What is the temperature if the peak of a blackbody spectrum is at 19.0 nm ?

1.52 * 10⁵ K

Explanation:

When the temperature of a blackbody radiator increases, the overall radiated energy increases and the peak of the radiation curve moves to shorter wavelengths. When the maximum is evaluated from the Planck radiation formula, the product of the peak wavelength and the temperature is found to be a constant.  

By Wien's Law,

λ * T = 2.898 * 10⁻³ mK

∴ T = 2.898 * 10⁻³/λ

Given λ = 19 nm = 19 * 10⁻⁹

T = 2.898 * 10⁻³ / 19 * 10⁻⁹

  =1.52 * 10⁵ K

wavelength divides in half and speed stays the same.