Field lines become straight and perpendicular because every point of circular loop the concentric circles become larger and larger as we move away from the wire.
To solve this problem, we will start by defining each of the variables given and proceed to find the modulus of elasticity of the object. We will calculate the deformation per unit of elastic volume and finally we will calculate the net energy of the system. Let's start defining the variables
Yield Strength of the metal specimen

Yield Strain of the Specimen

Diameter of the test-specimen

Gage length of the Specimen

Modulus of elasticity



Strain energy per unit volume at the elastic limit is



Considering that the net strain energy of the sample is




Therefore the net strain energy of the sample is 
Answer: D) a stone lies on the ground
Explanation:
Potential energy this is defined as the mechanical energy, energy stored, or energy created by the position of an object. Example; energy possessed by a ball while hanging at the top of a steep hill when about to roll down is called a potential energy. This is same as a stone which lies in a floor.