0
\$\begingroup\$

This is a homework question that I have stuck for a while and couldn't able to come up with the correct answer.

So here is the question,

enter image description here

My thoughts towards this question

  • When I move the rod PQ with a constant velocity ,the area of triangle RPQ inside the magnetic field increases .
  • Once the area inside the magnetic field increases E.M.F induces also increases.
  • Since induce E.M.F get increased the induced current should also be increased.

So according to my arguments I choose the answer as the third one. But the answer in marking scheme is the first one.

What I have done wrong. Please explain this question with details.

\$\endgroup\$

2 Answers 2

Reset to default
2
\$\begingroup\$

The question asks for the current, not the voltage.

The voltage (emf) generated would follow a straight line (not a curve) as the rate at which the area grows is proportional to the length of the wire - and the length of the wire grows linearly.

The current that flows as a result of this depends on the resistance of the loop. The circumference of the loop grows linearly with the horizontal position of the wire (similar triangles - when the wire has moved twice as far to the right, all the sides are twice as big).

The current is voltage divided by resistance. Both grow linearly; their ratio is constant.

\$\endgroup\$
14
  • \$\begingroup\$ Please floris explain little bit more , specially the theory parts I want to use . A kind request \$\endgroup\$
    – On the way to success
    Jun 30, 2015 at 14:47
  • \$\begingroup\$ your first two bullet points are exactly right, but then you need Ohm's Law: I = V / R. And R scales with the length of the wire, just like V did. There is really nothing more to say. \$\endgroup\$
    – Floris
    Jun 30, 2015 at 14:49
  • \$\begingroup\$ I think ,we need to move this to a chat, isn't it? \$\endgroup\$
    – On the way to success
    Jun 30, 2015 at 14:50
  • \$\begingroup\$ Because I have confused with some facts \$\endgroup\$
    – On the way to success
    Jun 30, 2015 at 14:50
  • \$\begingroup\$ Or please explain this with more , like you did in previous questions.You helped me lot Mr.floris \$\endgroup\$
    – On the way to success
    Jun 30, 2015 at 14:55
1
\$\begingroup\$

The voltage (or EMF) between P & Q is a constant given constant length, velocity and magnetic field, lets call it V.

The voltage between R & S is RS/PQ V, the induced current is through RBQ is equal to RS/PQ V/R by Ohms law.

Let L be the distance to the right of B that the wire is.

RS=2Ltan30

Assuming constant resistivity in the wire (r),

R=4Lrtan30

So, I = 2Ltan30/PQ V / 4Lrtan30 = V/2PQr

Which is independent of L

\$\endgroup\$
1
  • \$\begingroup\$ Could you explain this little bit more ? \$\endgroup\$
    – On the way to success
    Jun 30, 2015 at 10:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.