IIT-JEE 2007 · Paper 2 · Physics Q18

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PhysicsSingle correct+4 / -1Question 18 of 66

Passage

Paragraph for Question Nos. 17 to 19

The figure shows a surface XY separating two transparent media, medium-1 and medium-2. The lines ab and cd represent wavefronts of a light wave travelling in medium-1 and incident on XY. The lines ef and gh represent wavefronts of the light wave in medium-2 after refraction.

(Figure: parallel straight wavefronts ab and cd in medium-1 above the boundary XY, and parallel straight wavefronts ef and gh in medium-2 below it, closer together and inclined differently.)

(The paragraph is not printed in the official archive copy (which reproduces only the questions with their answers); its text is restored from the JEE 2007 question paper.)

The phases of the light wave at $c$ , $d$ , $e$ and $f$ are $\phi_c$ , $\phi_d$ , $\phi_e$ and $\phi_f$ respectively. It is given that $\phi_c\ne\phi_f$ .

\phi_c

cannot be equal to

\phi_d

\phi_d

can be equal to

\phi_e

(\phi_d-\phi_f)

is equal to

(\phi_c-\phi_e)

(\phi_d-\phi_c)

is not equal to

(\phi_f-\phi_e)

Answer and worked solution

Official answer: C

Same wavefront, same phase. $c$ and $d$ lie on wavefront cd, so $\phi_c=\phi_d$ ; $e$ and $f$ lie on wavefront ef, so $\phi_e=\phi_f$ .

So $\phi_d-\phi_f=\phi_c-\phi_e$ . ((A) and (D) contradict $\phi_c=\phi_d$ ; (B) would need $\phi_c=\phi_f$ , which is excluded.)

(C)

Topics:Huygens' principle

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IIT-JEE 2007 · Paper 2, Physics question 18