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A2 6PH04 Physics Unit 4 'Physics on the Move' - 11th June 2012

Reply 120

Alexok

8

I have a feeling principles of detection/analysing detections and maybe transformers will come up

Reply 121

Alexok

8

Original post by Estelle123

whats an electron neutrino?! infact wth is a neutrino?!

All need to know is that a neutrino has no charge. Anythig with a *blablabla neutrino* has no charge so will not show a path in a bubble chamber etc

Reply 122

dzone25

I am NOT having a good time right now... Can't seem to do anything without making a stupid mistake :frown:

Really hope transformers come up because they're easy but what else is likely? I need to focus my revision a bit its not going too well... Any tips?

Edit: I missed a bunch of lessons about electric field and all that sort of topics... Any notes would be appreciated as its hard to get my head round like Jan 2012 Q12

(edited 11 years ago)

Reply 123

d_94

7

Original post by dzone25

I am NOT having a good time right now... Can't seem to do anything without making a stupid mistake :frown:

Really hope transformers come up because they're easy but what else is likely? I need to focus my revision a bit its not going too well... Any tips?

Edit: I missed a bunch of lessons about electric field and all that sort of topics... Any notes would be appreciated as its hard to get my head round like Jan 2012 Q12

Principles of detection/ analysing detections, transformers, circular motion

Reply 124

astaraeal

1

Original post by dzone25

I am NOT having a good time right now... Can't seem to do anything without making a stupid mistake :frown:

Really hope transformers come up because they're easy but what else is likely? I need to focus my revision a bit its not going too well... Any tips?

Edit: I missed a bunch of lessons about electric field and all that sort of topics... Any notes would be appreciated as its hard to get my head round like Jan 2012 Q12

Jan 2012 Q12 is about the production of magnetic fields by electric charges - a stationary electric charge produces an electric field, a moving electric charge produces a magnetic field.
If you have two objects both producing magnetic fields and their magnetic fields interact, the objects will either attract or repel each other.
For this question, the two wires have currents travelling in the same direction, so you can work out the direction of the magnetic field using the right hand rule (point your thumb in the direction of the current and your fingers curve in the direction of the magnetic field). If you get a friend and both of you place your right hands next to each other, you can see that your fingers point in opposite directions in between your hands - so the wires attract as the magnetic fields between them are in opposite directions, and each wire is in the magnetic field produced by the other wire.
You can also look at this from the point of view that there is a current-carrying wire in a magnetic field, so by Fleming's LHR, it experiences a force towards the source.
Finally, because there are two magnetic fields, there will be a neutral point between the wires where the fields cancel :smile:

Reply 125

dzone25

Original post by d_94

Principles of detection/ analysing detections, transformers, circular motion

But didn't detection come up in Jan 2012?

(I'm seriously hoping alpha particle scattering comes up again xD free marks)

Transformers are well easy enough just one formula? Circular motion isn't TOO hard considering I have to do M3

What gets me is the longer questions, I know what to write but sometimes they give marks for the most stupid things (like current in a wire produces a magnetic field ... Well duh?)

Reply 126

astaraeal

1

Original post by dzone25

But didn't detection come up in Jan 2012?

(I'm seriously hoping alpha particle scattering comes up again xD free marks)

Transformers are well easy enough just one formula? Circular motion isn't TOO hard considering I have to do M3

What gets me is the longer questions, I know what to write but sometimes they give marks for the most stupid things (like current in a wire produces a magnetic field ... Well duh?)

They tend to try and cover as many specification points as possible, so alpha particle scattering could show up *crosses fingers*

And I tend to state the obvious stuff first and then elaborate - it's not a perfect strategy though!

Reply 127

naveeshan

Original post by whooshpaddy

Most important to know momentum in more than one dimension, circular motion, electric fields, magnetic fields, emf, motors and transformers, particle acceleration and detection.

I predict questions on transformers, momentum in 3d and circular motion.

What does momentum in 3D exactly mean...Do you mean resolving the velocities in one direction and then using momentum conservation?

Reply 128

EllaBella<3

12

I would be really grateful if somebody could just confirm something for me! :smile:

With capacitance, as the capacitor charges, the voltage across it increases until it reaches the terminal voltage? Is this correct? Is this why the current decreases?

Also, i've got a question that says "as the coil rotates faster the current in it reduces" Explain this observation. Is this because as it rotates faster, flux is cut at a greater rate therefore the emf and voltage increases therefore the current decreases?

I hate electricity .. :L

Reply 129

Karisliana

Original post by naveeshan

What does momentum in 3D exactly mean...Do you mean resolving the velocities in one direction and then using momentum conservation?

Yes, can anyone post a worked example please as I find them really difficult :smile:

Reply 130

astaraeal

1

Original post by EllaBella<3

I would be really grateful if somebody could just confirm something for me! :smile:

With capacitance, as the capacitor charges, the voltage across it increases until it reaches the terminal voltage? Is this correct? Is this why the current decreases?

Also, i've got a question that says "as the coil rotates faster the current in it reduces" Explain this observation. Is this because as it rotates faster, flux is cut at a greater rate therefore the emf and voltage increases therefore the current decreases?

I hate electricity .. :L

See my post on the previous page for an explanation of the back emf in a motor :smile:

As for capacitance, the potential difference across a capacitor increases as it charges because there is a flow of electrons around the circuit from one plate to the other, so as the difference in charge builds up, so too does the potential difference.
This means that the potential difference across the resistor falls, as in a series circuit, total pd is shared between components, so V=V(capacitor) + V(resistor) and increasing V(capacitor) decreases V(resistor). As V=IR, and the resistor has constant resistance, decreasing V decreases the current. When V(capacitor) = total circuit V, V(resistor) = 0 so I = 0.

Reply 131

Estelle123

2

can anyone explain to me q5 multiple choice june 2011 about the car on the hump-back bridge? you had to say what the force is on the car from the bridge when the car is at the top of the bridge. (the answer is mg-mv^2/r)

Reply 132

astaraeal

1

Original post by Estelle123

can anyone explain to me q5 multiple choice june 2011 about the car on the hump-back bridge? you had to say what the force is on the car from the bridge when the car is at the top of the bridge. (the answer is mg-mv^2/r)

If you look at the forces acting on the car, there must be a resultant centripetal force acting on it at the top of the bridge to keep it moving in a circle, so the resultant force acting on it is mv^2/r. The two forces acting on it are its weight, mg, and the normal reaction from the bridge, R.
This gives mg-R = mv^2/r (the resultant force is down towards the centre of the circle so mg > R.)
Rearranging, R = mg - mv^2/r as required :smile:

Reply 133

naveeshan

Original post by EllaBella<3

I would be really grateful if somebody could just confirm something for me! :smile:

With capacitance, as the capacitor charges, the voltage across it increases until it reaches the terminal voltage? Is this correct? Is this why the current decreases?

Also, i've got a question that says "as the coil rotates faster the current in it reduces" Explain this observation. Is this because as it rotates faster, flux is cut at a greater rate therefore the emf and voltage increases therefore the current decreases?

I hate electricity .. :L

As the capacitor charges the voltage across it increases and the voltage across the resistor decreases.Since the resistance is a constant and according to V=IR the current decreases.

As the coil rotates faster there is a rate of change of magnetic flux linkage according to Faradays law.But according to Lenzs law the induced emf opposes the change causing it and in this case the change causing it is current and thus it decreases.

Hope it helps you :smile:

Reply 134

EllaBella<3

12

Do we need to know the charges on quarks?

Reply 135

astaraeal

1

Original post by EllaBella<3

Do we need to know the charges on quarks?

Only on the up quark (+2/3e) and the down quark (-1/3e). Anything else should be given :smile:

Reply 136

EllaBella<3

12

Original post by astaraeal

Only on the up quark (+2/3e) and the down quark (-1/3e). Anything else should be given :smile:

Thank you - I saw a question and it didn't give it to you, I was having a panic that I was going to have to learn a bunch of numbers .. less than 24hrs before the exam! :L

Reply 137

astaraeal

1

Original post by EllaBella<3

Thank you - I saw a question and it didn't give it to you, I was having a panic that I was going to have to learn a bunch of numbers .. less than 24hrs before the exam! :L