Question

Assertion :An electron beam is used to obtain interference in a simple young's double-slit experiment arrangement with appropriate distance between the slits. If the speed of electrons is increased, the fringe width decreases Reason: de Broglie wavelength of electron is inversely proportional to the speed of the electrons

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

De Broglie wavelength of electron is given by $\lambda =\frac{h}{p}$

Hence more the speed, less the $\lambda$

Fringe width $\beta =\lambda \frac{D}{d}$

So less the $\lambda$ less the fringe width. Therefore on incresing speed of electron the fringe width decreases.

So, the answer is option (A).