A dc series motor is coupled to a load whose torque is proportional to speed. It is fed by a single phase ac supply through a full converter. When speed is 500 rpm, firing angle is 45°. It is desired to raise the speed. It will be necessary to

• A. decrease the firing angle
• B. increase the firing angle
• C. either decrease or increase the firing angle depending on the required speed
• D. decrease the load torque