Express the frequency in inverse seconds. n=4--> n=3. can you tell me what formulas to use, because i have like 6 more of these to do and i can't figure it out.

Explanation:

When an electron jumps from one energy level to a lower energy level some energy is released in the form of a photon.

The difference in energy between the two levels is the energy of the photon and that energy is related to the frequency of the photon by the Einstein - Planck equation:

Where,

So, to find the frequency you must first find the energy.

The transition energy can be calculated using the formula:

Where E₀ = 13.6 eV ( 1 eV = 1.602×10⁻¹⁹ Joules) and n = 1,2,3,...

So, the transition energy between n = 4 and n = 3 will be:

Now you can use the Einstein - Planck equation: