Question

A set of atoms in an excited state decays ______.

Options

• in general to any of the states with lower energy.

• into a lower state only when excited by an external electric field.

• all together simultaneously into a lower state.

• to emit photons only when they collide.

Answer 1

A set of atoms in an excited state decays in general to any of the states with lower energy.

Explanation:

When a hydrogen atom is excited, it returns to its: normal unexcited (or ground’ state) state by emitting the energy it had absorbed carli¢r, This energy is given out by the atom in the form of radiations of different wavelengths as the electron jumps down from a higher to a lower orbit. The transition from different orbits causes different wavelengths, these constitute spectral. series which ‘are characteristic of the atom emitting them. When observed through a spectroscope, these radiations are imaged as sharp and straight vertical lines of a single colour.

The spectral lines arising from the transition of an electron form a spectra series.

1. Mainly there are five series and each series is named after its discoverer as Lyman series, Balmer series, Paschen series, Bracket series and Pfund series.

2. According to Bohr's theory, the wavelength of the radiations emitted from hydrogen atom is given by

`1/λ = R[1/n_1^2 - 1/n_2^2]`

⇒ λ = `(n_1^2n_2^2)/((n_2^2 - n_1^2)R) = n_1^2/((1 - n_1^2/n_2^2)R)`

where n₂ = outer orbit (electron jumps from this orbit), , = inner orbit (electron fills in this orbit)

A set of atoms in an excited state decays in general to any of the states with lower energy.