The law of reflection states that the angle of incidence equals the angle of
A Refraction
B Reflection
C Deviation
D Diffraction
By definition: θ₁ = θr measured from the normal.
Snell’s law relates refractive indices as
A n₁sinθ₁ = n₂sinθ₂
B n₁/n₂ = sinθ₁/sinθ₂
C n₁sinθ₂ = n₂sinθ₁
D n₁cosθ₁ = n₂cosθ₂
Standard Snell’s law: n₁ sinθ₁ = n₂ sinθ₂.
When light goes from a denser to rarer medium, total internal reflection occurs if incidence angle
A < critical angle
B = 0
C > critical angle
D = Brewster angle
TIR occurs for θ > θc, where sinθc = n₂/n₁ (n₁>n₂).
The focal length of a thin lens depends on
A Lens material and curvature
B Wavelength only
C Only lens thickness
D Surrounding temperature only
Lensmaker’s formula: 1/f = (n−1)(1/R1 − 1/R2).
A convex lens produces a virtual image when object is placed
A At infinity
B Beyond 2f
C Between f and lens
D At 2f
Object inside focal length → virtual, upright, magnified image.
For a plane mirror, image distance equals
A Twice object distance
B Same as object distance
C Half the object distance
D Independent of object position
Plane mirror forms virtual image symmetric to object.
Magnification of a thin lens is given by
A v/u
B f/u
C -v/u
D u/v
Lateral magnification m = -v/u (sign indicates orientation).
Combination of two thin lenses in contact has equivalent focal length
A f1 + f2
B (f1 f2)/(f1+f2)
C f1 – f2
D Square root of product
For thin lenses in contact: 1/f = 1/f1 + 1/f2.
A concave mirror forms a real inverted image when the object is placed
A Inside focal length
B Between focus and pole
C Beyond focal point
D At pole
Object beyond focal point yields real inverted image.
The aperture stop of an optical system primarily limits
A Resolution only
B Field of view only
C Amount of light (brightness) and numerical aperture
D Focal length
Aperture controls light-gathering and affects NA and depth of field.
Chromatic aberration in a lens arises because
A Lens shape varies with radius
B Refractive index depends on wavelength
C Lenses are imperfectly polished
D Light intensity variations
Dispersion causes focal length to vary with wavelength.
Spherical aberration is caused by
A Non-paraxial rays focusing differently from paraxial rays
B Chromatic dispersion
C Polarization effects
D Interference fringes
Rays far from axis focus at different points than paraxial rays.
In an astronomical telescope (refracting), image formed by objective is
A Virtual and upright
B Real and inverted at focal plane of eyepiece
C Real and at infinity for normal viewing
D Imaginary
For astronomical telescope in normal adjustment, objective forms real image at eyepiece focal plane; final image at infinity.
Resolving power of an optical instrument generally improves with
A Decreasing aperture
B Increasing aperture
C Increasing wavelength
D Random noise
Rayleigh criterion: resolution θmin ≈ 1.22 λ/D → larger D better.
A virtual image can be formed by
A Convex mirror
B Concave lens
C Convex lens with object inside f
D All of the above
All these can produce virtual images in appropriate configurations.
When light enters a glass slab from air, phase of transmitted wave is
A Always unchanged
B Delayed relative to air (phase lag)
C Advanced
D Randomized
Optical path length increases → phase retardation compared to air.
Newton’s formula for spherical mirrors relates object and image distances as
A (1/v) − (1/u) = 1/f
B xm xn = f²
C x (image) + x (object) = 2f
D (1/u) + (1/v) = 1/f
Standard mirror/lens equation 1/u + 1/v = 1/f.
Power of a lens is given in diopters as
A f (m)
B 1/f (m)
C f²
D -1/f (cm)
Power P = 1/f (in metres).
A ray close to the axis is called a
A Marginal ray
B Chief ray
C Paraxial ray
D Diffracted ray
Paraxial rays are small-angle rays approximated by paraxial optics.
The optic center of a thin lens is the point where a ray passing through
A Is refracted at maximum
B Passes undeviated
C Is totally internally reflected
D Becomes polarized
Ray through optic center emerges parallel to itself (neglecting thickness).
Myopia (nearsightedness) is corrected by
A Convex lens
B Concave lens
C Cylindrical lens only
D Polarizer
Diverging (concave) lens shifts image to retina.
Magnifier (simple microscope) gives angular magnification ≈
A 1
B f (m)
C 25 cm / f (for near point 25 cm)
D f/25 cm
Angular magnification ≈ D / f where D ≈ 25 cm (least distance of distinct vision).
A ray that passes through the center of curvature of a spherical mirror reflects back along
A Same path
B Different path
C Perpendicular to incident
D Random direction
Incidence normal to surface (through center) → reflection back along same path.
For a thin lens, sign convention: image formed on opposite side of incoming light is
A Positive v
B Negative v
C Zero
D Undefined
Standard sign conventions: real image positive.
A converging lens produces a real magnified image when object is placed at
A At infinity
B At 1.5f (between f and 2f)
C At 2f
D Inside focal length
Between f and 2f → real, inverted, magnified image.
Aperture stop reduces
A Spherical aberration only
B Amount of light and depth of field
C Chromatic aberration only
D Polarization
Aperture affects brightness and depth of field; aberrations too.
A prism disperses white light because
A Refractive index varies with wavelength
B Prism has variable thickness
C Prism emits light
D Polarization effects
Dispersion due to n(λ) dependence.
In a lens, coma is an aberration that affects
A On-axis point images only
B Off-axis point images causing comet-like tails
C Chromatic dispersion
D Polarization
Coma distorts off-axis points.
The effective focal length of a plano-convex lens (plano side toward image) is best when used
A In air only
B With curved surface toward collimated beam
C With plane surface toward collimated beam
D In water only
For minimizing spherical aberration when focusing a parallel beam, plane surface faces the collimated beam.
Field curvature in imaging causes
A Sharp image across flat sensor
B Image plane to be curved so edges go out of focus on flat sensor
C Color fringes
D Increased magnification only
Field curvature makes best focus lie on a curved surface.
A lens with negative focal length is called
A Convex
B Concave (diverging)
C Biconvex
D Achromatic
The principal plane of a thick lens is used for
A Measuring polarization
B Simplifying ray tracing by using effective thin lens position
C Generating interference fringes
D Increasing focal length
In a Galilean telescope the eyepiece is
A Converging lens
B Diverging lens
C Mirror
D Prism
Galilean uses a concave eyepiece (diverging) producing upright image.
An achromatic doublet corrects chromatic aberration by combining
A Two identical crown glasses
B Crown and flint glasses of different dispersion
C Glass and plastic
D Lens and prism
In imaging systems, numerical aperture (NA) is proportional to
A sin θ (half-angle of acceptance) × n (refractive index)
B Wavelength only
C Focal length only
D Magnification only
Principal focus of a mirror is located at a distance f where f =
A R
B R/2
C 2R
D √R
For spherical mirror, focal length f = R/2.
A camera uses a diaphragm primarily to control
A Exposure (light amount) and depth of field
B Chromatic aberration
C Polarization
D Diffraction only
The magnification of a microscope depends on
A Objective and eyepiece focal lengths and tube length
B Only eyepiece
C Only objective
D Ambient light intensity
A paraxial approximation assumes sinθ ≈
A θ (in radians)
B 1
C θ²
D 0
For a converging lens forming a real image, the image distance v becomes negative when using
A Cartesian sign convention for virtual images
B No consistent sign convention
C Using Gaussian optics only
D None
Chromatic focal shift is minimized in achromats by making net dispersion
A Zero at two wavelengths (typically red & blue)
B Infinite
C Equal to focal length
D Random
In a reflecting telescope (Newtonian), the primary mirror is
A Convex
B Concave parabolic (often)
C Plano
D Cylindrical
The exit pupil of an optical instrument is the image of the
A Objective as seen through eyepiece
B Eyepiece as seen through objective
C Object itself
D Aperture stop only
A beam of light passing obliquely through a slab emerges
A Displaced laterally but parallel to incident direction
B Reversed direction
C Randomly polarized
D Split into two rays only
In a thin lens, if object is at 2f, image is formed at
A f
B 2f (same distance)
C Infinity
D At lens
Stereoscopic vision is aided by two eyes because they provide
A Two identical images only
B Parallax (different viewpoints) enabling depth perception
C Polarization detection
D Enhanced diffraction
A ray that strikes the lens at the edge is called a
A Paraxial ray
B Marginal ray
C Chief ray
D Diffracted ray
The chief ray (principal ray) passes through the
A Optic center only
B Edge of aperture stop and through center of image
C Center of curvature only
D Focal point only
For best image quality, optical systems are designed to minimize
A Only chromatic aberration
B Only spherical aberration
C All Seidel (primary) aberrations including coma, astigmatism, field curvature, distortion, spherical, chromatic
D Polarization
The back focal length of a lens is measured from
A Lens front surface to focal point
B Rear principal plane to focal point on image side
C Center of curvature to image
D Object to lens