June 2011 G485-Fields, Particles and Frontiers of Physics

In a simple photographic flashgun a 0.20F capacitor is charged by a 9.0V battery. It is then discharged in a flash of duration 0.01s. Calculate the approximate resistance of the bulb.

How do you do that?

Answer in spoiler.

In a simple photographic flashgun a 0.20F capacitor is charged by a 9.0V battery. It is then discharged in a flash of duration 0.01s. Calculate the approximate resistance of the bulb.

How do you do that?

Answer in spoiler.

there's an equation for it isn't there? And that isn't ultrasounds its x-rays. isn't it?

ok what answer do you get for this for the total capacitance...show ur working.

Yes your right, but is that all we need 2 know, the equation??

please show how you got that answer

I get 0.05Ohm. :L Damn.

I reckon 2. 3+3 is 6 for the parallel bit. Then 1/3 + 1/6 = 1/6+2/6=3/6=1/2. So take the reciprocal to get C, which is 2/1, ie 2 microfarads or whatever the unit is.

I get 0.05Ohm. :L Damn.

I also got 0.05 Ohm as well. If someone else can confirm that 0.05 is the right answer it would mean my book is wrong. My book says 0.025. That's why I'm asking.

Well done lol

Making more sense everytime I read something about it.....i hate Ultrasound.

In the spec it just says about the thickness and the intial values.

I got 0.05 too but I think its wrong because...I found out initial Q from CV=Q and then found out current using Q=It and then used V=IR with V=9 but 9 is not the voltage across the resistor? is this how you did it?

I was thinking to use the exponential equation of Q=Q(initial)e^t/RC but we don't know Q?

I could be very wrong:

So far they have asked BIG| MARK questions on ultrasound and MRI. With that said, they also asked a mini question in jan on ultrasound. So its possible they could throw it in again- or not at all. I cannot find a paper from 2001 physics to g485, on PET, its new stuff, so they gotta test it at some point. They have done MRI and ultrasound already, so perhaps this time its PET's turn. They have asked about formation of a star and I believe olbers paradox in june 2010 - so it is possible that they could put a BIG MARKER in there on formaton of the universe.

In which I have put up a post already but here it is again:


A simple history of the universe, possible question:

Big bang
quarks and leptons existed freely ( at a temperature of around 10^14 K)
Quarks combined to form hadrons, such as protons (at a temperature of around 10^12 K)
atomic nuclei began to form by fusion ( at a temperature of 10^7K)
After 300,000 years atoms started to form as protons and helium nuclei grabbed electrons(temperature 10^4K). Note when the atoms formed there was more space for the radiation to move around in, so that the photons of radiation could pervade through space without being absorbed or deflected(this is what is meant by "the universe became transparent&quot.

Then matter began to clump together(gravity became the dominant force) and stars, galaxies, gas clouds and dust began to form. It mentions in the book the temperature range for this occurence(10^3 K to 2.7K) - and that the universe is saturated with electromagnetic radiation with a characteristic temperature of 2.7K
Then we have |TODAY|

I hope this was not too much, any questions, please ask.

Thank you!

That's how I did it too. I think my book might well be wrong !?

That's how I did it too. I think my book might well be wrong !?

Can anyone tell me about EMF produced by a AC. Generator.

Is this right?

EMF is Max when coil is parallel to the magnetic fields, EMF is 0 when it is perpendicular.