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kindly refer to the attachment. I have mentioned where exactly I have the doubt in the attachment

kindly refer to the attachment. I have mentioned where exactly I have the doubt in the attachment 

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Grade:10

1 Answers

M H Rashid
35 Points
6 years ago
We cannot find the resultant velocity of the -ve and +ve charged ions. Let me clarify your concept first.
When a single paticle has two or more velocities then we talk of the resultant velocity of that particle, and when two or more particles are moving then we talk of the velocity of the centre of mass of the system of particles.
Example 1: A man crossing a river in still water has one velocity (let V1). When he does not want to cross the river and only floats, his velocity is equal to the velocity of water current (V2) – this is the second velocity. Now when he tries to cross a flowing river – he has both the velocities V1 and V2 simultaneously –– the first across the river and the second along the river. In this case we talk of the resultant velocity of the man.
Example 2: When two or more particles are moving, we talk of the velocity of the centre of mass of the system of particles. We do not talk of the resultant velocity in this case.
YOUR PROBLEM: Now it is clear that even if they move in opposite directions, there is nothing like resultant velocity of the two charged particles. Instead we find the current contributed by the flow of the two ions separately and add them up.
I=I1+I2
I1=neAv and I2=n(2e)A(v/4)=(1/2)neAv
So, I=(3/2)neAv      Answer is D.

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