Question

The working principle of spring balance is :

• A. Newton's law of motion
• B. Hooke's law
• C. Ohm's law
• D. None of the above

Answer 1

The correct option is B

Hooke's law

Explanation for correct option:

By exerting an external force on the spring, it can be either compressed or expanded. Spring will provide an opposing balancing force when an external force is applied, keeping the spring in a stable state. The spring will give the same balancing force for the same extension and compression distances.

Suppose to extend the spring at $x$ distance and the external force applied is $F_{ext}$. The spring will produce an opposite balancing force to keep the spring stable is $F_{bal}$

$$\begin{gathered} F_{bal}\propto x \\ \Rightarrow F_{bal}=kx \end{gathered}$$

Where $k$ is the spring constant

A balanced condition

$$\begin{gathered} F_{ext}=F_{bal} \\ {F}_{ext}=kx......\left(i\right) \end{gathered}$$

The last equation is called Hooke's equation. For various, the distance applied force should be varied too.

Explanation for incorrect option(s):

A: Newton's law of motion

1. Newton’s $1$st law states that a body at rest or uniform motion will continue to be at rest or uniform motion until and unless a net external force acts on it.
2. Newton $2$nd law of motion states that the rate of change of momentum is directly proportional to the applied force.
3. Every action has an equal and opposite reaction.

C: Ohm's law

Ohm's law states that the voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions and temperatures remain constant. In the equation, the constant of proportionality, $R$, is called resistance and has units of ohms, with the symbol $\Omega$.

Hence, option B is correct.