Energy levels and line spectraAQA A-Level Physics: Mind map

Exam questions on Energy levels and line spectra

1. A neon sign glows when a current passes through low-pressure neon gas. When its light is viewed through a diffraction grating, a few bright coloured lines are seen against a dark background instead of a continuous band of colours.
   Explain why the spectrum is made of separate lines and not a continuous band.2 marks
2. Some of the energy levels of a hydrogen atom are: n = 1 at −2.18 × 10⁻¹⁸ J, n = 2 at −5.45 × 10⁻¹⁹ J and n = 3 at −2.42 × 10⁻¹⁹ J.
   A photon of energy 1.0 × 10⁻¹⁸ J passes through hydrogen gas with all the atoms in the ground state, and is not absorbed. Explain why.2 marks
3. Astronomers study the light from a cloud of hydrogen gas. Some of the energy levels of a hydrogen atom are: n = 1 at −13.6 eV, n = 2 at −3.40 eV, n = 3 at −1.51 eV and n = 4 at −0.85 eV.
   Calculate the wavelength of the photon emitted when an electron falls from n = 3 to n = 2.3 marks