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 `2cm^(2)` with 2

Question

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 `2cm^(2)` with 2

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 `2cm^(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 directio). 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 `0.50Omega` Estimate the field strength of magnet.

Monjur Alahi

4 views

2025-01-04 04:42

1 Answers

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Salim Ahmed Kawsar · Accepted Answer · 2023-02-05T15:29:48+06:00

Area of coil `A=2cm^(2)=2 xx 10^(-4)m^(2)`, Number of turns N=25
Total charge in the coil `theta=7.5 mC (1mC=10^(-3) C)` Resistance of coil `R=0.5Omega`
When the coil is removed from the field, the flux is zero `phi_(r)=0`. Induced current in the coil `I=(e)/(R)=(-N(dphi//dt))/(R) (therefore e=-N (dphi)/(dt)) Rightarrow Idt= (-N)/(R).dphi`
Charge in the coil `Q=intIdt=underset(phi_(0))overset(phi_(f))int-(N)/(R).dphi`
`Q=(-N)/(R) (phi_(f)-phi_(i))Rightarrow Q=(N)/(R) (phi_(i)-phi_(f)) Rightarrow Q=N/R (phi_(0)-0) (phi_(f)=0)`
`Q=(N)/(R) phi_(i) (therefore phi_(i)=BA)`
`Q=N/R` (BA), Magnetic field in the coil B `=(QR)/(NA)=(7.5xx10^(-3)xx0.5)/(25xx2xx10^(-4))=0.75T`
Thus, the strength of magnetic field is 0.75 T.