Find the magnitude of the magnetic flux through buttom of the open-topped rectan

Through long side or short side, there is no magnetic fieldpassing. This is because the sides are parallel to the direction ofthe magnetic field lines. So, 0 Wb pass through either logn sideand either short side.
 
For, bottom side:
Area of bottom side = L * W = 27.5 * 12 = 330 cm2 =0.033 m2
So, Amount of flux through bottom side = 0.03 * 0.033 =0.00099 Wb

Magneticflux   φ   =   B.A   =   B* A * cos θ
 
   Here bold letters arevectors. θ is angle between direction of magnetic field andarea vector which is normal to surface of vector.
 
   1.   Alonglongside      θ   =   900
 
            φlong   =   B* A * cos900    =   0
 
   2.   Along shortside      θ   =   900
 
            φshort   =   B* A * cos900    =   0
 
   3.   Throughbottom   θ   =   00
 
         φbottom   =   B* A * cos00    =   0.0300 *A
 
         φbottom   =   0.0300* ( 27.5 * 10-2 * 12 * 10-2)
 
         φbottom   =   9.9* 10-4   Wb