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BITSAT 2018
Exam
BITSAT
Year
2018
Subject
Physics
Chapter
Magnetic Effects of Current

BITSAT 2018 · Physics · Magnetic Effects of Current

A copper rod of mass m slides under gravity on two smooth parallel...

A copper rod of mass mm slides under gravity on two smooth parallel rails ll distance apart and set an angle θ\theta to the horizontal. At the bottom, the rails are joined by a resistance RR in figure. There is a uniform magnetic field BB perpendicular& to the plane of the rails. The terminal velocity of rod is

A copper rod of mass m slides under gravity on two smooth parallel rails l distance apart and set an angle θ to the

Options

  1. A

    mgRtanθB2l2\dfrac{mgRtan\theta}{B^{2}l^{2}}

  2. B

    mgRcotθB2l2\dfrac{mgRcot\theta}{B^{2}l^{2}}

  3. CmgRsinθB2l2\dfrac{mgRsin\theta}{B^{2}l^{2}}
  4. DmgRcosθB2l2\dfrac{mgRcos\theta}{B^{2}l^{2}}

Correct answer

C. mgRsinθB2l2\dfrac{mgRsin\theta}{B^{2}l^{2}}

Step-by-step solution

Terminal velocity of the rod is attained when magnetic force on the rod (Bil)& balances the component of weight of the rod(mgsinθ),( mgsin\theta ) , as in figure.

A copper rod of mass m slides under gravity on two smooth parallel rails l distance apart and set an angle θ to the

So, Bil=mgsinθBil = mgsin\theta

B(eR)l=mgsinθB\left(\dfrac{e}{R}\right)l = mgsin\theta

BleR=mgsinθ\dfrac{Ble}{R} = mgsin\theta

Bl(B/VT)R=mgsinθ\dfrac{Bl\left(B / {V}_{T}\right)}{R} = mgsin\theta

vT=mgsin\thetaRB2l2{v}_{T} = \dfrac{mgsin\thetaR}{B^{2}l^{2}}

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