This is a Problem 7.7 fom Griffiths Introduction to Electrodynamics (3ed)
A metal bar of mass m slides frictionlessly on two parallel conducting rails a
distance l apart. A resistor R is connected across the rails and a uniform magnetic field B, pointing into page, fills the entire region.
If the bar moves to the right at speed v, what is the current in the resistor ?
The Attempt at a Solution
my reasonig is:
magnetic flux is:
A0 is initial surface, and A1 is surface which bar makes moving to the right with spead v.
A1=x*l=v*t*l , but v is also function of t, so: A1=v(t)*t*l
I know that equation for A1 is wrong, becouse when I try to get electromotive froce
I get this:
in solution manual it's:
Can someone explain why my reasoning is wrong, it seams logical to me.