It's going to be very jam packed! Awesome, you've done really well getting into those :) I was so disappointed about Space Camp... By the time I found out about it the applications had closed :( I had to find out about these all myself as my school isn't very good about showing the possible opportunities available.

Attachment 217149Attachment 217150

okay so i can do all of the question apart from 4. b) i. does the vertical component of the initial velocity (the speed the cable car is travelling at) need to be taken into account?

someone please give me a hint

I have no idea what is going on in the system you just described. I'll try to work it out and get back to you! Thanks though! :)

I agree, it asks for two things, which could be non-linear, and a positive correlation. My other thought would be you could say: angle of incidence > angle of refraction (which would mean the light is going into a material of higher refractive index than it came from), otherwise can't say much about the graph.

Apologies for mentioning snells law, but it's always interesting to push yourself a bit, and you already knew it really knowing about taking the sine of the angles.

Hope that's useful

So the question is asking you to draw the movement of point P against time as the wave passes through. It's checking to see if you understand what an amplitude vs time graph represents for a wave passing a given point.

Start by drawing points which can be easily calculated and then interpolate (join them up):

The wave is traveling at 0.5 m/s and as the intervals given are in convenient 0.25 m steps, the wave will take (0.25/0.5) seconds (t = distance/speed) starting from point X to reach point P.
So the first point will be 0 amplitude at time t = 0.5 seconds. i.e. the time it takes X to get to P. Plot this point on the graph.

Now pick the next zero. i.e. the next point when the wave crosses the x-axis. How long does it take to reach P from it's starting position? Plot that on the graph.

Do these same steps for all the zero crossing points.

Now start with the maximum and then minimum amplitude points: How long will each one take to reach point P from their starting positions? What does the energy in the wave do to point P? i.e. in which direction will point P move and what amplitude will it reach as the wave passes through? Plot these points.

This gives you enough points and the insight to now sketch the resulting curve. Be careful to include all of the line from 0 to 2.5s as the question states.



How did you get on?

I know the difference but excitation is a part of the photoelectric effect right? The electrons have to be excited in order to the emission of electrons to occur. Am I right? :)

Yes but it's the total energy of the system that's important. The energy transforms from one type into another and exists in more that one form at the same time. The extra EPE you gave the spring at the start when you stretched it is where this energy originally came from.
The KE the spring has as it passes the equilibrium point is used up in compressing the spring and raising its centre of mass a little higher.

A good exercise for you would be to identify which types of energy are present in the system at various points as the spring moves up and down. Include the top, bottom and mid point.
The system always has the same amount of total energy. That is KE + EPE + GPE
So if one increases another has to decrease.
At the equilibrium position initially there is no KE but some EPE (spring slightly stretched) and some GPE (depending on where you take zero for that.)
You then increase the total energy of the system by stretching the spring downwards.
When the spring rises and passes the equilibrium point, the system has KE in addition to whatever other energy was there at the start.

The 1st one is wrong.

The initial velocity is 4m/s as the balloon is descending.
So use u=4m/s not zero.
You should also state which equation you have used and not just an expression with numbers in it.
So for part 2 where did you get t = square root expression? from.

To do part two use the correct answer for v from part 1 and use v = u + gt to find t

In my textbook it says that leptons and antileptons can interact to produce baryons and antibaryons. Since leptons aren't made out of quarks or antiquarks I don't understand how they can interact to make baryons with quarks. Where do the quarks come from? Since quarks are fundamental particles they shouldn't be made out of leptons should they? I feel like this might be a stupid question but i don't understand the concept. If anyone could explain it to me I would be eternally grateful
Thanks

they wouldn't even spare you 20 quid a week as an investment in your future?

they are incomplete but i have some, they are written by me so may be a few mistakes in them. Not done kinematics, energy or the last bit of dc circuits.

Ill post them a few at a time, too big to post all at once! :)

The examiner will have the answers to the question in both cases. One using the accurate and one using a rounded value.
My own view is it is better to use the accurate intermediate result. You will not lose marks either way so long as you round to a sensible number of sig figs. Using 3 sig figs will be fine in most cases.
The way the exam paper works is that there will be one question where the use of sig figs is tested. This is the only question where you could lose one mark for using an inappropriate number.

AQA website

i got 30130.56 J/s after working out energy per second what do i do know

ya i did n my teacher said its alrite to exceed 1sf than the lowest sf in question anyways it should kept to lowest i.e in a given set of values say 25000 2135 21.2112 the answer during calulation would be to 2sf or 3 rite

So then is the correct answer 14.4503584207360145 ms? If it is, it does make some sense to select the answer in the choices which is greater then 14.4503584207360145ms and is closest to it since no air resistance is assumed and also the stunt rider would want to generally have a speed greater than minimum speed needed as a kind of safety net if that makes sense. So I guess it is reasonable to say that option 25.1ms should be chosen right?

But then the answer of 25.0846851ms with the incorrect method rounds to 25.1ms which is an option:confused:

Nice question OP

Ah, I was looking at the stagnation point for inviscid flow models (on right hand side). Cheers.

Ok, last one (plenty of questions here as I'm self-studying the unit, thanks for the answers, I appreciate it).

What's on the vertical axis of the graph? It has a label of an equation, but what does that equation stand for.

Also, I don't really fully understand those 3 major categories of high Re flow -- Subcritical, critical, and supercritical. I thought subcritical is pre-turbulent, critical is when turbulent flow starts to occur, and supercritical is turbulent flow occurring but looking at the diagram on LHS, all of them have turbulent flows. Could you explain those 3?

Okay just to clarify, when an electron is incident on an orbital electron it gives it energy of hf, so the electron is excited and moves up to a higher energy level, if this energy is sufficient enough it can cause ionization where the orbital electron will be released from the atom.

With photon absorption, where photons depends on frequency as this provides energy according to the equation of E=hf. There is a one to one interaction between an photon and the electron. The photon must have the exact amount of energy in order to excite the electron, thus the photon must be the same as the intial and final energy difference of the electrons. All of the electrons absorb the energy of hf, and these electrons occupy discrete energy levels


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Hey got this practice evalutive sheet but I am absolutely stumped on how to work out the percentage difference, For Q1) would it be 0.01/0.08 * 100 = 12.5%? But it is asking for the uncertainty in the cross sectional area so what can we do from here?

Q2) No idea what a worst acceptable straight line is, I would imagine it is different to the one shown and the diference in the y intercept/ normal y intercept * 100?

Q3) would it just be 1.08 x 10^-6 / 2.11 x 10^-6 * 100

Q4) Not reliable as no repeats not accurate as ?? no idea

Q5) Some errors but could somebody explain further?

please thanks for the help will + rep helpful answers. attached questions

Attachment 199799Attachment 199800

I asked my physics lecturer about some time-related topic and he asked me to find out about why there is a difference on the atomic clock when it is on a satellite than it is on earth.

I tried searching the net but many of the stuff I found mainly mentions about time dilation and they had to change the GPS settings to create the normal time flow, but not about why it happens.

So why?

Please & thanks. :):)

Incident means that it hits it- you use this to say "incident photons on a metal surface" as in, "photons hitting a metal surface"

When this collision happens, some energy is transferred from the incident electron (the electron hitting the atom) to the orbital electron in the hydrogen atom (the electron in the atom) which temporarily excites it to a higher energy level.
You might want to mention something about how for the electron to excite upwards, it must receive energy equal to the difference between ground state and n=2? Also, the excitation is temporary because the electron will eventually de-excite and emit that photon of characteristic frequency.

I don't know how many marks you're looking for, but I hope this helps!

the answer was, if we follow the assumptions set out in the OP, the ring would in deed float.

I think that if a metal hoop was given an inital spin, it would continue spinning owing to the induced eddy currents :)

Is the book for OCR A or OCR B?

sooo sorry couldn't reply you on time. :(

If we call a₀ the (arbitrary) initial radius and a₁ the altered radius, then the fractional increase in the field, f, is given by B₁/B₀, where B₁ is the field when a=a₁ and B₀ is the field when a=a₀.

If you calculate f at z=0 you get an expression for f in terms of a₁ and a₀.

Do the same thing for z>>a to get the factor at large z.

You can now eliminate a₀ and a₁ to express the factor at large z in terms of f.

The mass flow rate through the top is equal to the mass flow rate through the bottom since it is incompressible, therefore equate the top and bottom.

The mass flow rate can be expressed in terms of the density, velocity and cross sectional area (hint: it has units of kgs^-1).

I got 0.6m for the wavelength in part a i, I'm not sure whether I'm correct with part a ii, the wave moves twice (as shown with the dotted curve) and the period for one wave is 0.75 so I multiplied 2 and 0.75 to show the time period is 1.5, is this right?
But the main part I am stuck on is part b, mainly the first part with the calculations.

Using Stoke’s theorem and the identities given, ∇x∇(Scalar)=0 deduce the relationship between electrostatic field E and potential ψ at a point in space, show that E = -∇ψ


Does this question mean show a derivation which uses Stoke’s theorem and mathematical identities to obtain E = -∇ψ ?

Or is something else required since it states, "∇x∇(Scalar)=0 deduce the relationship between electrostatic field E and potential ψ at a point in space". I wasn't sure if by a derivation arriving at E = -∇ψ then in effect this would be illustrated.

Thanks

Sorry, I screwed up the LaTeX, but I just fixed it there!

I don't really understand quantum mechanics past a super, duper basic level so I can't answer your questions here!



They can have the same quantum numbers, as long as ALL of them aren't the same. e.g.

3,1,0, 1/2 and 3,1,0, -1/2 describe two electrons that are in the same p_y orbital. They have opposite spins - this is what prevents them being in the same quantum state.

They have lots of different quantum states simply because there's a lot of variability. I gave you the ranges there (which, I imagine, have been derived mathematically) that describes the permissive numbers depending on other variables.

n = energy level
l can be between 0 and (n - 1)
m_l = between -l and l in integer steps.
m_s = positive or negative one half.

Suppose n = 1; like in a hydrogen atom in ground state. Then the only possibly value for l is zero, therefore the only possible value for m_l is zero, but m_s is independent of the other states. Therefore a hydrogen atom can hold 2 electrons in its first shell/energy level.

Let's scale up to n = 2. Suddenly we have a big change:

n = 2
l = 0, 1
m_l = -1, 0, 1 for the l = 1 subshell.

Therefore 6 electrons.

Let's say we're looking at the electrons in n = 4!

n = 4
l = 0, 1, 2, 3
m_l = -3, -2, -1, 0, 1, 2, 3 in an l = 3 subshell

Therefore 14 electrons in the f orbitals (this is what you call the l = 3 subshell).

As you can see, you can have a large amount of variation within the properties of an electron in an atom.

How about the total number of electrons in a certain energy level? Well, you just have to compute all the values of l for a given n, compute all the possible ranges of m_l given the possible l's, and double that for spin.

So for n = 4, plug all the numbers through, and you have 32 electrons that can be in that one energy level. It's easy to see, then, how we can have lots and lots of electrons in an atom and not have any of them have the same quantum state.

Yep they can share quantum numbers - we know more than one electron can be in the same shell. The quantities above are related, as we kind of see it as there are the main electron shells (n), then each has a certain number of sub shells (l) and these two numbers are related - for a certain value of n, there are only a certain number of values for l. But within each sub shell, the electrons can differ in terms of orbital shape, and in terms of spin.

Looking at the most simple case, the ground state (lowest energy level), where n=1, we have to say l=0. So therefore m=0, but we can have two electrons in the ground state, one spin up, one spin down. So to answer your question, yes they can share the same quantum numbers, but have to differ on at least one - no two electrons can have exactly the same set)

(And this is why electrons fill different shells - it is as a result of quantum Physics and the Pauli exclusion principle) :)

Basically, this has to be a weak interaction, because you have a flavour change when a proton gets converted to a neutron i.e an up quark gets changed into a down quark through the emission of a W+ boson. The W+ boson then materialises the positive pion.

Hi,

There's a type of problem and I'm not entirely sure how to do it so if I give an example can someone post a solution (not allowed know but I've already handed it in and want to know if I did it right and if not how to do it as my tutor isn't the best at explaining stuff...)

In the first instance a positron collides with a stationary electron to produce a particle with rest mass 1200MeV, would I be right in saying that the energy that the positron must be accelerated to is 1200MeV minus the rest energies of the electron and positron?

In the second instance both the electron and the positron are moving towards each other, would the energy of each then be 600MeV?

Thanks.

I'd just change it slightly:

A varying voltage is applied to a piezoelectric crystal which makes it contract and relax at the applied frequency.
Ultrasound waves are produced (which are the same frequency of the contractions).
Ultrasound waves travel through various tissues or materials. Some of the waves are reflected at the boundaries where different materials meet. The reflected waves travel back towards the crystal, hit it, and cause it to vibrate at a new frequency. This vibration causes a varying stress which in turn induces a voltage. The time the wave took to be reflected, the amplitude and the frequency are calculated, so distances to each different material can be calculated and an image formed.

Hope this helps. It's a bit longer but could be shortened, but describes the process a bit more completely.

So if he did not compensate for the friction, the resultant force would be less than the applied force right?

You're right. Think of the circuit as a potential divider, with the parallel resistances forming the bottom part of the divider.

Now the p.d.s across both the thermistor and 1200 ohm resistor are always the same, since they're connected to the same points in the circuit.

So, if the total resistance of the parallel resistors is , then the voltage across them is:



This tends to 0 as tends to 0. But



which tends to 0 as (the thermistor resistance) tends to 0. So tends to 0 as tends to 0.

I have just been looking at a physics 6B (alternative to practical) past exam paper and I came across a question about heating a diode in a container of water.
After I tried answering it, I looked in the mark-scheme and it said that an indirect heat source should be used.

Would this be something like a tripod with gauze being heated by a bunsen burner, as the flame would not be directly onto the container with water and diode, it would be acting through the Gauze which would heat up and in turn heat up the container.

Any help appreciated,

Thanks,

Roars

thanks so no need to state anything about lenz's law?

Sorry dude, I really didn't mean any offence. I was just trying to help with the confusion. FTR, I thought you smashed that circuit question with a home run.

so does the area under a graph of stress vs strain represents energy density

Also how did you the the T actual value?

OK, so:

***
***

= 828 W = 830 W (2sf)

I understand you but the purpose of me attaching this question is to ask : "Can repeating be a method to increase accuracy" like in this question? some say no like in this thread but for example this question says yes leading to my confusion...
So it a method of increasing accuracy or not?!
thanks

Thank you!
Do you know how i would calculate the angle of release using trigonometry? Where would i get my data from? Thanks

The exam board only specify the knowledge of advantages in non-invasive techniques.

I can tell you they are specifically.
Less risk of infection
No trauma

Just two!

Nope, the search brings up A Level books or books on specific topics (quantum mechanics) only.

The book is kind of wrong with that example. Friction is proportional to the reaction force, this doesn't always equal the weight, but in this example it does. Think of it as the harder you press down on a surface the larger the friction becomes. You can test it with your finger now ;)

Friction has to have a limiting value because otherwise nothing could ever slip. It is to do with the coefficient of friction of the surfaces (obviously a smooth table will have a lower coefficient of friction to a rough road). The limiting value is basicaly the maximum force you can apply to something before it slips. You could think of it as being similar to how the floor can collapes under us if we have too large a weight :cool:

The equation of a transverse harmonic wave on a string may be written as:

y = 0.02 cos 2π (t -2x + 0.25)

find:

(f) the transverse displacement of a particle at t =1 s and x = 30 cm?

Here's values I've already worked out:

Amplitude = 2cm
Wavelength = 0.5m
Frequency = 1Hz
Velocity = 1ms^-1

I've worked out the answer to (f) to be -0.013m but in the answers it says -0.0118m is the right answer? Can someone explain where I went wrong?



Thanks in advance!

One last question if you had two resistors which had different values in parallel would the current in each resistor be different?


Posted from TSR Mobile

Sorry, i will attach an image of the question. Thank you for replying :)

Just to clarify, am I right in saying the precision is the smallest measurable value? So lets say if you have a voltmeter reading of 4.68 V then the precision is 0.01 ? That's what this video says anyway:

http://www.youtube.com/watch?v=1dTn2pt5PuA

But in my first post I stated that the precision is 0.5 mm.. Which one is correct?

Also, if the precision is 0.5mm does it mean the uncertainty is ±0.5 ?

Name three isotopes that have similar half lives

http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20 and%20AS%20Level/Physics%20(9702)/9702_w10_qp_42.pdf


http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20 and%20AS%20Level/Physics%20(9702)/9702_w10_ms_42.pdf

How come the increase in internal energy is 240? I don't get it

Please help, I don't get the graph at all

I'll try my best

Stress= force/cross sectional area

Tensile stress is when you apply a force on a material and the material is under tension and is pulled apart.

Compressive stress is when you apply a force on a material and the material is under compression.

Strain= change in length/original length

Tensile strain is an increase in length when the material is under tension and is pulled apart.

Compressive strain is a decrease in length when the material is under compression.

:)

Strange as it may seem, the charge on series capacitors is equal, no matter what their capacitance.
(Think that the current through series resistors is the same no matter what their resistance.)
The charge on any one of the series capacitors is equal to the charge on the equivalent capacitor you get by combining them in series.
That's why they use the charge calculated on the equivalent capacitor as being also the charge on the individual capacitor.

This might help a bit.
http://hyperphysics.phy-astr.gsu.edu.../capac.html#c2

http://papers.xtremepapers.com/CIE/C..._w10_qp_42.pdf

Please help, I don't get how it stays 240 for P to Q and the whole table is confusing

http://papers.xtremepapers.com/CIE/C..._w10_ms_42.pdf

For simplicity, do we just ignore the fact that momentum is negative? Or do we not use conservation of momentum?

The wiki page explains this ok. There is even a picture of the coma round the head of the comet.
http://en.wikipedia.org/wiki/Coma_(cometary)

Hi sorry i know this is off topic but what is meant when a fully charged capacitor is discharged through a resistor with a time constant of 0.2ms?

is it thaat the charge will fall to 37% of its original value in 0.2ms? if it is why is it correct? to me it seems right but i dont know why!? :(

Thank you

PS your other explanation helped a lot!

Hiya guys !


I've carried out a practical in which we measure the gravatational potential energy of a ball when throwing it from a set height and then recording the height it bounced back at. I've done all my data on kinetic energy and gpe. just stuck on working the efficency


So what is my energy input and energy output?

Yes I used t=1 and t=5 and i got the x component to be the same, but the x component is space isn't it? In order for an event to be simultaneous doesn't the time component need to be the same?

That was ABSOLUTELY DYNAMITE!! Best post I've read on TSR!

You literally tripled my understanding of Electricity with that, my future A is dedicated in your honour, sir!!

(My reps are on recharge but they're sure as hell coming your way.)

Would you be able tobexplajn this diagram. I don't get the deal with thw arrows of fission and fusion. When the arrow ends, does that mean fusion/fission cant happen anymore?
Also there was this question asking why fission of heavy nucleus is likely to release more energy than a pair of light nuclei undetgoing fusion.
Is it because the fission arrow os longer?

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I don't get how you calculate the frequency of spectral line B by just looking at that diagram, can anyone help me out, it question 5a part i, here's the link to the paper:

http://www.tomred.org/uploads/7/7/8/..._june_2006.pdf


Posted from TSR Mobile

How would you go about answering the question how many traffic lights are there in london? Or how many windows are there in london?

According to Special relativity, when we observe objects moving in a different reference frame, do we observe them moving faster or slower than the 'proper speed'?

When I substitute the equations for time dilation and length contraction, I get the proper velocity as holding two different possible values. (one being negative)

The LH and RH rules don't deal with electrons.
The RH rule and LH rule are based on "conventional" current, which is always the flow of positive charge. (The rules date back to the time before the electron was discovered!)
If you want to know the direction of flow of electrons or negative charges you just take the opposite direction to that of the positive charge.
The LH rule is used for working out the direction of the force on a conductor carrying a current in a magnetic field. For this reason it is often called the "motor" rule.
The RH rule is used for finding the direction of the induced emf (and current if it can flow) when a conductor is moved through a magnetic field. Because it deals with the creation of emf and possibly current it is often called the "generator" or "dynamo" rule.
You are quite right that the rod could hardly be described as a generator in this situation. The point is that there is an emf generated in it, so you use the RH rule. Agreed, this emf is not of much use because there is no circuit for the current to flow in, but that is beside the point.

Still don't get it,

Now what....

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Hi for single slit diffraction, double slit diffraction and diffraction gratings what happens when you increase and decrease the slit width?

Also the equation for double slit is
w= (wavelength x D) / s

and diffraction grating
dsinx=n(wavelength)

My second question is are s and d in the two equations the same thing (distance between slits)?
Also is this the same thing as slit width. Or are slit width and distance between the slits two different things?

Thanks in advance :)

You're going to kick yourself when you see what you forgot. Remember that

So SI base units are like seconds, metre, amperes etc

Derived SI units e.g. joule, watt, newton, are built using a combination of SI base units.

Power and time are just quantity names right?
Thanks

In order for the scale reading to increase the magnet has to push down on the pan.
In order for the magnet to push down on the pan, it has to push up on the wire.
If you were standing on the pan and you had a rail near your hand, which way would you push the rail, up or down, in order to make the reading of your weight larger?
Yes, it is about Newton's 3rd Law. If you push something upwards, it pushes you downwards.

I calculated it to be 723 so i got the point ( much more that background can be neglected) right?
Plus another question if not too much in the other attachment I just uploaded I know how to do the experiment and everything but in the precautions one of the answers was that the amplitude or displacement should be small. Can you please tell me why is that? THANKS ALOT

the rate meter calculates and displays an average rate as it goes, the scaler just does a count.

tbh it was a bit more obvious what was going on with the oldskool analogue ratemeters, the needle jerked up the scale rapidly with every 'click' but fell back more slowly between - thus averaging out the random events.

Hi there,

Really struggling with this mock question - think it has something to do with Newton's Second Law but can't find an example anywhere. Any help/advice would be much appreciated.

A plane of mass 30 tonnes has landed and is slowing along a runway. Its engines are supplying a retro thrust of 20 kN and air resistance is 35 kN. What is the plane's deceleration?

Thanks,

Fred

Yes if R was 1 ohm. It depends on R, of course.
A value of R was not provided in your posts, but the whole point here is the relative size of R compared with the impedances of the other components.
You asked for a non calculation answer so you have to answer in general terms. Assuming a value of R is not really in the spirit of "non calculation". :)
Can I also say that it is much easier for us to answer questions when they are posted in their entirety, rather than just part questions or the poster's paraphrase of the question.
Anyway, you have your answer now. Yes?

Thanks, I thought I had marked her answers.

2. B
3. B or E
4. A

Can you confirm this is right or wrong?

whoopsy! my bad! :D

Go through the textbook and make sure you know the ins and outs of all the experiments that they describe.

Look at previous papers' mark schemes to see what kind of things you get marks for, and when writing your answer make sure you try to answer each point as clearly as possible.

Don't forget to mention doing repeat readings and plotting a graph (when you mention a graph, explicitly state the dependent and independent variable, as well as what the gradient and/or area under the graph represent.

I dont get it ,what do u mean?


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