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The expression epsilon=(-dphiB)/dt Th...

The expression `epsilon=(-dphi_B)/dt`
The negative sign indicates the direction of E and current in a closed loop
II. The negative sign indicate that fiux due to current I (because of e) is opposite to change in `phi_B`. Which of the above statements) is/are correct?

A

Both I and II are incorrect

B

I Is correct, II Is incorrect

C

I Is Incorrect, II Is correct

D

Both I and II are correct

Text Solution

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The correct Answer is:
D
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Magnetic flux phi_(B) through a plane of area 'A' placed in a uniform magnetic field vceB is given as: phi_(B)= vceB.vceA = BA cos theta where theta is the angle between vceB and vceA . The above relatio can be extended to curved surfaces and non-uniform fields. In general, if the magnetic field has different magnitudes an directions at various parts of a surface, then the magnetic flux through the surface is given by phi_(B)=int vec B.dvecA On the basis of the experimental observations, Faraday concluded that an emf is induced in a coil when magnetic flux through the coil changes with time. Faraday stated his conclusions in the form of a law called Faraday's law of electromagnetic induction. As per this law, the induced emf is given by varepsilon = -(dphi_(B))/dt The negative sign in the expression indicates the direction of induced emfe and hence the direction of current in a closed loop. In the case of a closely would coil of N turns, change of flux associated with each turns is the same and so that total induced emf is given by varepsilon=-N(dphi_(B))/dt From above relations it is clear that the magnetic flux can be changed by changing any one or more of the terms vceB, vceA and theta . (a) Give SI unit of magnetic flux. (b) How is it related to tesla ? (c) Obtain dimensional formula of magnetic flux. (d) A loop of area 4 xx 10^(-3)m^(2) is placed with its plane perpendicular to a uniform magnetic field of 0.02 T. If the loop is quickly removed from the magnetic field within a time of 2 ms, what is the magnitude of induced emf across the two ends of the loop ? (e) If the resistance of the loop be 0.2Omega and a sensitive milliammeter be connected between the two ends of loop, what will be the reading of milliammeter?

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Knowledge Check

  • Identify the correct statement I. The flux can be altered by changing the shape of a coil in a magnetic field or rotating coil in a magnetic field such that the angle between B and A changes. II. By changing the shape of a coil or the angle between B and A, an emf is induced in the coil. Which of the above statement(s) is/are correct?

    A
    only I
    B
    only II
    C
    Both I and II
    D
    Neither I nor II

  • Figure shows a square loop carrying current I is present in the magnetic field which is given by vecB=(B_(0)z)/(L)hatj+(B_(0)y)/(L)hatk where B_(0) is positive constant. Which of the following statement(s) is/are correct?

    A
    force on side (0,0) to (0,L) is `((B_(0)IL)/(2))hati`
    B
    force on side (0,L) to (L,L) is `-B_(0)ILhatj`
    C
    Net magnetic force on loop is zero
    D
    force on side (L,0) to (0,0) is zero

  • The expression for the induced e.m.f. contains a negative sign [e=-(dphi)/(dt)] . What is the significance of the negative sign?

    A
    The induced e.m.f is produced only when the magnetic flux decreases.
    B
    The induced e.m.f opposes the change in the magnetic flux.
    C
    The induced e.m.f. is opposite to the direction of the flux
    D
    None of these

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