NCERT Class 9 Science — Chapter 4: Structure of the atom

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According to electromagnetic theory, what is the primary consequence of an electron undergoing acceleration in a circular orbit, which became a drawback for Rutherford's model?

Official previous-year question

Verified 1 Aug 2026.

Options

AThe electron would move in a straight line.
BThe nucleus would expand due to repulsion.
CThe electron would gain mass.
DThe electron would radiate energy and lose stability.

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Solution

Correct Option

The correct option is

The electron would radiate energy and lose stability.

Explanation

Rutherford’s atomic model likened the atom to a solar system, where electrons revolve around a positively charged nucleus in circular orbits. However, this model faced a significant challenge when analyzed through the lens of classical electromagnetic theory proposed by James Clerk Maxwell.

Analysis

Acceleration of Charged Particles: According to electromagnetic theory, charged particles undergoing acceleration emit electromagnetic radiation continuously.
Circular Motion and Acceleration: An electron moving in a circular orbit is constantly changing its direction of motion. Therefore, even if its speed remains constant, it is subject to centripetal acceleration.
Energy Loss and Instability: Since the electron is an accelerated charged particle, it must radiate energy. As it loses energy, the radius of its orbit would gradually decrease.
Consequence: The electron would follow a spiral path and eventually collapse into the nucleus. Calculations suggest this collapse would occur in a fraction of a second (approximately \(10^{-8}\) seconds), rendering the atom unstable. Since atoms are known to be stable, this was a major drawback of Rutherford's model.

Key Takeaway: Rutherford’s model failed to explain the stability of the atom because classical electromagnetic theory predicts that an accelerating electron in a circular orbit will lose energy and spiral into the nucleus.

Your note

More from Chapter 4: Structure of the atom

Which sub-atomic particle was identified by J. Chadwick in 1932?

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With reference to Neils Bohr’s model of the atom, consider the following statements: 1. Only certain special orbits known as discrete orbits of electrons are allowed inside the atom. 2. Electrons radiate energy continuously while revolving in discrete orbits. 3. These discrete orbits are called energy levels. Which of the statements given above is/are correct?

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Consider the following statements regarding the discovery and properties of neutrons: 1. They were discovered by J.J. Thomson in 1897. 2. They are present in the nucleus of all atoms including hydrogen. 3. A neutron has no charge and a mass nearly equal to that of a proton. Which of the statements given above is/are correct?

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With reference to 'Valency', consider the following statements: 1. It is the combining capacity of the atoms of elements. 2. Atoms react to achieve a duplet in the outermost shell in all cases. 3. If the outermost shell has 8 electrons, the valency is 8. Which of the statements given above is/are correct?

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With reference to the definition of an element, consider the following statements: 1. Elements are defined by the number of protons they possess. 2. Atoms of a given element can have different numbers of protons. 3. The atomic number is characteristic of a particular element.

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Correct Option

The correct option is

The electron would radiate energy and lose stability.

Explanation

Analysis

Acceleration of Charged Particles: According to electromagnetic theory, charged particles undergoing acceleration emit electromagnetic radiation continuously.
Circular Motion and Acceleration: An electron moving in a circular orbit is constantly changing its direction of motion. Therefore, even if its speed remains constant, it is subject to centripetal acceleration.
Energy Loss and Instability: Since the electron is an accelerated charged particle, it must radiate energy. As it loses energy, the radius of its orbit would gradually decrease.
Consequence: The electron would follow a spiral path and eventually collapse into the nucleus. Calculations suggest this collapse would occur in a fraction of a second (approximately \(10^{-8}\) seconds), rendering the atom unstable. Since atoms are known to be stable, this was a major drawback of Rutherford's model.