# A scientist is investigating the emission spectra of two different gases. Gas X produces a spectrum with lines in the visible and ultraviolet regions. Gas Y produces a spectrum with lines only in the infrared and visible regions. Explain how line emission spectra are produced and why the photons emitted by Gas X include higher energy photons than those emitted by Gas Y.

> Eduqas A-Level Physics — 2.7 Photons · Explain · 5 marks

> When electrons in excited atoms fall back to lower energy levels, they release energy as photons. Each element produces a unique pattern of spectral lines.

## Mark scheme (5 marks)

1. Electrons in atoms exist at specific/discrete energy levels
2. When an electron absorbs energy it moves to a higher energy level (becomes excited)
3. When the electron falls back to a lower energy level it releases a photon
4. The energy of the photon equals the difference in energy between the two levels
5. Gas X emits higher energy photons because its electrons fall between energy levels with a larger energy difference / ultraviolet photons have higher frequency so higher energy than infrared photons

## Key terms

- [photon](https://www.gradenine.co.uk/glossary/photon)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-scientist-is-investigating-the-emission-5b1b725d) · Published by Druglandscape Ltd.