep water (1 m) • At a depth of just 1 metre it is quite difficult to blow bubbles in water. • The pressure at a depth of 10 metres in fresh water is equivalent to one atmosphere. • At 10 metres the air in your lungs would be halved in volume and would therefore provide less buoyancy. Rory Geoghegan. Science Education 21

22. Could you blow into a closed bottle? • Could you blow bubbles into water in a closed bottle? • Let’s see. Rory Geoghegan. Science Education 22

23. What happened? • It is possible to blow bubbles in the closed bottle for a while. However the extra air increases the pressure inside the bottle and it becomes increasingly difficult to add more. • When you stop blowing the excess pressure forces some of the water out of the bottle. • Is this surprising? Rory Geoghegan. Science Education 23

24. Extension: bottle in free fall • Blow a little air into the closed bottle, but not enough to cause the water to be forced out. • Now let the bottle fall. • What happens? Rory Geoghegan. Science Education 24

25. Electromagnetism The force on a coil in a magnetic field

26. Small coil on a card • Wind a coil of about 30 turns of fine enamelled copper wire and stick it to a piece of light card using adhesive tape. • Remove the enamel from the ends of the coil and attach an audio lead. • Connect a battery and reversing switch. • Bring it near a compass or magnet on a pivot. Switch the current on and off. • Hold the card near a magnet and switch on the current. The card is attracted to or repelled by the magnet depending on the direction of the current. Rory Geoghegan. Science Education 26

27. Attach an audio source • Connect the coil to an audio source. • It makes no sound... ... unless it is held near a magnet. Rory Geoghegan. Science Education 27

28. Parts of a speaker • Magnetic field (usually a radial field across a gap) • Coil that fits into the gap. The audio signal is fed into the coil. • A diaphragm, usually of paper or other light material. This is attached to the coil. Rory Geoghegan. Science Education 28

29. A simple spectroscope

30. The outside and the inside • A ‘transmission’ version can be made by removing the metal layer of the CD-R. (works better with some makes). • The functional item in this spectrometer is a small piece (1 cm2) cut from a CD-R. Rory Geoghegan. Science Education 30

31. Alternative models • A reflecting version is easier to make and is probably more effective (lower image). Piece of a CD with metal film removed ca. 45° slit Piece of a CD, intact ca. 30° look in here Rory Geoghegan. Science Education 31

32. Spectrum of small fluorescent lamp Rory Geoghegan. Science Education 32

33. A simple spectroscope • Atomic spectra are not continuous – unlike the continuous spectrum of incandescent solids such as the filament of a bulb. Rory Geoghegan. Science Education 33

34. Fraunhofer ‘lines’ • By directing the spectroscope to a bright cloud or sky Fraunhofer ‘lines’ may be seen. • They are rather faint in this photograph. Rory Geoghegan. Science Education 34

35. Solar spectrum (sky or bright cloud) • Fraunhofer ‘lines’ can be discerned Rory Geoghegan. Science Education 35

36. Solar spectrum (sky or cloud) • Fraunhofer lines - somewhat clearer Rory Geoghegan. Science Education 36

37. Shadows

38. Sunlight in wood What do you notice? Circles? Why? Rory Geoghegan. Science Education 38 Rory Geoghegan. Science for the Primary School: Magnetism and Electricity 38

39. Shadows • Shadow of a card in different lighting conditions Rory Geoghegan. Science Education 39

40. Shadows • Shadow of a card in different lighting conditions Rory Geoghegan. Science Education 40

41. Can you predict the size of the image? Rory Geoghegan. Science Education 41

42. Can you predict the size of the image? Rory Geoghegan. Science Education 42

43. Rory Geoghegan. Science Education 43

44. The Sun 1 • Angular size in the sky: about 32’ = 0.53° • Tan (0.53°) = 0.00925 • 1 ÷ 0.0095 = 108 Alternative calculation: • Distance to the sun: 150 million km • Diameter of the sun: 1.39 million km • Ratio: 150 / 1.39 = 108 108 Rory Geoghegan. Science Education 44

45. Rory Geoghegan. Science Education 45

46. Rory Geoghegan. Science Education 46

47. Learning points The exercise can be used to teach, test or revise the following: • (Thinking, problem-solving) • Light travels in straight lines • Inverted images • Pinhole camera • Similar triangles • Similar proportions • Solving equations with fractions or proportions • Tangent of an angle Rory Geoghegan. Science Education 47

48. Newton’s first law of motion A ‘demonstration’

49. 5 m 20 m B52 over Vietnam Length 48.5 m Speed 230 m/s(ca. 515 mph) Rory Geoghegan. Science Education 49

50. Question • Why are the bombs directly under the plane? • The lowest one in the picture is over 20 metres below the plane and so was dropped 2 seconds before the picture was taken. Rory Geoghegan. Science Education 50