Physics Class 11 Chapter 9. Mechanical Properties of Solids | Page 9

where, η = modulus of rigidity of the material of cylinder, r = radius of cylinder,
and 1 = length of cylinder, Work done in twisting the cylinder through an angle θ W = 1 / 2 Cθ 2
Relation between angle of twist( θ) and angle of shear( φ) rθ = lφ or φ = r / l = θ