Atomic line spectra and energy levelsEdexcel International A Level Physics: Flashcards

Exam questions on Atomic line spectra and energy levels

1. A gas discharge tube containing hydrogen at low pressure emits light when a high voltage is applied across it. When the light is viewed through a diffraction grating, a small number of separate coloured lines is seen against a dark background.
   Explain why dark lines appear in an absorption spectrum at the same frequencies as the bright lines in the emission spectrum of the same gas.2 marks
2. The lowest three energy levels of a hydrogen atom are n = 1 at −13.6 eV, n = 2 at −3.40 eV and n = 3 at −1.51 eV. Use the Planck constant h = 6.63 × 10⁻³⁴ J s and 1 eV = 1.60 × 10⁻¹⁹ J.
   Calculate the frequency of the photon emitted when an electron moves from n = 2 to n = 1.2 marks
3. An atom of an element has energy levels of −5.4 eV (the ground state), −3.1 eV and −1.5 eV. A sample of the element is excited so that some of its atoms are in the −1.5 eV level. Use the Planck constant h = 6.63 × 10⁻³⁴ J s and 1 eV = 1.60 × 10⁻¹⁹ J.
   Calculate the frequency of the photon emitted when an atom moves from the −1.5 eV level to the ground state.3 marks