91影视

1. The side of a square loop is$l=20\mathrm{cm}=20脳{10}^{-2}\mathrm{m}$
2. The resistance of a wire is$R=20\mathrm{尘惟}=20脳{10}^{-3}\mathrm{惟}$
3. The uniform magnetic field is$B=2.0\mathrm{T}$
4. The time for the reducing area to zero is $鈭�t=0.20\mathrm{s}$

The average induced emf can be calculated using the equation of emf relating to change in flux over change in time. To find the average current induced we need to use the equation of Ohm鈥檚 law.

Formulae:

$$\begin{gathered} {蔚}_{avg}=\left|-\frac{d{鈭�}_B}{dt}\right| \\ 鈭�{鈭�}_B=BA \\ {蔚}_{avg}=i_{avg}R \end{gathered}$$

The average emf:

The area of the square loop is

$$\begin{gathered} A=l^2 \\ A={\left(20脳{10}^{-2}\mathrm{m}\right)}^2 \\ A=400脳{10}^{-4}{\mathrm{m}}^2 \end{gathered}$$

The expression of magnetic flux is

$$\begin{gathered} 鈭�{鈭�}_B=BA \\ 鈭�{鈭�}_B=2.0T脳400脳{10}^{-4}{m}^2 \end{gathered}$$

The average induced emf is

$$\begin{gathered} {蔚}_{avg}=\left|-\frac{d{鈭�}_B}{dt}\right| \\ {蔚}_{avg}=\left|-\frac{d{鈭�}_B}{dt}\right| \\ {蔚}_{avg}=\frac{2.0T脳400脳{10}^{-4}{\mathrm{m}}^2}{0.20\mathrm{s}} \\ {蔚}_{avg}=0.40\mathrm{V} \end{gathered}$$

The average current induced in the loop during $鈭�t$:

According to the Ohm鈥檚 law, the average induced current is

$$\begin{gathered} i_{avg}=\frac{{蔚}_{avg}}{R} \\ {i}_{avg}=\frac{0.40V}{20脳{10}^{-3}惟} \\ {i}_{avg}=20A \end{gathered}$$