measurement of the wavelength of monochromatic light

Question 1

name a source of monochromatic light.

Answer 1

a sodium vapour lamp is a monochromatic light source.

Question 2

if the diffraction grating has 400 lines per mm, what is the distance between each line on the diffraction grating?

Answer 2

distance between each line on the grating= 1/400 mm= 0.0025mm =0.0000025m between each line

Question 3

how was the spectrometer set up(ie errors and precautions)

Answer 3

the spectrometer was set up by
adjusting the eyepiece till the crossthreads are in focus
adjusting the telescope til a distant object is in focus
adjusting the slit until a narrow, bright image of the sodium vapor lamp light can be seen
levelling the turn table, making sure the grating is at right angles to the collimator and parallel to the slit.

Question 4

explain how the order of the images were identified

Answer 4

viewed in a straight line from the collimator is the 0th order image. the first image on either side of this image when viewed through the spectrometer is the right and left first order images.

Question 5

describe how the angles between the first order images was measured.

Answer 5

locate the first order image on the left and place it in the centre of the crossthreads. read the position from the vernier scale. Repeat for the first order image on the right. The difference gives the angle between the first order image

Question 6

what formula did you use to calculate the wavelength of the light?

Answer 6

nx= d sin O
n=order image number
x= wavelength
d= grating constant
O= angle between the order image and the oth order image

Question 7

calculate the maximum number of images that are formed on the screen.

Answer 7

n max= d/x

Question 8

the light source is replaced with a source of white light and a series of spectra are formed on the screen. Explain how the diffraction grating produces a spectrum.

Answer 8

when the angle is different, so is the wavelength, so different colours are formed at different angle from the straight through position.

Question 9

explain why a spectrum is not formed at the central(zero order) image

Answer 9

at the straight through position, all wavelengths are present so a white light is seen

Question 10

what effect would each of the following changes have on the bright images formed:

a. using a monochromatic light source of longer wavelength
b. using a diffraction grating having 200 lines per mm
c. using white light

Answer 10

longer wavelength=angle between images increases=images further apart
larger gaps in diffraction grating=smaller angle between images=images closer together
each image is a spectrum of white light