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We wish to see inside an atom. Assuming ...

We wish to see inside an atom. Assuming the atom to have a diameter of `100` pm, this means that one must be able to resolve a width of say `10` pm. If an electron microscope is used, the minimum electron energy required is about

A

1.5 keV

B

15 KeV

C

150 keV

D

1.5 MeV.

Text Solution

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The correct Answer is:
B
In electron microscope,electrons are used as the 'light source'.The resolving power of a microscope is approximately equal to that of wavelength of the light used.The de broglie wavelength `lamda`of a particle is related to its momentum p by
`lamda=(h)/(p)=(h)/(mv)`
The speed of required electron is
`v=(h)/(mlamda)=(6.63xx10^(-34)Js)/(9.11xx10^(-31)kg 10^(-11)m)=7.28xx10^(7)`m/s
The corresponds to kinetic energy of`R=(1)/(2)mv^(2)`
`=(1)/(2)xx9.11xx10^(-31)xx(7.28xx10^(7))^(2)xx(1 eV)/(1.6xx10^(-19)J)`ltbrge15.1 keV.
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The limit of resolution of a microscope is the least distance between two point objects which can be seen clearly and distinctively with it. For a naked eye, limit of resolution is about 10^(-4) m or 0.1 mm. The limit of resolution for a microscope is of the order of lambda/2 , where lambda is wavelength of light used. For an optical microscope , using visible light, limit of resolution is "500 nm"/2 =250 mm. This is 400 times smaller than naked eye. So the useful magnification produced by it is 400. Smaller is the limit of resolution, greater is the magnification that can be achieved. By using shorter wavelengths , we can improve resolution. For examination of a microorganism, much higher limit of resolution is needed, the Wave nature of electron provides a means for probes of very small size organisms. An electron beam accelerated by a high potential difference possess a very short wavelength. In an electron microscope magnetic lenses are used to control the path of electrons. The image of object is obtained on a fluorescent screen or on a photographic plate. The electron microscope with its high magnifying power and resolving power , is one of the most indispensable and powerful tool for research in science , medicine and industry. The working of an electron microscope uses properties of electrons related to

The limit of resolution of a microscope is the least distance between two point objects which can be seen clearly and distinctively with it. For a naked eye, limit of resolution is about 10^(-4) m or 0.1 mm. The limit of resolution for a microscope is of the order of lambda/2 , where lambda is wavelength of light used. For an optical microscope , using visible light, limit of resolution is "500 nm"/2 =250 mm. This is 400 times smaller than naked eye. So the useful magnification produced by it is 400. Smaller is the limit of resolution, greater is the magnification that can be achieved. By using shorter wavelengths , we can improve resolution. For examination of a microorganism, much higher limit of resolution is needed, the Wave nature of electron provides a means for probes of very small size organisms. An electron beam accelerated by a high potential difference possess a very short wavelength. In an electron microscope magnetic lenses are used to control the path of electrons. The image of object is obtained on a fluorescent screen or on a photographic plate. The electron microscope with its high magnifying power and resolving power , is one of the most indispensable and powerful tool for research in science , medicine and industry. The advantage of electron microscope over optical microscope is that

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