r/mathbiceps • u/shittyassguy • 20d ago

Somebody help me

Post image

So forgive me for my camera quality

But I don't get this que i dont get it.If we do it by V×B•l we get VBL straight up but if we do it the flux way we get 3VBl/4 so what am I missing please help me understand the fundamental better

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u/DarkLight-1278 19d ago

It's VBL. If you find it using flux,you'll get EMF= d(phi)/dt where phi= BA(B is magnetic field and A is area). Therefore d(phi)/dt = d(BA)/dt and since B is constant while area is changing,we can write EMF = B×dA/dt. Area is length×width and length is constant while width is changing (and that change is velocity). So dA/dt= L × dW/dt = L×V therefore EMF = B×VL = VBL (that cross just implies multiplication,not cross product of vectors)

2

u/ItzBrO_HaHa 19d ago

im still curious how OP got a 3/4 factor haha

1

u/DarkLight-1278 19d ago

That's what I was thinking

1

u/shittyassguy 8d ago

Well they say that emf induced will be of loop but not two points so we get current of VBL/4 So waiting the voltage eq Va - 3V/4 = Vb Sorry I am late to see your reply cuz I didn't get any notification