An electron drops from the -1.5 eV level to the -3.4 eV level. What is the emitted photon's energy?

• 1.9 eV
• 4.9 eV
• 1.5 eV
• 3.4 eV

An electron drops from the -1.5 eV level to the -3.4 eV level. What is the emitted photon's energy?

• 1.9 eV
• 4.9 eV
• 1.5 eV

White light shines through cool hydrogen gas. What appears in the spectrum?

• Bright lines on a dark background
• Dark lines where the gas swallowed photons
• A smooth rainbow with no lines

The levels are negative because the electron is trapped, and 0 eV means it just escapes.

Circle one:   True   False

A hydrogen electron at -13.6 eV absorbs a 10.2 eV photon. Which level does it reach?

• -3.4 eV
• -1.5 eV
• -10.2 eV
• 0 eV

How do the dark absorption lines of a gas compare with its bright emission lines?

• They sit at the same frequencies
• They sit halfway between the bright lines
• They use entirely different colours

An electron falls from the -0.9 eV level to the -3.4 eV level. What is the photon energy in eV?

Answer: ______________

An electron falls from the -0.9 eV level to the -3.4 eV level. What is the photon energy in eV?

Answer: ______________

Tom works out the -1.5 eV to -3.4 eV jump as -3.4 minus -1.5 = -1.9 eV and claims the photon carries negative energy. What is his mistake?

• He subtracted the wrong way round
• He picked energy levels from two elements
• He used the wrong units for light

Starlight shows dark lines at exactly the frequencies hydrogen emits when hot. What does that tell you?

• Hot hydrogen inside the star makes the lines
• Cool hydrogen between the star and us swallowed those photons
• Dust blocks every colour by the same amount