# Energy levels and Photon emission

Discrete energy levels

• Electrons in atoms only exist in discrete energy levels, each level has a number with n=1 being the ground state.
• Electrons can move down a level by emitting a photon.
• Becasue the energy levels are so defined, when a photon is emitted, the energy can only be o a very certain value.
• The energies involved are so small that you don't use joules as it is not an appropriate unit. Instead we use electron volts.
• The electron volt (eV) is defined as- The kinetic energy carried by an electron after it has been accellerated through a potential difference of 1 volt.
• 1 eV = 1.6 x 10^-19 J
• The energy carried by each photon is equal to the difference in energies between the two levels.
• ΔE = E2-E1 = hf = hc/λ

Fluorescent tubes

• In fluorescent tubes, there is a high voltage applied across mercury vapour.
• The electrons in the mercury atoms are bombarded with high energy electrons (caused by high voltage). As a result, the electrons in the mercury…

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# Energy levels and Photon emission

Discrete energy levels

• Electrons in atoms only exist in discrete energy levels, each level has a number with n=1 being the ground state.
• Electrons can move down a level by emitting a photon.
• Becasue the energy levels are so defined, when a photon is emitted, the energy can only be o a very certain value.
• The energies involved are so small that you don't use joules as it is not an appropriate unit. Instead we use electron volts.
• The electron volt (eV) is defined as- The kinetic energy carried by an electron after it has been accellerated through a potential difference of 1 volt.
• 1 eV = 1.6 x 10^-19 J
• The energy carried by each photon is equal to the difference in energies between the two levels.
• ΔE = E2-E1 = hf = hc/λ

Fluorescent tubes

• In fluorescent tubes, there is a high voltage applied across mercury vapour.
• The electrons in the mercury atoms are bombarded with high energy electrons (caused by high voltage). As a result, the electrons in the mercury…