Which of the following has the least count of 0.001 cm? MCQ with Answer and Explanation

Explanation:
The acceleration due to gravity is given by g = GM/R². For a small change, taking the derivative or using error approximation: Δg/g = -2(ΔR/R). If R shrinks by 1% (ΔR/R = -1%), then Δg/g = -2(-1%) = +2%. Therefore, the value of 'g' will increase by approximately 2%.

Explanation:
Resistance (R) of a wire is given by R = ρL/A, where ρ is resistivity, L is length, and A is cross-sectional area. If L becomes 2L and A becomes 2A, the new resistance is R' = ρ(2L)/(2A). The 2s cancel out, leaving R' = ρL/A = R. Thus, the resistance remains entirely unchanged.

Explanation:
Steel has high retentivity, retains magnetism, used for permanent magnets. Soft iron has low retentivity, used for electromagnet core (temporary). Alnico, ferrites also used.