JEE Main · 2021 · 26 Feb 2021 · Shift 1 · Modern Physics

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Given below are two statements : one is labelled as Assertion A and the other is labeled as Reason R.
Assertion A : An electron microscope achieve better resolving power than an optical microscope.
Reason R : The de Broglie's wavelength of the electrons emitted from an electron gun is much less than wavelength of visible light.
In the light of the above statements, choose the correct answer from the options given below :

(A) $A$ is true but $R$ is false.
(B) $A$ is false but $R$ is true.
(C)Both $A$ and $R$ are true and $R$ is the correct explanation of $A$ .✓ Correct
(D)Both $A$ and $R$ are true but $R$ is NOT the correct explanation of $A$ .

Answer: (C)

Solution

The smallest separation a microscope can resolve is

d = \frac{λ}{2 μ s i n θ}

, so the resolving power

\frac{1}{d}

rises as the wavelength falls. Electrons leaving an electron gun after acceleration through a few tens of kilovolts have de Broglie wavelength

λ = \frac{h}{p}

of the order of

1 0^{- 2}

nm, against roughly

400

700

nm for visible light. This far shorter wavelength is exactly why the electron microscope separates finer detail than an optical one, so both the assertion and the reason are true and the reason is the correct explanation of the assertion.

JEE Main · 2021 · 26 Feb 2021 · Shift 1 · Single correct option

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JEE Main · 2021 · 26 Feb 2021 · Shift 1 · Modern Physics

Solution

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