• 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...

Introduction

Title

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

Objective

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

Apparatus        

Instrument

Descriptions

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

Theory

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.

Middle

  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)

3.4/4=0.85

4.18/4=1.045

5.5/4=1.375

Slit-to screen distance D/m

0.46

0.6

0.7

Wavelength λ=ay/D

554x10-9

523x10-9

589x10-9

...read more.

Conclusion

-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.

Reference

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

    What affects the voltage output of a solar panel?

    3 star(s)

    90 0.09 0.08 0.09 0.09 0.000123 95 0.09 0.09 0.09 0.09 0.000111 100 0.08 0.08 0.07 0.08 0.000100 Conclusion As you can see from the table of results and the graphs drawn, my prediction was right and that the further the distance, the smaller the output potential distance.

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

    3.28 3.0832 1.5 0.6 1.62 0.972 1 0 0 0 0.5 Here are the results for the second experiment, where the distance between the solar cell and light source was varied to see the power output on the solar cell.

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

    This diagram shows the experiment with the diffraction grating and the two lenses. The diagram shows the light passing through the diverging lens which splits it up and then going through the converging lens which concentrates the light to improve the accuracy and sharpness of the light on the screen.

  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. Refractive index by tracing light rays

    5. The glass block was removed and the marks were joined to meet CD at Q. The ray PQ in glass was completed and the normal at P was drawn as a dotted line. 6. The angle between PQ and this normal was measured and this is the critical angle (c)

  2. I am doing an investigation in to how much a metre rule bends when ...

    Resources from: Physics For You - pages 114 and 74 The Internet - www.studentcentral.co.uk Analysis: From the evidence shown we can clearly see that as the load (N) is increased, the extension (cm) becomes greater. This is because the heavier the load, the more it wants to fall to the ground and thus the greater the extension.

  1. Study the interference of light using Helium - Neon Diode Laser.

    two sources of light can only take place if they are coherent sources, that is they must have the same wavelength and be always in phase with each other or have a constant phase difference. Thus, implies that the two sources of light must have the same colour.

  2. Carry out a two source superposition of laser light experiment using a double slit, ...

    To work out the percentage uncertainties of measurements the following equation must be used absolute uncertainty x100 actual value The errors have been estimated as follows: d = 2.075m ? 0.002 Percentage uncertainty = 0.002 x 100 = 0.1% 2.075 s = 0.25mm ?

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