Physics is what physicists do late at night.

Thursday, 5 March 2015

Congratulations
     to all scorers of distinction
          in Physics SPM 2014 !





Meh, meh, meh  the Goat be with you !

Tuesday, 28 October 2014

Sam Tet wish (SPM 2014)


Sam Tet wish 2014

SPM 2014 is around the corner.  
SMJK Sam Tet is a happy hunting ground for A, A, A, …… ,  .
May your blood, toil, tears, and sweat bear bountiful fruits.    

To all science students of Sam Tet in general, and to all students of 5S1, 5S2 & 5S7 in particular, may you all score A's in Physics.



And, to relay a message from the Physicists Hall of Fame:
"Befriend us, read our minds, understand our works, and we'll never fail you!"


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Wednesday, 22 October 2014

Calculating Wave Energy

Calculating the Energy Carried by a Wave

The diagram below shows the volume of a small slice of a medium carrying a wave
(longitudinal or transverse included).

What is the total amount of energy carried by a wave of speed v travelling through S, the
cross-sectional surface area in a certain time t?
 
The energy transported by a wave can be expressed by:
            E  =  2p2mf2A2    
where E is the energy of the wave, m the mass of a particle in the medium, f the frequency of the wave & A the amplitude of the wave motion.

The energy transported by a wave can also be expressed by:
            E  =  2p2rSvtf2A2    
where r is the density of the medium, S the cross-sectional surface area through which the
wave travels, v the speed of the wave, & t the time taken for the wave to travel the
   distance l.

Example 1:  A wave propagates from left to right with a speed of 3.0 ms-1 through a medium of density 1.4 kg m-3. Given that the frequency of the wave is 8.0 Hz. & the amplitude 60 cm. Determine the total wave energy that passes through a cross-sectional surface area of 5.0 m2 during a time interval of 40 s.   
Answer:   E  =  2p2rSvtf2A2 
                      =  2  x  3.142   x  1.4  x  5.0  x  3.0  x  40  x  8.02  x  0.62      
                      =  380,000 J  (2 significant figures)


Example 2:  The diagram below shows the graphical representation of 3 waves P, Q & R passing through the same medium during the same period of time.
(i)   Compare wave P & wave Q. Which one possesses more energy?
(ii)  Compare wave P & wave R. Which one possesses more energy?



Answer:  
(i)   Frequency of wave Q is 1.5 times that of wave P (3 Hz ¸ 2 Hz).
       There is factor of f2 in the wave energy equation.
       Therefore, wave Q possesses more energy than wave P by a factor of 1.52 or 2.25.   

(ii)  Amplitude of wave R is 2 times that of wave P.
       There is factor of A2 in the wave energy equation.
       Therefore, wave R possesses more energy than wave P by a factor of 22 or 4.   

Tuesday, 21 October 2014

Producing A Sound Wave

Using a Drum to Produce a Sound Wave

Prior knowledge: Longitudinal wave, compression & rarefaction.

See how a vibrating drum membrane produces a sound wave.
The longitudinal wave produced will propagate from left to right.

 
 
 
A sound wave can be represented by a sinusoidal graph as shown below.
 
 
 
 
 
 

Monday, 17 February 2014

STAR Mighty Minds trip to Dublin, Ireland (2014)

STAR Mighty Minds Winners 2013 Trip To Dublin, Ireland.
Date: 8 th - 15 th January 2014.