TSR Physics Society

can i discuss some physicsy here?????????..........coz i think m not so gud at it............

Introductory quantum mechanics texts anyone? (online)

Yes, I have googled it, but haven't found anything really accessible. It's either too easy, too advanced or directed towards chemists (and no offence to chemists but it's much less mathematically rigorous and 'physically'-explained in some of the notes I've seen).

I can't believe that this is a solution to my boredom.

What kind of level are you looking for? This site has several undergraduate lecture courses including QM. I've found it pretty handy.

Hey physics is a great way of relieving boredom. I'm currently reading over some advanced EM notes I've found online

Thanks for the link!

Right, so I flicked through the upper level undergrad quantum mechanics course and I was fine... until it got to Fourier Transforms I don't cover that until second semester next year and I don't want to teach it to myself, as with maths I can easily confuse things if I teach it to myself and then receive formal teaching. Damn. Unless I can omit the stuff and carry on, but I dunno, I'd rather not risk it!

Any other links, perhaps?

Glad to know someone else is spending their free time with physics I think I'll take a look at the upper level undergrad electromag instead.

Hmm FT's are quite essential since they help in writing functions in terms of particular bases eg expanding wavefunctions in terms of energy eigenstates or converting between position and momentum representations but you dont need to know that much about FT, just the general form of it so it would probably be possible to read through and understand the majority of the notes without formal training in FT's.

There are several links that come up if you do a google search for quantum mechanics filetypedf.

EM is really interesting. Some of the advanced concepts are just amazing, I wish we'd been taught more than just the basics of EM theory

Right, I saw this on the BBC website, but I'm sure it's not correct.

Can anyone prove it?

Right, I saw this on the BBC website, but I'm sure it's not correct.



Can anyone prove it?

Question:

A 47micro Farad capacitor is charged to a p.d. of 15V and then discharged through 100K Ohm resistor. How long does it take for half of the energy stored in the capacitor to have the dissipated in the circuit?




[The answer is : 1.6 seconds if you wanna check]



Please help me!

Question:

A 47micro Farad capacitor is charged to a p.d. of 15V and then discharged through 100K Ohm resistor. How long does it take for half of the energy stored in the capacitor to have the dissipated in the circuit?




[The answer is : 1.6 seconds if you wanna check]



Please help me!

Hi! May I join? I'm applying for medicine, but I JUST LOVE PHYSICS!

Firstly since C=Q/V
Q=CV= 7.05x10^-4

Total energy, J= 0.5xQ^2/C=5.29x10^-3

half of total energy = 0.5J=2.64x10^-3
At this (half Energy), the Charge Q1=4.99x10^-4

Therefore Charge flown out of capacitor, Q2=Q-Q1=2.07x10^-4 (RMB THIS VALUE)

Avg voltage = (V+V1)/R=12.8V
Avg Current= AvgV/R=1.28x10^-4

Time taken=Q2/Avg Current= (2.07x10^-4)/(1.28x10^-4)=1.6s

NOTE: V1= voltage when capacitor at half energy. use 0.5CV^2=half energy to find!

+ rep me!!!! lol!

Couldnt you of just used:

$Q = Q_0e^{-\frac{t}{RC}}$

And the time will be when $Q =\frac{1}{2}Q_0$ Sooo:

$\frac{1}{2}Q_0 = Q_0e^{-\frac{t}{RC}}$

$\frac{1}{2} = e^{-\frac{t}{RC}}$

$ln0.5 = -\frac{t}{RC}$

$t = -RCln0.5$

Edit: Hang on I just realised it meant energy not charge lol

Where'd you learn all these cool stuff? Defo not in A-lvls?

YOU LIE!!!

yeah it is a-level, we actually just did it this week lol


Looking back if you look at the two equations:

$e = qv$ and $q = cv$

and then combine them to get:

$e = \frac{q^2}{c}$

and because "c" is constant then for the energy "e" to halve then "q" would have to decrease by a factor of $\frac{1}{\sqrt2}$:

$= (\frac{q}{\sqrt2})^2c$

$= \frac{q^2}{2c}$

$= \frac{1}{2}\frac{q^2}{c}$

$= \frac{1}{2}e$

so...

$\frac{q_0}{\sqrt2} = q_0e^{-\frac{t}{rc}}$

$\frac{1}{\sqrt2} = e^{-\frac{t}{rc}}$

$-rcln\frac{1}{\sqrt2} = t$

$t = 1.629s$

bam!