The figures above are reproduced from the text. D is the diameter of the objecti

Question

The figures above are reproduced from the text. D is the diameter of the objective lens that is a distance L from the microscope slide in a medium of index of refraction n. Half the acceptance angle for the lens is alpha and the physical distance between the two spots on the slide to be resolved (right figure) is x (figure is not to scale). Let the NA of the objective lens be 1.35. The lens is an oil immersion lens, making the index of refraction 1.5. The distance between the lens and the slide is 1.6 cm. What is the diameter D of the lens? _______ cm The diameter of the lens D in the previous problem is reduced by 0.5 cm. However, the resolution of the image must stay the same, so a new wavelength of light must be used to create the image. The wavelength of light used with the original lens is 550 nm in vacuum. What is the new wavelength of light in the oil immersion? _______ nm Which of the following are true about resolution in microscopy?

Explanation / Answer

Given NA=1.35

The numerical aperture of a lens is defined as

NA=nosin =1.5sin

or Sin =1.35/1.5

=64.15

where is half the angle, and n is the refractive index of the medium between the lens and specimen

(The space between the objective lens and the specimen is filled with oil .This is why because oil has a refractive index greater than 1)

tan =(D/2)/L

thus D/2=64.15*1.6==102.6

OR D=205.3 cm

b) A measure of the resolving power x

x=wavelenght/2*NA

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