Pick up the incorrect statement from the following: The torsional resistance of a shaft is directly proportional to A. Modulus of rigidity B. Angle of twist C. Reciprocal of the length of the shaft D. Moment of inertia of the shaft section

The correct answer is C. Reciprocal of the length of the shaft.

The torsional resistance of a shaft is the ability of a shaft to resist the twisting force applied to it. It is directly proportional to the following:

• Modulus of rigidity: The modulus of rigidity is a measure of the stiffness of a material. It is the ratio of shear stress to shear strain.
• Angle of twist: The angle of twist is the angle through which the shaft twists when a torque is applied to it.
• Moment of inertia of the shaft section: The moment of inertia is a measure of the resistance of a shape to bending. It is calculated by multiplying the area of the cross-section of the shaft by the square of the radius of gyration.

The length of the shaft does not affect the torsional resistance of the shaft. This is because the torque applied to the shaft is transmitted through the entire length of the shaft, and the length of the shaft does not affect the amount of shear stress that is developed in the shaft.

Therefore, the incorrect statement is C. Reciprocal of the length of the shaft.