Determine Wavelength Using Diffraction Grating

Question 1

Describe the method

Answer 1

• Shine a laser through the diffraction grating onto screen
• measure distance between central fringe and 1st order maxima (next bright fringe) using ruler
• measure distance from grating to screen using ruler
• use protractor to fine angle from central maximum
Or
Use tan = distance between central fringe and one next to it / distance between grating and screen
• angle = inverse tan
• Don’t shine light in eyes

Question 2

Calculations

Answer 2

• Use protractor to find angle from central maximum
• Use tan = distance between central fringe and one next to it / distance between grating and screen
• angle = inverse tan
• d sin = n 𝜆
• To find d
Read how many lines per mm on the packaging
Calculate slit spacing
• Measured first order, n=1

Question 3

Analysis

Answer 3

• Graph
d sin against n
gradient = 𝜆

Question 4

Accuracy

Answer 4

• use diffraction grating with smaller d, maxima more spaced out

• measure distance between corresponding maxima and halve

• use larger room for larger distances to reduce uncertainty