RP 2 interference by a diffraction grating

Question 1

what is the main aim of this practical?

Answer 1

• calculate the wavelength of laser light using diffraction grating

Question 2

what are the variables in this experiment?

Answer 2

independent variable - distance between maxima

dependent variable - angle betwen normal and each order

control vairable - wavelength, slit seperation and distance between slits and screen

Question 3

what is the general method for this practical?

Answer 3

• place laster on retort stand and DG infront of it
• use set square to ensure beam passes so it meets screen perpendicularly
• set D to 1m using metre ruler
• darken room and turn on laser
• identify zero order maximum
• measure d to orderwith vernier calliper and take average
• repeat with diffraction grating with diff number of slits per mm

Question 4

what do we calculate from our results?

Answer 4

nL = d sinØ

d = 1 / N

arctan ( hn / D ) forø

calc mean Ø for each value

comapre with accepted value

Question 5

how do we avoid parallax error in measurement of fringe width!

Answer 5

• use set square

Question 6

how can we lower percentage uncertainty?

Answer 6

• use grating with more lines per mm

Question 7

how can we reduce uncertainty in measurements?

Answer 7

tend to take multiple readings find mean, and also divide by whole record

Question 8

what are some safety precuatios?

Answer 8

• do not point lasers at eye
• remove reflecticve surfaces from room to ensure no laser light is reflected into anyones eyes