Two metallic wires are lying parallel, if current is in these wires be flowing in same direction, so these wires will……….

Two metallic wires are lying parallel, if current is in these wires be flowing in same direction, so these wires will ................( Attract each other ). 

Because 

If wires are parallel and current is flowing in same direction , so magnetic field will be according to right hand rule. 

 Right hand rule : 

    Right hand rule says that if the thumb is showing the direction of current flowing , so our fingers will show the direction of magnetic field. 

So at that point , one wire has positive pole and the other one have negative pole.So as the positive and the negative pole will attract each other. So by that wires will also attract each other. 

If we consider against of this:-

If two wires are parallel but current is flowing in opposite direction , so wires will:-

If the current is flowing in the opposite direction of  the parallel lines, so the magnetic field will become like as shown in the figure . So the same poles ( positive positive or negative negative ) will get generate a point  and the poles will repel each other . As similar the wires will also repel each other .

2 )  Fundamental frequency of stationary waves in an open pipe as compared in frequency of a closed pipes is …………… ,

A ) Remains Same ,                                        B ) Two times ,

C ) Three times ,                                              D ) None of these ,

Correct Answer : -     B ) Two times ,

Because in close pipe we have frequency at first harmonic :-

f_c =  v / λ   ,                      and   for close pipe  ,   λ  is 4L .     So ,

 f_c = v / 4L   ,             And we can also write it like this ;

 4f_c  =  v / L  .………….. eq. ( 1 )            ( For Closed pipe ) .

So , For open pipe , we have frequency at first harmonic : -

 f_o = v / λ  ,                     and  for open  pipe ,   λ  is 2L  .    So ,

f_o =  v / 2L .               And we can write it like this ;

2f_o  =  v / L  ..…… eq. ( 2 )            ( For open pipe ) .

So ,        equation 1 = equation 2     ,

So ,           4f_c   =  2f_o                ,

Then ;          (4/2)f_c   =  f_o                   ,

So               2f_c   =  f_o          OR           f_o = 2f_c   .

So , Its is shown that frequency for open pipe is 2 times the frequency in closed pipe .

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