Basic Electricity 2, WASSCE (SC), 2021

Question 4

 

  1. With the aid of a diagram, explain Fleming’s Left-Hand Rule with respect to motors.
  1. A d.c. shunt generator connected across a 30 V supply has an armature current of 20 A and an armature resistance of 0.7Ω. Calculate the generated voltage

 

Observation

The expected answers were;

  1. Diagram explaining Fleming’s Left-Hand Rule with respect to motors. 

 

Diagram  Description automatically generated

 

                                                                        OR

 

Diagram  Description automatically generatedVT = Va - IAR 

 

 

 

 

 

 


 

When a left hand is held with the thumb, forefinger and middle finger mutually perpendicular, if the forefinger points in the direction of a magnetic field and the middle finger points in the direction of the current flowing through a conductor within the field, then the conductor moves in the direction of the thumb.

 

(b)        Calculation of the generated voltage

 

VT = Va - IAR        

Va= VT + IAR                     

    

VT = Va - IAR 

     = 30 + (20*0.7)

Va = 44V

 

Many of the candidates that attempted this question did fairly well. However, some could not draw the diagram to explain Fleming’s Left Hand-Rule. Very few could not calculate the generated voltage.