June 2011 G485-Fields, Particles and Frontiers of Physics

Original post by ChoYunEL

Can you do resistors? I like to look at Capacitors like resistors even though they're not :redface:

V=IR and Q=VC
In Series or a resistor is a parrallel for a capacitor :biggrin:

I understand the basics, it's just when they plonk two switches on, say one's open, one's closed, then both closed and then blahdeblahdeblah.
Having said that I just finished doing June 2010 and didn't do too bad in the end :smile:

Reply 182

M_I

In the specimen paper, question 8.d)i) why do the multiply by 100?

Reply 183

sulexk

OP

Why is the film in an intensifying screen sandwiched between two phosphor screens, what is the point of the second one, and what impact does this have on the resulting image produced?

Reply 184

InsaneFandom

3

Could someone please show me how you rearrange V=Voe^-t/CR to get t? :/

Reply 185

Oh my Ms. Coffey

Original post by InsaneFandom

Could someone please show me how you rearrange V=Voe^-t/CR to get t? :/

V/Vo = e^-t/CR

ln(v/vo) = -t/CR

ln(v/vo)x-CR = t

Reply 186

CoffeeStinks

Guys how does x ray diffraction provide evidence for the atomic radius being around 10^-10?

Please help. :frown:

Reply 187

Summerdays

10

Original post by Right Guard 3.D

The electrons travel through more volts so the eV (electron volts) increases.

An electron volt is a standard unit of energy meaning it can make eV= 1/2 mv^2 so increasing the voltake increases eV and increases KE :smile:

Yes. Loss of electrical potential energy (qV) = Gain of kinetic energy.

Reply 188

Original post by CoffeeStinks

Guys how does x ray diffraction provide evidence for the atomic radius being around 10^-10?

Please help. :frown:

Are you doing an old paper?
I'd probably start off with that equation from AS n(lambda)=dsin(theta)

Reply 189

sulexk

OP

I have been going through the june 2010 and jan 2011 paper, just looking over content, and so far for radioactivity, the smoke detector has not come up yet- so it is a possibility. In jan 2011 carbon dating had come up and in june 2010 half life came up. So perhaps the smoke detector will come up. Its a possibility. So here is how the smoke detector works:

The alpha particles are detected by an electronic circuit
When smoke enters the device the alpha particles are absorbed
and the current in the circuit reduces significantly and the circuit then triggers the alarm.

Note- alpha radiation is used because it is the most strongly ionising and therefore the most likely to be absorbed by the smoke particles. As well as this the range of alphar particles is so small that they're unlikely to constitute a hazard to the user.

Hope this helps. :smile:

Thank you

Reply 190

sulexk

OP

Original post by sulexk

Why is the film in an intensifying screen sandwiched between two phosphor screens, what is the point of the second one, and what impact does this have on the resulting image produced?

Any ideas?

Reply 191

Right Guard 3.D

13

Original post by Oh my Ms. Coffey

V/Vo = e^-t/CR

ln(v/vo) = -t/CR

ln(v/vo)x-CR = t

What does the x in the last line represent please? And I repped you since you firmed my understanding onhow to rearrange exponentials :biggrin:

Original post by Summerdays

Yes. Loss of electrical potential energy (qV) = Gain of kinetic energy.

Loss=gain? Doesn't that go against the law of conversation of energy? If energy is gained by an electron, wouldn't it also gain kinetic as the energies are 'like one'? Or am I getting confused?

Reply 192

Original post by sulexk

Any ideas?

I think the first phosphor screen absorbs X-ray photons and re-emits visible light photons. If I had to guess, I'd say the second one did more or less the same. The resulting image would be darker, because the film is more sensitive to visible light photons. So the image would appear crisper.

Reply 193

Summerdays

10

Original post by Right Guard 3.D

Loss=gain? Doesn't that go against the law of conversation of energy? If energy is gained by an electron, wouldn't it also gain kinetic as the energies are 'like one'? Or am I getting confused?

No, this IS the conservation of energy. Originally the electron had energy qV. As the electron is repelled from another electron, as it moves away from the otehr electron its potential energy (qV) is turned into kinetic energy. So energy is conerved. The electron gains maximum kinetic energy once the potential difference is zero (i.e.: once the electron is essentially an inifite distance away from the other electron.)

Reply 194

Right Guard 3.D

13

Original post by sulexk

Why is the film in an intensifying screen sandwiched between two phosphor screens, what is the point of the second one, and what impact does this have on the resulting image produced?

My book (Physics 2 for OCR A by Cambridge university press) doesn't show that it is sandwiched, it just has the phosphor screen and then the photocathode which elections are enjoyed from via the photoelectric effect. So id say there isn't really a point of the second one? Since the main focus are the elections emitted which then get accelerated to the anode?

Reply 195

CoffeeStinks

Original post by jam.wa

Are you doing an old paper?
I'd probably start off with that equation from AS n(lambda)=dsin(theta)

Yes it's Jan03. It doesn't directly relate to the new past papers but I'm trying to cover as many aspects. Just incase they want to go off on a tangent in the actual exam.

Thanks.

Reply 196

Right Guard 3.D

13

Original post by Summerdays

No, this IS the conservation of energy. Originally the electron had energy qV. As the electron is repelled from another electron, as it moves away from the otehr electron its potential energy (qV) is turned into kinetic energy. So energy is conerved. The electron gains maximum kinetic energy once the potential difference is zero (i.e.: once the electron is essentially an inifite distance away from the other electron.)

Now you said that, you were absolutely correct and I am annoyed for asking what I did :L

Thanks for clearing that up!

Reply 197

Oh my Ms. Coffey

Original post by Right Guard 3.D

What does the x in the last line represent please? And I repped you since you firmed my understanding onhow to rearrange exponentials :biggrin:

Loss=gain? Doesn't that go against the law of conversation of energy? If energy is gained by an electron, wouldn't it also gain kinetic as the energies are 'like one'? Or am I getting confused?

Multiply, I just kept it in there to show you multiply not divide.

Reply 198

Ralphus J

What does it mean by "describe the principles of ultrasound scanning"?? its on the specification sheet (OCR Physics A) under ultrasound (d). Please reply as soon as possible :smile:

Thanks

Reply 199