Question

A student designed a transformer to provide current to an electric bell marked 24W,6V from mains supply of 240V. He wound coils 50 turns and N turns on an iron ring. When he connected the coil of 50 turns to the bell and N turns to the a.c source he found out that the transformer was only 60% efficient. Find;

1. The value of N   
2. The power in the primary coil.   
3. State two ways in which the efficiency of the transformer can be increased.     
4. State and explain two factors that determine the magnitude of induced emf in a coil rotating in a magnetic field.

Answer 1

1. ⁵⁰/_N =⁶/₂₄₀
      6N=12000
       N=2000turns
2. 60% → 24W
   100%   =(¹⁰⁰/₆₀ × 24) = 40W
3.  
   1. Using a core of soft magnetic material
   2. Winding primary and secondary coil on the same soft iron core
   3. using thick copper wires to make the coil with current
   4. Laminated core
4.  
   1. Speed of rotation of the coil
   2. The current in the coil
   3. Strength of the magnet
   4. Angle at which coil is cutting the magnetic field.