• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Estimating the wavelength of light using a double-slit and a plane diffraction grating

Extracts from this document...



Estimating the wavelength of light using a double-slit and a plane diffraction grating        


To project a Young’s interference pattern on a screen and make measurements to estimate the wavelength of light

To estimate the wavelengths of the different colours of the spectrum produced using a fine diffraction grating




1 double slit

Mounted on a large cardboard

1 translucent screen

Ground glass

1 Compact light source

With vertical filament

1 Low voltage power supply


1 Magnifying glass


2 metre rule

100 cm

1 vernier caliper

Smallest division 0.1mm

1 diffraction grating

3000 lines per cm

1 ray-box

Without lens and slit plate


Using a double-slit

In the Young’s double slit experiment, two rays through the slits interfere to give the interference pattern. Bright fringes occur at positions where constructive interference occurs (Fig.1). The path difference from the slits at an angle θ is a multiple n of the wavelength λ, i.e.

a sin θ=nλ,

where n=1,2,3… is known as order number.

For small value of θ,

Sinθ= tanθ= s/D

Where s is

...read more.


  1. A ‘T’ with 2 metre rules was formed

and it was pointed towards

a ray-box 1 to 2 metres away (Fig 4).

  1. A diffraction grating was held against one end of a metre rule. The vertical filament of the ray-box lamp was viewed through the grating. A diffraction pattern consisting of the first and second order spectra would be seen.(Fig 5)
  1. A pencil was moved along the second metre rule until it was in line with the middle of the blue colour of the first order spectrum. The distance x was measured.
  1. From x, tanθ and then sinθ were found. The grating formula λ=dsinθ was applied to calculate the wavelength of the light.
  1. Steps 9 and 10 were repeated with the green and red colours in turn and the wavelength of the different colours were calculated.

Results and discussion

Using a double-slit

  1. Calculate the wavelength of light using the formula λ=ay/D.

Slit separation a = 0.3 mm

Fringe separation y/mm

(4 fringes measured)




Slit-to screen distance D/m




Wavelength λ=ay/D




...read more.


-There are errors from fringe separation reading using vernier caliper.

 Maximum error = 0.1/2=0.05mm

 For example, the first reading of y is actually 0.85+0.1mm

 So the wavelength obtained is not accurate.

For the diffraction grating experiment,

-It is difficult to locate the exact fringe for that particular colour.

-There are errors from readings of x using a metre rule.

 Maximum error = 0.1/2=0.05cm

 Reading of x for 1st order green fringe is actually 0.17+0.001m

 So the wavelength obtained is not accurate.

  1. In this experiment, the first order spectrum is used foe measuring he wavelengths of different colors. Give one advantage and disadvantage of using the second order spectrum instead.

The advantage is that the angular separation of second order is larger than that of first order. It will have a smaller measurement percentage error.

The disadvantage is that the intensity of the second order is lower and the corresponding fringes for each colour are difficult to locate.

   Safety precaution

-The light source is very hot. Hold it with care.


Tao, Lee & Mak’s A-Level Practical Physics Third Edition (Oxford).P.72-75

...read more.

This student written piece of work is one of many that can be found in our AS and A Level Waves & Cosmology section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Waves & Cosmology essays

  1. Peer reviewed

    Black Holes Research and Report

    4 star(s)

    entering them emits x-rays, proving them to be one or the other. Micro black hole - also known as quantum mechanical black holes, they are tiny hypothetical black holes which have not yet been discovered, but are a very possible occurence.

  2. Peer reviewed

    What affects the voltage output of a solar panel?

    3 star(s)

    Observing and Recording Results Background 1 Test 1 Background 2 Test 2 Background 3 Test 3 Average 10 0.05 1.93 0.05 1.94 0.05 1.92 1.88 50 0.07 0.95 0.07 0.94 0.06 0.95 0.88 100 0.07 0.48 0.07 0.48 0.07 0.49 0.413333 The trial run was very successful and when a

  1. Investigate any relationship present between the distance between a solar cell and a lamp, ...

    Evaluation: I feel that the experiment was a success, as I do not seem to have encountered any anomalies whilst doing my experiment. The values weren't all precisely on the line, but it is rare for an experiment to go exactly correct, with slight errors being made, slightly off equipment, or faults of rounding.

  2. The aim of my coursework is to calculate the wavelength of red laser light ...

    The grating causes the concentrated light to break up again. There is maxima on the screen where light is in phase. The fringe in the middle is called the central maximum or 0th order spectrum. The next fringes, left and right from the central maximum is called 1st order spectrum,

  1. Refractive index by tracing light rays

    My line of sight moved towards D. The line was noticed to disappear suddenly from view at a certain point. 4. Two pins were placed to mark the direction beyond which the dark line just could not be seen. 5.

  2. Diffraction Grating with White Light Source

    Procedures 1. Use the ray box with vertical filament. Place the lamp about 2 m away. 2. Place two meter rules at right angles to each other as shown. Set the diffraction grating vertically at one end of the meter rule. Observe the horizontal diffraction pattern (color spectrum) of the filament by viewing through the diffraction grating.

  1. Waves and Cosmology - AQA GCE Physics Revision Notes

    * Another experiment is using a cube with 4 different sides (matt black, matt white, smooth black and shiny silver surfaces). If it is heated with a light bulb inside it, as voltage is adjusted, the temperature of bulb would vary.

  2. I intend to investigate whether any correlation exists between the wavelength of light exerted ...

    This reduces the data output of the microcontroller by roughly a tenth, and so the actual number of measurements that will be sent will be (in a best-case scenario 1200: 115200/96=1200 To avoid saturating the connection, I recalculated the delay time by dividing 1 second by 1200 measurements 1/1200=8.3x10-4 seconds I then implemented this in the program code.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work