Investigation of the chromatic aberration of a converging lens.

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Investigation of the chromatic aberration of a converging lens

                                By Wen Yan Gao

Aim

To find the difference in focal length of a converging lens when used to produce images with red and blue light.

Planning

Background information

Chromatic aberration arises from dispersion- the property that the refractive index of glass differs with wavelength of light.

The focal length of a lens is determined by a combination of its geometry and the refractive index of the material from which it is made. The refractive index varies slightly with the wavelength of the light that is being transmitted. This means that the focal length of a lens will vary for different colours of light. For blue light (short wavelengths), the focal length is larger than that of red light (long wavelengths).

Prediction

It was predicted that the values of the focal length of the lens obtained from red and blue light are different, given that the standard focal length is 10cm.

Proposed Method:

The method is to use the lens formula.

1/f = 1/u +1/v

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To use this formula both the object distance (u) and the image distance (v) need to be measured. This method is not as simple as method 1 above, but the result obtained will be more accurate. Therefore, the focal length of a converging lens in this experiment was determined by method 2.

Detailed Procedures:

All the lights were switched off to ensure the laboratory was dark.

1.The apparatus were set up as shown in the diagram below. Some black cupboards were put surrounded the apparatus to provide light insulation.

2. The light bulb, object grill, appropriate light filter, lens, ...

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