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A wooden stick of length 3l is rotated about an end with constant angular velocity \omega in a uniform magnetic field B perpendicular to the plane of motion. If the upper one third of its length is coated with copper, the potential difference across the whole length of the stick is

 

                        

 

Option: 1

\frac{9\; B\; \omega l^{2}}{2}         


Option: 2

\frac{4\; B\; \omega l^{2}}{2}


Option: 3

\frac{5\; B\; \omega l^{2}}{2}


Option: 4

\frac{\; B\; \omega l^{2}}{2}


Answers (1)

best_answer

 

Motional E.m.f due to rotational motion -

Conducting rod \rightarrow

\varepsilon =\frac{1}{2}Bl^{2}\omega =Bl^{2}\pi\nu

 \nu \rightarrow f\! r\! equency

T \rightarrow Time\; period

 

- wherein

 

 

When the rod rotates, there will be an induced current in the rod. The given situation can be treated as if a rod 'A' of length '3l' rotating in the clockwise direction, while another say rod  'B' of length '2l'  rotating in the anti clockwise direction with same angular speed '\omega'.

As we know that e=\frac{1}{2}B\omega l^{2}

For 'A' : 

e_{A}=\frac{1}{2}B\omega \left ( 3l \right )^{2}          &        e_{B}=\frac{1}{2}\; B\left ( -\omega \right )\left ( 2l \right )^{2}

Resultant induced emf will be :  

e=e_{A}+e_{B}=\frac{1}{2}B\omega l^{2}\left ( 9-4 \right )                    e=\frac{5}{2}B\; \omega l^{2}

Posted by

Rishi

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