There were no lectures today, just tons of hands-on experiment so it means, much more fun!
(Pictures/Videos from Yan Yu denoted by *) --------------------------------------------------
5. Equipotential Curves of an electric field.
We had to arrange the setup as shown below. The centre piece was positively-charged and the two blocks at the sides were negatively charged.
Using the probe connected to a voltmeter, we had to search for points 4V, 8V and 10V. Once found, a strong pressure is exerted on the carbon paper to note the positions. From the positions of the points, we can draw the equipotential lines.
Using a barometer and a thermometer setup, we can measure how volume of a gas varies with temperature. This is based on the equation pV=nRT.
The water is heated to 90 degrees Celsius and used to heat a gas to the same temperature. The gas expands pushing the mercury down. To keep the pressure at a constant 1 atm, the tube on the right containing another gas of 1atm is slided up or down so the mercury level remains the same for both tubes.
The volume occupied by the gas is calculated by measuring the length of tube it requires using the volume formula of a cylinder. At regular temperature intervals, we note the volume. Plotting a graph, we realise what was taught in theory all this while. A gas becomes less ideal as the temperature drops.
This experiment is about elastic and inelastic collisions. Something that many JC students only know in theory all these while.
The air track contains many tiny holes. An air pump blows air through these holes so the glider and slide on the surface without much friction.
The light/photogates as introduced by Physics SPA just 3 days ago!*
It consists of a laser beam fired from one side to another. These photogates is different from the SPA as just one gate is enough to obtain the velocity. This is due to the bar code printed on glider. The two gates here are for measuring the velocity of the two gliders.
4 Gliders on air-track. The ones with the rubber bands demonstrate elastic collisions while the pin and hole (2 extreme right) perform completely inelastic collision.
2 moving gliders collide elastically.*
Elastic collision of a moving glider with stationery glider.*
Elastic collision of moving glider with stationery glider with repelling magnets.*
We investigated the parabolic path of a water of a particular velocity.
Using the circular markers attached to the strips, we plotted the points at different parts of the path. We repeated this a few times with different water velocities and initial angles of the water jet. This experiment really wasted a lot of water in the name of science!
This is the only one without any pictures. The videos say everything!
A piece of powdery material Yttrium Barium Copper Oxide (YBa2Cu3O7 or YBCO) is wrapped in aluminum foil to form a tablet-sized shape. The tablet is then immersed in liquid nitrogen for about a minute. Yes, LIQUID NITROGEN! The temperature is about -190 Celsius.
At this temperature, YBCO loses its electrical resistance becoming a super conductor and floats on a magnetic track!
YBCO levitated on magnets
YBCO levitated on magnets (2) *
YBCO levitated under magnets
The concept is about the opposing forces of gravitational and forces induced by the magnetic track. The track is made up of numerous bar magnets placed horizontally. Thus the magnetic field lines produced are parallel to the ground.
As the gravitational forces pull the YBCO down, the movement cuts the magnetic field lines causes induced currents (Faradays' laws) to flow within YBCO, this causes an induced force which pushes the thing back up. Thats why the YBCO appears to be jiggling as it moves round the track.
A superconductor has to be used so as to ensure that the current flowing within it does not dissipate as heat. Scientists are currently experimenting to find a material that can act as a superconductor under room conditions. The uses of this breakthrough are endless, more efficient power transimission, cheaper maglev trains and more powerful computer chips etc.
This is the first time I saw such a superconductor in action in real life! I only saw it being demonstrated in the same manner in documentaries.
A powerful 40mW green laser is shown into a sample containing numerous microscopic glass beads. One of the glass beads is attracted and held onto by the laser. This phenomenon is utilised to manipulate objects at this scale since physical options are pretty much unavailable.
The laser light undergoes total internal reflection when it hits one of the internal walls of the bead. This reflection changes the momentum of the photons. Since total momentum is conserved, the a force acts on the wall of the glass. When the bead moves, the larger momentum change when a more intense beam at the centre of the ray pushes the bead, keeps it stationery.
It is here that I found out that my green laser has a power range between 8mW and 14mW as the student manning this station had a handheld tester. Much more than the Class 3A <5mW printed on it. In this range, my laser should be a Class 3B. Think it is still within the local legal limits for civilian lasers. My red laser only has a puny 45 uW.
This photo spectrometer machine measures the absorption of certain wavelengths when a monochromatic light passes through a transparent/translucent material.
Got two sensors. One sensor measures the amount of output the other acts as a control.
The results of a blue filter
Range of x-axis changed to reflect visible spectrum.
(Click to view) This measures the level of absorptions of multi-coated spectacles from Yan Yu and I. Mine (red line) seems more absorbent then hers (blue line). However, her blocking cutoff range is larger than mine so its more effective. My specs blocks out alot in the visible range which is useless!!!
Four participants had to volunteer from each school. That had to Yu Xuan, Yan Yu, Yingyu and me. ( So many Ys, lol). Those 0725 ppl left... 4 of the remaining NYJCians participated in the audience round.
The questions that were asked were mostly general knowledge questions in Physics. But four of us were like stumped one question after the next. Calculation questions also give so little time. Sian diao! The last was a test of the reflexes. Aiyah, got negative points for that too! Not really fair lah, this quiz depended too much on luck too.
Surprised by the winners? The hot favourites RJC, and HCI combined team did not even make it in.
The cert as usual, collected too many to count in my JC life. The pin was a souvenir for every participant. That rectangular bottle was also a souvenir from the UV spectroscopy experiment. Used to house liquids to be tested. The end? Yes, I better end...
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