1. A monochromatic wave propagates along a waveguide in z direction. These points of constant phase travel in constant phase travel at a phase velocity Vp is given by?
a) Vp=ω/c
b) Vp=ω/β
c) Vp=mass/acceleration
d) Vp=C/N
Explanation: Velocity is a function of displacement. Phase velocity Vp is a measure of angular velocity.
2. The phenomenon which occurs when an incident wave strikes an interface at an angle greater than the critical angle with respect to the normal to the surface is called as ____________
a) Refraction
b) Limiting case of refraction
c) Total internal reflection
d) Partial internal reflection
Explanation: Total internal reflection takes place when the light wave is in the more dense medium and approaching towards the less dense medium. Also, the angle of incidence is greater than the critical angle. Critical angle is an angle beyond which no propagation takes place in an optical fiber.
3. For lower bandwidth applications ______________
a) Photonic crystal fibers are advantageous
b) Coaxial cables are advantageous
c) Single mode fiber is advantageous
d) Multimode fiber is advantageous
Explanation: In multimode fibers, intermodal dispersion occurs. The group velocities often differ which gradually restricts maximum bandwidth attainability in multimode fibers.
4. Meridional rays in graded index fibers follow ____________
a) Curved path along the axis
b) Straight path along the axis
c) Helical path
d) Path where rays changes angles at core-cladding interface
Explanation: Meridional rays pass through axis of the core. Due to the varying refractive index at the core, the path of rays is in curved form.
5. When λ is the optical wavelength in vacuum, k is given by k=2Π/λ. What does k stand for in the above equation?
a) Phase propagation constant
b) Free-space constant
c) Dielectric constant
d) Boltzmann’s constant
Explanation: In the above equation, k = 2Π/λ, also termed as wave equation, k gives us the direction of propagation and also the rate of change of phase with distance. Hence it is termed as phase propagation constant.
6. When light is described as an electromagnetic wave, it consists of a periodically varying electric E and magnetic field H which are oriented at an angle?
a) Less than 90 degree
b) Greater than 90 degree
c) 90 degree to each other
d) 180 degree apart
Explanation: In case of electromagnetic wave which occur only in presence of both electric and magnetic field, a particular change in magnetic field will result in a proportional change in electric field and vice versa. These changes result in formation of electromagnetic waves and for electromagnetic waves to occur both fields should be perpendicular to each other in direction of wave travelling.
7. What is the unit of normalized frequency?
a) Coulombs
b) Meter/sec
c) Hertz
d) It is a dimensionless quantity
Explanation: Normalized frequency of optical fiber is the frequency which exists at cut-off condition. There is no propagation and attenuation above cut-off. It is directly proportional to numerical aperture which is a dimensionless quantity; hence itself is a dimensionless quantity.
8. Which equations are best suited for the study of electromagnetic wave propagation?
a) Avrami equations
b) Maxwell’s equations
c) Boltzmann’s equations
d) Allen-Cahn equations
Explanation: Electromagnetic mode theory finds its basis in electromagnetic waves. Electromagnetic waves are always represented in terms of electric field E, magnetic field H, electric flux density D and magnetic flux density B. These set of equations are provided by Maxwell’s equations.
9. Which is the most important velocity in the study of transmission characteristics of optical fiber?
a) Average velocity
b) Group velocity
c) Phase velocity
d) Normalized velocity
Explanation: Group velocity is much important in relation to transmission characteristics of optical fiber. This is because the optical wave propagates in groups or form of packets of light.
10. Constructive interference occur when total phase change after two successive reflections at upper and lower interfaces is equal to? (Where m is integer)
a) 2Πm
b) Πm/4
c) Πm/6
d) Πm
Explanation: The component of phase waves which is in x direction is reflected at the interference between the higher and lower refractive index media. It is assumed that such an interference forms a lowest order standing wave, where electric field is maximum at the center of the guide, decaying towards zero.