Question

example probs I need help with

What is the maximum voltage (emf) created by a 50 loop de generator with a cross-sectional area of 0.5 square meter if the magnetic field changes from 0 to 2 Tin 0.2 seconds? What is the maximum voltage (emf) created by a 100 loop ac generator with a cross-sectional area of 0.1 square meter spinning at 60 Hz in a uniform magnetic field of 0.5 T? A transformer with 200 turns in its primary winding converts the 120 volts from an outlet to 12 volts to operate and electronic device. How many turns must be in its secondary coil? A transformer with 200 turns in its primary winding converts the 120 volts from an outlet to 12 volts to operate and electronic device. If the current in the primary coil is 4 A, what current will be produced in the secondary coil?

Answer 1

Sol:

Here N = 50 A=0.5m^2  
AB= 21
and $\Delta t=0.2s$

Hence induced emf is-

$\varepsilon =N\left ( \frac{A\Delta B}{\Delta t} \right )=50\times \left ( \frac{0.5\times 2}{0.2} \right )=250V$

Here N = 100 A=0.1m^2   and f = 60Hz

B = 0.51

Maximum induced emf is-

$\varepsilon _{max}=2\pi fNBA=2\pi\times60 \times 100\times0.5\times0.1=1885V$

Here N1 = 200 V1 = 120V and V2 = 12 V

Now turn in secondary coil-

$N_{2}=\frac{V_{2}}{V_{1}}\times N_{1}=\frac{12}{120}\times 200=20 turn$

Now I1 =4A then

$I_{2}=\frac{I_{1}V_{1}}{V_{2}}=\frac{4\times 120}{12}=40A$