Introduction:
The common type of servo motor differs from a normal induction motor in terms of rotor resistance. The correct answer is option 'B', which states that the servo motor has a higher rotor resistance compared to an induction motor.

Explanation:
1. Servo Motor:
- A servo motor is a specific type of motor that is designed for precise control of angular or linear position, velocity, and acceleration.
- It is commonly used in applications where accurate and precise control is required, such as robotics, CNC machines, automation systems, and other motion control applications.
- Servo motors are generally small in size and provide high torque for their size.

2. Induction Motor:
- An induction motor is a commonly used motor in various industrial and commercial applications.
- It operates based on the principle of electromagnetic induction, where a rotating magnetic field is induced in the stator windings, which interacts with the rotor to produce torque.
- Induction motors are known for their simplicity, robustness, and cost-effectiveness.
- They are widely used in applications where high starting torque is not required.

3. Difference in Rotor Resistance:
- The rotor resistance is an important parameter that affects the performance of an electric motor.
- In the case of a servo motor, a higher rotor resistance is preferred as it allows for better control of the motor's speed and position.
- The higher resistance helps in achieving a higher level of precision and accuracy in the motor's operation.
- The increased resistance also improves the motor's ability to hold its position without drifting or oscillating.
- On the other hand, an induction motor typically has a lower rotor resistance to ensure efficient operation and high starting torque.
- The lower resistance allows for the maximum power transfer from the stator to the rotor, resulting in high torque production.

Conclusion:
In conclusion, the common type of servo motor differs from a normal induction motor in terms of rotor resistance. The servo motor has a higher rotor resistance, which enables precise control of position, velocity, and acceleration. On the other hand, an induction motor typically has a lower rotor resistance to ensure efficient operation and high starting torque.