A conducting wire is stretched by applying a deforming force, so that its diameter decreases to 40% of the original value. The percentage change in its resistance will be:
A metal plate of area 10-2m2 rests on a layer of castor oil, 2 × 10-3m thick, whose viscosity coefficient is 1.55 Ns/m2. The approximate horizontal force required to move the plate with a uniform speed of 3 × 10-2ms-1 is: