Diffraction of light is more pronounced when
A Aperture ≫ wavelength
B Aperture ≈ wavelength
C Aperture = infinity
D Light is incoherent
Diffraction becomes significant when aperture size is comparable to λ.
Fraunhofer diffraction refers to
A Diffraction with source and screen at finite distances
B Diffraction with source at infinity and screen at infinity (parallel rays)
C Near-field diffraction
D Reflection only
Fraunhofer = far-field diffraction.
Fresnel diffraction refers to
A Far-field diffraction
B Near-field diffraction with curvature of wavefront important
C No diffraction
D Laser diffraction only
In single-slit Fraunhofer diffraction, minima occur when
A d sinθ = mλ
B a sinθ = mλ
C a sinθ = (m + ½)λ
D 2a sinθ = λ
Minima for single slit of width a: a sinθ = mλ.
The central maximum in single-slit diffraction is
A Narrower than side maxima
B Twice as wide as other maxima
C Equal width to other maxima
D Zero
Intensity in single-slit diffraction pattern is proportional to
A (sinβ/β)²
B cosβ
C tanβ
D sinβ
In single-slit diffraction, β =
A πa/λ sinθ
B a/λ
C θ/a
D None
Condition for principal maxima in single-slit diffraction is
A a sinθ = mλ
B a sinθ = (2m+1)λ/2
C No simple condition exists
D d sinθ = mλ
Secondary maxima positions require solving derivative, not a simple linear condition.
If slit width decreases in single-slit diffraction, the central maximum
A Narrows
B Widens
C Disappears
D Moves sideways
Diffraction effects dominate when
A Using very large lenses
B Aperture becomes small
C Light intensity increases
D Light is polarized
Double-slit diffraction pattern is
A Pure interference
B Pure diffraction
C Interference pattern modulated by single-slit diffraction envelope
D Random
In double-slit diffraction, fringe visibility decreases when
A Slits wider
B Slits narrower
C Wavelength decreases
D None
Wider slits → stronger diffraction minima → reduced interference contrast.
In diffraction gratings, principal maxima occur at
A a sinθ = mλ
B d sinθ = mλ
C 2d = mλ
D d/λ = m
Grating equation: d sinθ = mλ.
Grating resolving power is given by
A λ/d
B Nλ
C mN
D N/d
R=λ/Δλ=mN, where N = number of slits.
Diffraction grating gives very sharp maxima because
A Large number of slits interfere
B Wide slits
C Light intensity low
D Source is incoherent
In Fresnel diffraction, the shape of fringes depends on
A Aperture shape
B Wavelength
C Geometry of obstacle
D All the above
Fresnel zones are
A Concentric circles representing regions of constructive/destructive interference
B Spectral regions
C Lens coatings
D Polarized domains
A zone plate focuses light due to
A Refraction
B Reflection
C Diffraction
D Polarization
Zone plate uses constructive interference via diffraction.
A zone plate behaves like
A A diverging lens
B A converging lens (multiple focal points)
C Mirror
D Prism
In zone plate, the radii of zones follow
A rₙ ∝ n
B rₙ² ∝ n
C rₙ³ ∝ n
D rₙ constant
rₙ² = nλf.
Diffraction through circular aperture results in
A No pattern
B Airy pattern
C Newton’s rings
D White centre
Angular resolution of a telescope (Rayleigh criterion) is
A 1.22 λ/a
B a/1.22λ
C λ/a²
D d/λ
Reducing aperture diameter does what to resolution?
A Improves it
B Worsens it
C No effect
D Random
The resolving power of a grating increases with
A Number of slits
B Decreasing slits
C Wavelength
D None
Missing orders occur in double-slit diffraction when
A d sinθ = mλ
B a/d = integer ratio leading to cancellation of certain maxima
C λ very small
D Slits very narrow
Intensity at the central maximum of a single slit is approximately
A Four times the secondary maximum
B Half of it
C Same as side lobes
D Zero
Grating spacing d decreases when
A Slits decrease in number
B Slits per unit length increase
C λ increases
D Light intensity decreases
For equal slit widths, diffraction envelope depends on
A Slit separation
B Wavelength
C Individual slit width
D Number of slits
In multiple-slit diffraction, principal peaks become
A Narrower and more intense
B Broader and weaker
C Random
D Disappear
Half-period zones in Fresnel theory contribute
A Additively
B Alternately with opposite phases
C Nothing
D Only destructively
Obstructing alternate Fresnel zones (zone plate idea)
A Eliminates diffraction
B Enhances one constructive contribution → focusing
C Creates polarization
D Creates dispersion
In single-slit diffraction, if wavelength increases, the diffraction pattern
A Widens
B Narrows
C Disappears
D No effect
For a given aperture, shorter wavelengths give
A Better resolution
B Worse resolution
C No change
D Zero diffraction
The grating element (d) is
A Width of single slit
B Total width of slit + spacing
C Twice the slit width
D Always 1 mm
A transmission grating works due to
A Reflection
B Refraction
C Diffraction + interference
D Polarization filtering
In Fresnel diffraction at straight edge, fringes are
A Uniform
B Non-uniform, hyperbolic
C Circular
D Absent
Fraunhofer diffraction uses
A Divergent waves
B Plane-wave illumination (far field)
C Spherical waves
D No optical elements
The first minima in circular aperture diffraction occurs at angle satisfying
A a sinθ = λ
B 1.22 λ/D
C λ/2D
D D/λ
The energy in diffraction pattern is
A Lost
B Redistributed
C Constant only at centre
D Infinite
In multi-slit interference, secondary maxima
A Strong
B Very weak
C Equal to main maxima
D Random
The free spectral range of a grating is
A λ²/d
B λ/m
C d/λ
D λ/N
FSR = λ/m for grating order m.
A zone plate exhibits
A Chromatic aberration
B No focusing properties
C Monochromatic focus only
D Infinite focal points
Higher orders in diffraction grating appear at
A Smaller angles
B Larger angles
C No angle
D Always zero angle
If grating is illuminated with white light, different wavelengths
A Overlap
B Separate into spectra
C Disappear
D Become monochromatic
Diffraction efficiency depends strongly on
A Groove shape
B Wavelength
C Incidence angle
D All of these
Fresnel’s half-period theory explains
A Why diffraction cannot occur
B Why contributions partially cancel
C Why central maximum is bright
D Both B and C
In single-slit diffraction, if slit width doubles, width of central maximum
A Doubles
B Halves
C Increases four times
D Unchanged
Zone plate focal length decreases when
A Wavelength increases
B Zone radii decrease
C Zone spacing constant
D All above
f = r₁²/λ → dependent on λ and radii.
Grating with 600 lines/mm has grating spacing
A 1/600 mm
B 600 mm
C 0.6 mm
D 6 mm
d = 1/600 mm.
A circular aperture produces
A Rectangular diffraction
B Airy disc pattern
C Flat-top pattern
D Random fringes