A Level Physics Practice Exam

What order of spectrum is observed when the angle of diffraction is 50 degrees?

1. 0th order

2. 1st order

3. 2nd order

4. 3rd order

The correct answer is: 1st order

The answer is the first order of the spectrum, which corresponds to a specific diffraction condition relating to the angle of diffraction. When light passes through a diffraction grating, it is separated into its component wavelengths, forming a series of spectra (or orders) based on the angle at which each wavelength is diffracted. The first-order spectrum is produced when the path difference between light waves diffracted by adjacent slits equals one wavelength of the light. This situation occurs at a specific angle which, in this case, is 50 degrees. The general formula that relates the angle of diffraction (\( \theta \)), the order of the spectrum (\( n \)), and the wavelength of the light (\( \lambda \)) is given by: \( d \sin(\theta) = n \lambda \) where \( d \) is the distance between the slits in the grating. Setting \( n = 1 \) for the first order, when the angle reaches 50 degrees, the condition can be satisfied, indicating that the first-order spectrum is indeed observed at that angle. Whereas the 0th order refers to the direct transmitted light without diffraction, higher orders like the second or third would require angles that result in