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Physics: Post your doubts here!

taffycandy

taffycandy

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hey can u help me with this question
Q) a certain charge Q is dived into two parts q and Q-q,which are then separated by a certain distance.what must q be in terms of Q to maximize the electrostatic repulsion between the two charges?
Q)
two free particles (that is,free to move )with charges +q and +4q are at distance L apart . A third charge is placed so that the entire system is in equilibrium is unstable.
 
mehria

mehria

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mahabaloch said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s03_qp_1.pdf
someone please help me with Q20 and 32
Click to expand...
Q20:- As:- P=ρɡɦ
Where P= pressure
ρ= Density
ɦ= height
So:- ɦ= p/ρɡ
And 10% of p0 is multiplied with the equation

h=
C:\Users\user\AppData\Local\Temp\msohtmlclip1\01\clip_image004.png
p0 x p/ρɡ = p0/10ρɡ

Q32:- Whenever u are asked to find the Current in a circuit then always use terminal voltage instead of e.m.f of battery..as some of the voltage is used up by the internal resistor
i.e. I= V/R = 7.5/15= 0.5A
 
S

sagar65265

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taffycandy said:
hey can u help me with this question
Q) a certain charge Q is dived into two parts q and Q-q,which are then separated by a certain distance.what must q be in terms of Q to maximize the electrostatic repulsion between the two charges?
Q)
two free particles (that is,free to move )with charges +q and +4q are at distance L apart . A third charge is placed so that the entire system is in equilibrium is unstable.
Click to expand...

Q1) Suppose the particles are separated by a particular distance x, and their charges are as you have mentioned, one with a charge "q" and another with charge "Q-q".

Then, the coulomb force acting between them would be equal to:

F(Coulomb) = kq(Q-q)/x^2

Now, we want to know what values of q (in terms of Q) will result in the greatest force on each. Therefore, we want to find the maximum value of F(Coulomb) as q varies.

Therefore, we take the derivative of F(Coulomb) with respect to q and equate that to zero as follows:

d[F(Coulomb)]/dq = kQ/x^2 - 2kq/x^2

Setting this to zero, we get kQ/x^2 = 2kq/x^2
Cancelling out k and x^2, we get:
Q = 2q
q = Q/2

Substituting this value into the equation for F(Coulomb) we get
F(Coulomb) maximum value = kQ^2/(2x^2) Newtons

Q2) I can't really understand this question; is the final situation supposed to be stable or unstable? What is the magnitude of the charge to be placed between the +q and +4q charges?

Good Luck for all your exams!
 
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