JEE Main 2015 · 10 Apr · Shift 1 · Physics Q25

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PhysicsSingle correct+4 / -1Question 25 of 90

A parallel beam of electrons travelling in $x$ -direction falls on a slit of width d (see figure). If after passing the slit, an electron acquires momentum $p_y$ in the $y$ -direction then for a majority of electrons passing through the slit (h is Planck's constant) :

A parallel beam moving in +x strikes a barrier with a slit of width d; Y and X axes are marked.

|p_y|d\simeq h

|p_y|d>h

|p_y|d<h

|p_y|d>>h

Answer and worked solution

Official answer: C

By the uncertainty principle the spread in $p_y$ is of order $\frac hd$ . Most electrons fall within the central diffraction maximum, where $|p_y|<\frac hd$ , i.e. $|p_y|d<h$ .

Topics:de Broglie waves Diffraction

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JEE Main 2015 · 10 Apr · Shift 1, Physics question 25