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A2 Physics | Post your doubts here

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June 2004
Question 4 c)
Larger surface area, therefore larger air resistance causing drag which acts as a damping factor reducing the amplitude of oscillations.
Question 6:-
Thermal energy was required to break some intermolecular force.
There was no work done since it doesnt expand much, hence it does not push on the atmosphere as much as boiling does.
Question 8 B iii)
Neutrons dont have any binding energy since they are already alone, hence they are not included in calculations.
 
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June 2006
Question 2 b iii)
This is a tricky question. First of all you need to find the volume of gas in the Cylinder by the eqn P1V1=P2V2.
The trick is that you have to know that the cylinder has to have the same initial amount of volume inside it or else it will collapse due to atm pressure.
After you find the V2 ( which is the volume of the gas in the cylinder at ballon pressure) , deduct 4x10^4 from it and divide by the volume of one ballon.
Question 6 c) + Question 7
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November 2006
Question 3 c:-
Remeber June 2004 Question 4 c)?
Question 6 a ii)
It blocks the negative values of ac current. Half wave rectifier. So when pd across diode is maximum (Vnode) then the resistor will have zero volts.
 
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June 2007
Question 3 d) i)
Fair enough :)
Question b ii)
Attachment
Question 7 b)
The Voltage is fixed since it is determiend by the rate of change of flux.
Higher resistance, means less Induced Current since R=V/I.
Less induced current means less energy loss by motor effect, therefore less damping. P = V x I or P = V^2 / r but you cant use P = I^2 R since the current changes x2!
If you do this in an open circuit. Resistance is maximum , current is zero, so no damping.
Question 7 c iii)
Usefull:- child swinging when you push him at the resonant frequency, microwave heating by resonance of hydron nuclei in food, plucking of a guitar string.
Avoid :- bride resonance by wind or people or cars, buildings during earthquackes causing them to collapse.
 

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Novemer 2007
Question 1 b i )
Centripetal force is the resultant. Here there is no tension because it is an ELASTIC string. So Fc = 5 Newtons which is the weight.
Find omega by m x r x omega^2 = 5!
Question 4 b)
Tangential to the electric field line and opposite in direction since the field lines represent the direction of the force on a positive charge by definition.
Question 4 c) iii)
It will be negatively charged by induction. Potential will be smaller because there will be less work in moving the charge since now we have an electric field between 2 surfaces.
Question 4 d)
Gravitational forces are always attractive i.e negative in value, so anything in between the fields should be attracted by both. But electric forces can repel positive charges.
Question 5 bii)
All the area under the curve, you can do that by counting / estimating the number of 1 cm^2 squares then multiplying by the area of one.
 
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Feel free to post any more questions :) More than glad to help! Just doing my duty as a brother :D
Now I can't get my head around Question 9, June 2009! Got too bored thinkin about it...
 
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Was explained to XPFMember, Thermal energy is required to increase the electric potential of the particles by breaking some intermolecular forces.
But there is no work done against the atmosphere unlike boiling and the volume change when melting ice is significantly small.
Therefore q increases, and w doesnt . Meaning The Internal Energy Increases !
 
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hey guys... i'm doing electromagnetic questions, and there's this equation 'B= 2x10-7 x I/x'

Where the heck is this equation from? :O

and what is 2x10-7 supposed to be :(
 
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hey guys... i'm doing electromagnetic questions, and there's this equation 'B= 2x10-7 x I/x'

Where the heck is this equation from? :O

and what is 2x10-7 supposed to be :(
2*10^-7 is the force betwee n the wires carrying curent of 1 A and distance b/W them is 1 m................
 
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Unless someone answers it, I will be solving 2010 tomorrow.

Attachment!
P.S:- 0.05 percent silver = 5 g out of 100g
0.95 percent gold = 95 g out of 100g
Ok bro, no one will its already a week since i posted!
 
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