Interference and Young's double-slit experiment — practice questions

Question 1 · difficulty L1 · recall

Interference results from

• A. superposition of coherent waves
• B. absorption of one wave by another
• C. reflection from only one surface
• D. random addition with no phase relation

Question 2 · difficulty L1 · understanding

For constructive interference, path difference is

• A. (m+1/2)λ
• B. mλ
• C. λ/4 only
• D. always zero and no other value

Question 3 · difficulty L2 · understanding

For destructive interference, path difference is

• A. mλ
• B. 2mλ only
• C. (m+1/2)λ
• D. λ²/d

Question 4 · difficulty L2 · application

In Young's double-slit experiment, fringe width is

• A. β=dD/λ
• B. β=λd/D
• C. β=D/(λd)
• D. β=λD/d

Question 5 · difficulty L3 · application

If wavelength is doubled in YDSE with D and d fixed, fringe width

• A. doubles
• B. halves
• C. quadruples
• D. stays unchanged

Question 6 · difficulty L3 · application

If slit separation d is doubled in YDSE, fringe width

• A. doubles
• B. halves
• C. quadruples
• D. stays unchanged

Question 7 · difficulty L4 · analysis

At the central point equidistant from two coherent in-phase slits, the interference is

• A. destructive
• B. random
• C. constructive
• D. necessarily zero intensity

Question 8 · difficulty L4 · analysis

If one YDSE slit is covered, the regular two-slit interference fringes

• A. become twice as closely spaced two-slit fringes
• B. remain identical
• C. turn into only dark fringes
• D. disappear

Question 9 · difficulty L5 · analysis

A YDSE setup has λ=600 nm, D=2 m and d=0.50 mm. Fringe width is

• A. 2.4 mm
• B. 0.24 mm
• C. 24 mm
• D. 1.2 mm

Question 10 · difficulty L5 · analysis

Two coherent waves of equal amplitude reach a point with phase difference π. The resultant intensity ideally is

• A. four times one-wave intensity
• B. zero
• C. twice one-wave intensity
• D. equal to one-wave intensity