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Question

In an electron microscope, the resolution that can be achieved is of the order of the wavelength of electrons used. To resolve a width of 7.5×10-12m, the minimum electron energy required is close to :


A

1keV

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B

25keV

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C

500keV

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D

100keV

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Solution

The correct option is B

25keV


Explanation for correct option:

Option (b) 25keV

Step 1: Given data

  • Given wavelength =7.5×10-12m
  • Mass of electron =9.1×10-31Kg

Step 2: Formula used

  • By using the De Broglie equation:

λ=hP

  • P=hλ
  • Now, to find Kinetic energy, we use the formula given below:
  • KE=P22m=(h/λ)22m

Step 3: Find Kinetic Energy

  • Now, we will substitute the given values in the formula given below:

KE=(hλ)22m

K.E.=6.6×10-347.5×10-122×9.1×10-31

K.E.=25keV

Thus, the minimum electron energy required is 25keV


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