4.
`e_c=-\frac{ΔФ}{Δt}=-\frac{NScosalpha(B_2-B_1)}{Δt}=-\frac{10.20.10^-4.cos60^o .(0-2.10^-4)}{0,01}=2.10^-4` $(V)$
5.
`S=pi.r^2=pi.0,1^2=0,01pi` $(m^2)$
`alpha=90^o-60^o=30^o`
Lúc đầu: `Ф_1=NBScosalpha=50.0,05.0,01pi.cos30^o=0,068` $(Wb)$
a. `Ф_2=2Ф_1` `\to e_c=-\frac{Ф_2-Ф_1}{Δt}=-\frac{2.0,068-0,068}{0,05}=-1,36` $(V)$
b. `Ф_2=0` `\to e_c=-\frac{Ф_2-Ф_1}{Δt}=-\frac{0-0,068}{0,05}=1,36` $(V)$
6.
Lúc đầu $\overrightarrow{n}\perp\overrightarrow{B} $ `\to Ф_1=0`
Lúc sau $\overrightarrow{n}//\overrightarrow{B} $ `\to Ф_2=BScosalpha=0,01.200.10^-4.cos0^o=2.10^-4` $(Wb)$
`e_c=-\frac{Ф_2-Ф_1}{Δt}=-\frac{2.10^-4-0}{0,04}=-5.10^-3` $(V)$
