OCR Physics A G484: 20th June 2016

Reply 20

Super199

20

Can someone explain brownian motion to me and what the thing showed?

Reply 21

tobibo

2

Original post by Timon512

Place all of the apparatus in the thermally insulated container with a lid. Use an electronic mass balance to measure and record the mass of liquid in the beaker. Place thermometer into liquid to measure the initial temperature or you can use a temperature sensor and datalogger. Attach an Ammeter in series and a Voltmeter in parallel to an ELECTRICAL heater. Using an electronic stopwatch, measure the time taken for a given temperature rise. Change in temperature = Tf - Ti. As P=IV, W=IVT and as W=MC^T, C = W/M^T = IVT/M^T.

Just a quick follow up sorry, would you use a variable resistor to get different values for I and V (and also t with the stopwatch) to get multiple c values from which an average can be found? I've seen that in the past on revision websites but I'm not sure if we have to go into that much detail for this exam.

Reply 22

Timon512

1

Original post by tobibo

Just a quick follow up sorry, would you use a variable resistor to get different values for I and V (and also t with the stopwatch) to get multiple c values from which an average can be found? I've seen that in the past on revision websites but I'm not sure if we have to go into that much detail for this exam.

No there is no need for this. You are only using the I and V to work out how much thermal energy you have transferred. If you varied I and V you would get a tying amounts of the meal energy, varying changes of temoerature and varying values of C - so not in this case...

Reply 23

Samuel_Hodg

1

Anyone know how to get the June 2015 paper and markscheme?

Reply 24

ukcolBehT

2

For the paper: http://www.thestudentroom.co.uk/showthread.php?t=3670959&page=3

Question:
June 14 Q 3b ii) Why does the KE drop to 1/4 if height from which is dropped is halved?Wouldn't it also be halved?

Reply 25

Reda2

14

Can someone please help me understand moles further. I know that n = mass / molar mass, and number of particles = n * Na.
What else do I need to know. Thanks.

Reply 26

Samuel_Hodg

1

Original post by ukcolBehT

Question:
June 14 Q 3b ii) Why does the KE drop to 1/4 if height from which is dropped is halved?Wouldn't it also be halved?

Thanks for the paper.

I think they expected us to use the equation Vmax = (2pif)A
so if amplitude halves, max velocity halves and max KE decreases to 1/4.

(edited 7 years ago)

Reply 27

AlexeiLipov

5

Anyone understand Jan 2011, question 2(c)(i)? I understand the idea of a force due to mass being ejected, but why are we applying a decelerating force to move the satellite into a smaller orbit? In (ii), we work out the speed of the satellite increases when the orbit radius decreases, so surely you need an accelerating force to get a smaller orbit? Can anyone help?

Reply 28

Reda2

14

Original post by AlexeiLipov

Anyone understand Jan 2011, question 2(c)(i)? I understand the idea of a force due to mass being ejected, but why are we applying a decelerating force to move the satellite into a smaller orbit? In (ii), we work out the speed of the satellite increases when the orbit radius decreases, so surely you need an accelerating force to get a smaller orbit? Can anyone help?

According to F = GMm / r²
If GMm is constant, F is proportional to r², so if we want smaller orbit (basically smaller r) we need to increase the force, also because if you rearrange r² will be equal to GMm / F.

Reply 29

Reda2

14

Original post by Super199

Can someone explain brownian motion to me and what the thing showed?

It proves ideal gas assumptions.
Equipment: Light source, closed smoke cell, microscope.

If you look through microscope:
-You will see specks of light that are moving in continous random motion due to continues collisions with gas molecules.

Conclusions:
- Smoke paricles (what we see) are larger than gas particles (what we cant see)
-Random motion of smoke particles means gas particles are moving with random motion.
-Continous motion of smoke particles means gas particles has continous motion.

Hope this helps.

Reply 30

TheFarmerLad

22

Do we need G485 content for this exam?

Reply 31

EpicTree

10

Can someone help me with conversions from things like molar mass into mass, moles and all that because it's really confusing me

Reply 32

Tizzydag

3

Never seen anything on damping in past papers, maybe this is the year for it?

Reply 33

EpicTree

10

Original post by Tizzydag

Never seen anything on damping in past papers, maybe this is the year for it?

yeah there has been one or two things, like drawing on a graph what it looks like

There's not much they can ask really. The could ask about the experiment with the spring and card but thats it really

Reply 34

Reda2

14

Original post by EpicTree

Can someone help me with conversions from things like molar mass into mass, moles and all that because it's really confusing me

If you are given molar mass = 4.0 g mol^-1 then mass of 1 molecule will be

m = 4.0 x 10^-3 / Na

And number of moles = mass / molar mass
And # number of molecules = # moles * Na