Question

Choose the correct statements from the following:
a. Steel is more elastic than rubber.
b. The stretching of a coil spring is determined by the Young’s modulus of the wire of the spring.
c. The frequency of a tuning fork is determined by the shear modulus of the material of the fork.
d. When a material is subjected to a tensile (stretching) stress, the restoring forces are caused by interatomic attraction.

Answer 1

Just try to find the argument behind each statement, for the wrong statement(s) you’ll find some other reasoning to negate those.
a. Steel has more stress for the strain in the rubber.
b. Stretching of a coil spring is by force constant.
c. Frequency of the tuning fork is determined by Young's modulus.
d. Material is subjected to a tensile stress, has restoring forces which is caused by interatomic attraction.

Complete answer:
material is able to stretch under some applied force and is able to get back to its original state when the force is removed. A rubber band is not really more ‘elastic’ rather it's more stretchable. After force removal, it can’t retain back its original shape as much as a steel wire can. So, this statement is correct.

Statement 2: When some force is applied a spring stretches according to the Hooke’s law i.e. $\vec F = k.\vec x$, where $\vec F$ denotes the force applied and $\vec x$ is the displacement or the stretching amount of the spring. Now, k is known as the spring constant for the spring. The spring constant is a constant quantity that depends on properties like thickness of the material, number of turns per unit length, diameter of the coil, overall length etc. but not on the Young’s modulus of the substance. So, this statement is incorrect.

Statement 3: Shear modulus of a material is the ratio of shear stress to the shear strain. But to determine the frequency of a tuning fork no amount of shear stress is needed to provide and shear modulus is not involved in the whole scenario. It’s completely determined by the young’s modulus, density and the dimension of the fork. So, the statement is incorrect.

Statement 4: When any material is subjected to some tensile stress it gets stretched. In molecular level, the interatomic distances between the molecules increases. As the molecules get further separated from their equilibrium just like a stretched spring a restoring attracting force arises within them to oppose the tensile stress. So, the statement is correct.

Hence, the correct answer is option (A) and (D).

Note: Here, the quantities like young’s modulus or shear modulus depends only on the nature of the material, not on any external factors like mass, dimension of the body or externally applied forces. These are known as the intrinsic property of the material.