Final answer:
Dynamic braking of the motor's shaft is NOT used as a method for the speed control of a universal motor.
Step-by-step explanation:
The universal motor is designed to operate on either AC or DC power and is widely used in portable power tools and domestic appliances. One of the methods that is NOT used for the speed control of a universal motor is dynamic braking of the motor's shaft (C). Let's break down the methods:
Tapped field windings with a switch selector (A) allow for changes in the field strength, which alters the speed.
Varying the voltage using semiconductor devices (B) is a common method of speed control in universal motors, where adjusting the supply voltage changes the speed.
Using an adjustable centrifugal switch in parallel with a resistor (D) can indeed modify a motor's speed, as altering the point at which the centrifugal switch operates can change motor characteristics.
Thus, it's D, the use of a centrifugal switch with a resistor for speed control, that is not typical for universal motors. Dynamic braking is generally used to quickly stop a motor rather than control its operational speed.