Question

The force, by which the \(\alpha\)-particles are scattered in the \(\alpha\)-particle scattering experiment of Rutherford, is

• A. Gravitational force
• B. Coulomb's force
• C. Nuclear force
• D. Magnetic force

Hint:

Rutherford's experiment is a cornerstone of modern physics. Remember its key conclusion: the atom consists of a tiny, dense, positively charged nucleus surrounded by a large volume of mostly empty space containing electrons. The scattering is a classic example of an interaction governed by Coulomb's law.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Rutherford's gold foil experiment (or \(\alpha\)-particle scattering experiment) involved bombarding a thin sheet of gold foil with positively charged alpha particles. The scattering pattern of these particles led to the discovery of the atomic nucleus. The question asks for the fundamental force responsible for this scattering.

Step 2: Detailed Explanation:
Let's analyze the forces involved:
\begin{itemize} \item Nature of Particles: The \(\alpha\)-particle is a helium nucleus (\(_{2}^{4}\text{He}^{2+}\)), which is positively charged. The target, the nucleus of a gold atom, is also positively charged (as it contains protons).
\item Coulomb's force: This is the electrostatic force of repulsion between two like charges (positive \(\alpha\)-particle and positive nucleus). This force is long-range and follows an inverse-square law (\(F \propto 1/r^2\)), which perfectly explains why most particles passed straight through (far from a nucleus) while a few were deflected at large angles (passed close to a nucleus).
\item Gravitational force: This is the force of attraction between masses. While it exists, it is extremely weak compared to the electrostatic force at the atomic scale and is completely negligible in this context.
\item Nuclear force: This is a very strong, short-range attractive force that holds protons and neutrons together within the nucleus. It only acts over distances of about \(10^{-15}\) m. The \(\alpha\)-particles are repelled by the Coulomb force long before they get close enough for the nuclear force to be significant, except in very high-energy head-on collisions. The scattering itself is governed by the electrostatic repulsion.
\item Magnetic force: This force acts on moving charges within a magnetic field. There is no external magnetic field applied in this experiment, so this force is not the cause of the scattering.
\end{itemize} The primary interaction causing the \(\alpha\)-particles to deviate from their straight paths is the electrostatic repulsion between the positively charged \(\alpha\)-particles and the positively charged gold nuclei. This force is known as Coulomb's force.

Step 3: Final Answer:
The force responsible for the scattering is Coulomb's force. Therefore, option (B) is correct.