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Electricity

Blazing goIITian

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19 Jul 2008 00:31:28 IST

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Urgent. helppppp

None

Q1) When no current passes through a conductor, why is the average of velocities of all the free electrons at an instant is zero????

Q2) Find R in the given figure....

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Anant Kumar

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21 Jul 2008 00:31:47 IST

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Re:Urgent. helppppp

Anant Kumar

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21 Jul 2008 00:34:12 IST

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When no current flows in a wire, the charge carriers have random velocity because of thermal agitation. The direction of the velocities is random and when averaged over the entire collection of particles, it add up to zero.

reddevil_2009

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21 Jul 2008 00:40:23 IST

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SIR U ARE GR88888

Anant Kumar

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21 Jul 2008 00:42:17 IST

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thanx :)

anchit saini

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21 Jul 2008 22:01:38 IST

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A very , very easy approach to this would be nodal analysis

Considering the top leftmost point at 0 potential , then the distribution is as shown

However its given that 120 - X =100

hence , X =20

Also , since the right 2 resistors are in parallel the sum of currents that flows through them individually = current flowing through 10 ohm resistor

[120-20]/R + [120-20]/100=[20-0]/10

which gives R =100

snail

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21 Jul 2008 22:32:56 IST

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Both the approaches above are correct and informative.

We can do like this also:

Current through 10 ohm=(120V-100V)/10 ohm = 2A

Current through 100 ohm=100V/100 ohm =1 A

So current through 'R' = 2A - 1 A= 1 A

ie. R=100V/1 A= 100 ohm

Basically it is all same!

reddevil_2009

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22 Jul 2008 23:50:52 IST

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very good anchit..........easy and quick......

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