Here's how to determine the color of peak wavelength for an F-type star with a photosphere temperature of 7240 K:

1. Wien's Displacement Law:

Wien's Displacement Law relates the peak wavelength of blackbody radiation to its temperature:

* λ_max * T = b

Where:

* λ_max is the peak wavelength in meters

* T is the temperature in Kelvin

* b is Wien's displacement constant (approximately 2.898 x 10^-3 m·K)

2. Calculate Peak Wavelength:

* Rearrange the equation to solve for λ_max:

* λ_max = b / T

* Substitute the values:

* λ_max = (2.898 x 10^-3 m·K) / 7240 K

* λ_max ≈ 4.00 x 10^-7 meters

3. Convert to Nanometers:

* Since wavelengths are often expressed in nanometers (nm), convert the result:

* λ_max ≈ 400 nm

4. Determine Color:

* 400 nm falls within the violet range of the visible spectrum.

Important Note: While the peak wavelength is in the violet range, F-type stars appear white-blue to the human eye. This is because their light output spans a broader range of wavelengths, with a significant contribution from the blue part of the spectrum.