It is desired to measure the magnitude of field between the poles of a powerful loud speaker magnet. A small flat search coil of area `2 "cm"^2` with 25 closely wound turns, is positioned normal to the field direction, and then quickly snatched out of the field region. Equivalently, one can give it a quick `90^@` turn to bring its plane parallel to the field direction). The total charge flown in the coil (measured by a ballistic galvanometer connected to coil) is 7.5 mC. The combined resistance of the coil and the galvanometer is 0.50 `Omega`. Estimate the field strength of magnet.

Explanation

`Q = int_(t_i)^(t_f) I dt`
`=1/R int_(t_i)^(t_f) epsi dt`
`= - N/R int_(Phi_i)^(Phi_f) d Phi`
`= N/R (Phi_i - Phi_f)`
for N= 25 , R=0.50 `Omega, Q = 7.5 xx 10^(-3)` C
`Phi_f = 0 , A = 2.0 xx 10^(-4) m^2, Phi_i = 1.5xx10^(-4) Wb`
`B= Phi_f//A = 0.75 T`