Wednesday, September 06, 2006 @ 4:54 AM
Preliminary Pure Physics
Practical Exam 5th September 2006
haha, i guess i didn't
really screw this one up. at least i know what was going on. 2 questions as
usual. first one's on the refraction of light with the optical pins and the
second's on the stability of wooden block. i was assigned to do the second one
first and after 45 min we'll do a switch with our partners.
i'm supposed to
measure and record of course, the height of the largest wooden block and measure
the angle which it is about to topple over. i had to do this with 2 other blocks
of different sizes. then, i'm supposed to tie the block together to get
different heights and repeat the experiment till i get 6 readings, after which
i'm supposed to plot a graph of the angle against the height. i got a curve, but
some of my friends drew best fit straight line graph.. that occurred to me, but
i stuck to my own instincts. from my graph, i'm supposed to determine the angle
at which a 125mm block will start to fall.i got 19 degrees. lastly, i had to
give one precaution. i had no idea what it was so i put down the method on
avoiding parallex error which i think is wrong because that's what i usually
put, and it's wrong. i got penalised 2 marks for not learning from my mistake
and correcting it. if i ever get that question right, i'll be really elated.
i'm lucky because i
discussed a similar practical that we did with my friends, while waiting for the
exam to commence, in the canteen. at 925am, we switched. i had time to read the
question before the switch, so immediately, i took the glass block to the
electronic balance at the front to measure the mass of the glass block. then i
proceeded to give the mean length, width and thickness of the glass block by
using a vernier calipers. ha, i do not know how to use that thing, but i guess i
got lucky because i got the correct readings. surprisingly, i even remembered to
check for zero-error before measuring. fortunately, the equipment was working
well. i had to calculate the volume of the block using the measurements i've
obtained and find the density by dividing the mass over volume. i also had to
state the dimensions of the surface which would give the greatest pressure when
the block is placed on a horizontal surface, but i did not bother to work out
the area because they said dimensions. i've to use what i've found out to
calculate the maximum pressure. luckily, i remembered to change the units to the
S.I. unit, but i'm not sure if it's right. i got 2000+ Pa anyway. next i've to
place 2 pins at an angle of incidence of 60 degrees, and then i've to pin
another 2 pins in line with them when viewed from the glass block. heh, i drew
the angle of emergence instead because i keep getting 40 to 50 degrees of
emergent angle (i'm supposed to get 60). well, so i got an angle of 26 degrees
for the angle of refraction. my refractive index of the glass is 1.97. i know
it's quite out because the refractive index of glass should be around 1.52 to
1.57. oh, i did not sketch the graph for the extension of the experiment.
actually i did, but i erased it off. 1 mark gone for not trusting my instincts.
okay, got to go, have
to study for tomorrow's physics mock exam. oh, i nearly forgotten this. thanks andy, again, for helping me to put back the 4 optical pins and the soft board.
