PAG 5.1 - Determining Wavelength of Light using a Diffraction grating

Question 1

What safety precautions should be taken when operating a laser?

Answer 1

• never look directly at the beam
• ensure no reflective surfaces are in the laser’s vicinity

Question 2

Why should the screen you use to display the interference patterns have a matt finish?

Answer 2

Reduce the likelihood of the laser reflecting back into someone’s eye

Question 3

What is monochromatic light?

Answer 3

single wavelength or frequency

Question 4

What does it mean if two light sources are coherent?

Answer 4

same wavelength and constant phase difference

Question 5

What happens to light as it passes through a slit?

Answer 5

Light diffracts as it passes through a slit, with a maximum diffraction occurring when the slit spacing matches the light’s wavelength

Question 6

What safety precautions should be taken when operating with a laser?

Answer 6

• never look directly in the beam
• ensure no reflective surfaces are in the laser’s vicinity

Question 7

Why do bright fringes form on a screen when light is passed through a diffraction grating?

Answer 7

Light diffracts as it passes through the slits and both waves superpose. Bright fringes are formed by constructive interference

Question 8

Why do dark fringes form on a screen when light is passed through the diffraction grating?

Answer 8

Points where the waves meet in antiphase, destructive interference occurs and dark fringes are formed

Question 9

OPTIONAL:
What equation is used to determine the wavelength of light when using a diffraction grating?

Answer 9

nλ = dsinθ
n - order of diffraction pattern
d - diffraction grating spacing

Question 10

How is the diffracting grating spacing calculated?

Answer 10

Reciprocal of the number of lines per meter

Question 11

How does a diffraction pattern from a double-slit experiment compare to one from a diffraction grating?

Answer 11

As the number of slits increases, the pattern becomes sharper and the brightness of the fringes increases. More rays are reinforcing the pattern

Question 12

Where is 0 order maxima

Answer 12

straight in line with the laser beam

Question 13

Describe the interference pattern produced if white light passed through the diffraction grating?

Answer 13

central white fringe would be produced. All other bright fringes would consists of a spectra of light, with blue closest and red the furthest

Question 14

Why does the interference pattern from white light consist of spectra?

Answer 14

white light is a mix of all other colours and so contain light of many different wavelengths