# ISTA – PGE & NQT Practical Sessions 1st Feb 2012 Some physics demonstrations.

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ISTA – PGE & NQT Practical Sessions 1st Feb 2012 Some physics demonstrations

menu Rory Geoghegan. Science Education2 Menu 1.A block of iron in the flameA block of iron in the flame 2.Steel wool in the flameSteel wool in the flame 3.Metal expansionMetal expansion 4.Weighing air ; atmospheric pressureWeighing air ; atmospheric pressure 5.Atmospheric pressure using syringeAtmospheric pressure using syringe 6.Blowing bubbles in deep waterBlowing bubbles in deep water 7.Blowing into a sealed bottleBlowing into a sealed bottle 8.Magnet on pivot acts as a compass; force on pin (3rd law)Magnet on pivot acts as a compass; force on pin (3rd law) 9.Electromagnetism: magnetic effect of current; force between coil and magnetElectromagnetism: magnetic effect of current; force between coil and magnet 10.Electromagnetic induction: magnet in coil; two motors, windmill 11.Simple speakerSimple speaker 12.A simple spectroscopeA simple spectroscope 13.Fluorescent lamps produce discontinuous spectraFluorescent lamps produce discontinuous spectra 14.Fraunhofer lines; star spectraFraunhofer lines; star spectra 15.Colour mixing 16.ShadowsShadows 17.Measuring height of treesMeasuring height of trees 18.Newtons first law of motionNewtons first law of motion 19.Another planeAnother plane 20.Magnetic waterMagnetic water

Iron in the fire

menu Rory Geoghegan. Science Education4 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. C 4 H 10 + 6½O 2 => 4CO 2 + 5H 2 O (butane)

menu Rory Geoghegan. Science Education5 Steel wool in the flame When fine steel wire is held in the flame it... burns, forming iron II oxide (FeO).

menu Rory Geoghegan. Science Education6 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.

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

menu Rory Geoghegan. Science Education8 Weighing air Find the weight of three litres of air using the apparatus shown. Calculate the mass of one litre of air (at STP ?)

menu Rory Geoghegan. Science Education9 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 cm 3 ) 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.

menu Rory Geoghegan. Science Education10 Atmospheric pressure Atmospheric pressure is due to the weight of air per unit area of the Earths 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 m 2 of the Earths surface is...12 N ×8000 1 m 2

menu Rory Geoghegan. Science Education11 1 N/m 2 = 1 pascal Atmospheric pressure is about 100,000 N/m 2 i.e. 100,000 pascal (Pa) 1 Pa = 1 N/m 2 100,000 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.

menu Rory Geoghegan. Science Education12 One atmosphere (link)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/ft 2 ) = 2116.1711775 pound per square inch (psi) = 14.6959793 atmosphere (A) = 1.0000000

menu Rory Geoghegan. Science Education13 Question What force is required to pull the plunger of the sealed 20 cm 3 syringe out to the 5 cm 3 mark? What force is required to pull the plunger out to the 10 cm 3 mark?

menu Rory Geoghegan. Science Education15... to the 5 cm 3 mark Approximately 32 newtons (32 N)

menu Rory Geoghegan. Science Education16... to the 10 cm 3 mark Again it is approximately 32 N Why? In both cases we are pulling against the force exerted by the atmosphere on the plunger.

menu Rory Geoghegan. Science Education17 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 r 2 2. From the volume and the length calculate the area. (area = volume / length)

menu Rory Geoghegan. Science Education18 Finding the internal area of cross-section The length to 20 cm 3 mark is 6.3 cm so the area is 3.2 cm 2. (20 / 6.3 = 3.17) So the pressure is 32 N/3.2 cm 2 = 10 N cm 2 = 100000 N m 2

Blowing bubbles in a glass of water and in deeper water

menu Rory Geoghegan. Science Education20 Blowing bubbles in a glass - easy

menu Rory Geoghegan. Science Education21 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.

menu Rory Geoghegan. Science Education22 Could you blow into a closed bottle? Could you blow bubbles into water in a closed bottle? Lets see.

menu Rory Geoghegan. Science Education23 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?

menu Rory Geoghegan. Science Education24 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?

Electromagnetism The force on a coil in a magnetic field

menu Rory Geoghegan. Science Education26 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.

menu Rory Geoghegan. Science Education27 Attach an audio source Connect the coil to an audio source. It makes no sound...... unless it is held near a magnet.

menu Rory Geoghegan. Science Education28 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.

A simple spectroscope

menu Rory Geoghegan. Science Education30 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 cm 2 ) cut from a CD-R.

menu Rory Geoghegan. Science Education31 Alternative models A reflecting version is easier to make and is probably more effective (lower image). ca. 45° ca. 30° slit look in here Piece of a CD, intact Piece of a CD with metal film removed

menu Rory Geoghegan. Science Education32 Spectrum of small fluorescent lamp

menu Rory Geoghegan. Science Education33 A simple spectroscope Atomic spectra are not continuous – unlike the continuous spectrum of incandescent solids such as the filament of a bulb.

menu Rory Geoghegan. Science Education34 Fraunhofer lines By directing the spectroscope to a bright cloud or sky Fraunhofer lines may be seen. They are rather faint in this photograph.

menu Rory Geoghegan. Science Education35 Solar spectrum (sky or bright cloud) Fraunhofer lines can be discerned

menu Rory Geoghegan. Science Education36 Solar spectrum (sky or cloud) Fraunhofer lines - somewhat clearer

menu Rory Geoghegan. Science Education38 Rory Geoghegan. Science for the Primary School: Magnetism and Electricity38 Sunlight in wood What do you notice? Circles? Why?

menu Rory Geoghegan. Science Education41 Can you predict the size of the image?

menu Rory Geoghegan. Science Education42 Can you predict the size of the image?

menu Rory Geoghegan. Science Education44 The Sun 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 1

menu Rory Geoghegan. Science Education47 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

Newtons first law of motion A demonstration

menu Rory Geoghegan. Science Education49 B52 B52 over Vietnam Length 48.5 m Speed 230 m/s (ca. 515 mph) 5 m 20 m

menu Rory Geoghegan. Science Education50 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.

menu Rory Geoghegan. Science Education51 Newtons laws of motion In the 1st second each bomb falls 5 m. In that time the plane flies 230 m (almost five times the length of the plane). Each bomb moves with the plane at first (because it had that speed before it was dropped) and after some seconds the effect of air resistance is noticeable. It falls 20 m in 2 s, by which time the plane has flown almost half a kilometre. (alt. pic.)pic

menu Rory Geoghegan. Science Education52 Independence of components The vertical and horizontal components of the motion are independent. Neglecting some oscillation, the direction the bombs point is the direction of their velocity vectors – the sum of the horizontal and vertical velocity components. Their path is a parabola and their general direction points along the parabola.

menu Rory Geoghegan. Science Education53 Relative motion Tossing a coin looks no different in a plane or in a train than on the ground. If a coin has a horizontal velocity when it is tossed it retains it. To an external observer the coin would appear to move along a parabolic path. A local observer would simply see it going up and down.

Another plane Measuring distance and speed

menu Rory Geoghegan. Science Education55 Dublin Bay from Seapoint

menu Rory Geoghegan. Science Education56 How far away is the plane? At full zoom the FZ18 camera field width is 3.4°. Tan(3.4°) = 0.06. This is the ratio of the width of the field of view at the position of a given object and the distance to the object. The field is 16 times the length of the plane – an Airbus 300 (length: 54 m) with Monarch Airlines livery. So the distance is 16 × 54 ÷ 0.06 m, or about 14.4 km. 1 0.06

menu Rory Geoghegan. Science Education57 Google Earth The distance can be checked using Google Earth. The distance from Seapoint via the Ringsend chimneys to the line of the runway at Dublin Airport is 14.5 km Shadows of the tall chimneys at Ringsend power station Point from which the photograph was taken

menu Rory Geoghegan. Science Education58 The speed of the plane The pictures are taken at three frames per second. The plane travels about its own length (54 m) in 0.66 s Its speed is therefore 54 m ÷ 0.66 s = 82 m/s = 294 km/h = 183 mph MonarchMonarch Airlines, Airbus 300

Diamagnetism of water Water is repelled by a magnet

menu Rory Geoghegan. Science Education60 Concave water surface

menu Rory Geoghegan. Science Education61 Water is diamagnetic The picture shows a distorted reflection of a table lamp with a mesh in front of it. Water in the Petri dish just covers a neodymium magnet. The magnet repels the water; a concave depression is formed in the water surface.

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