1
GATE ECE 1993
+2
-0.6
An optical fiber consists of a cylindrical dielectric rod of refractive index $$n_1$$, surrounded by another dielectric of refractive index $$n_2$$ where $$n_2$$ < $$n_1$$ as shown in the following Fig. If a ray is incident from air at angle i to the axis, then it undergoes total internal reflection at the interface AB if
A
$$i\,\, \ge \,\,{\sin ^{ - 1}}\,\sqrt {{n_1}^2 - {n_2}^2}$$
B
$$i\,\, < \,\,{\sin ^{ - 1}}\,\sqrt {{n_1} - {n_2}}$$
C
$$i\,\, \le \,\,{\sin ^{ - 1}}\,\sqrt {{n_1}^2 - {n_2}^2}$$
D
$$i\,\, = \,\,{\sin ^{ - 1}}\,\sqrt {{n_1} - {n_2}}$$
2
GATE ECE 1990
MCQ (More than One Correct Answer)
+2
-0.6
Choose the correct statements.
For a wave propagating in an air filled rectangular wave guide
A
Guided wavelength is never less than the free space wavelength
B
Wave impedance is never less than the free space impedance.
C
Phase velocity is never less than the free space velocity
D
TEM mode is possible if the dimensions of the wave guide are properly chosen.
3
GATE ECE 1988
MCQ (More than One Correct Answer)
+2
-0.6
For a normal mode EM wave propagating in a hollow rectangular wave guide
A
the phase velocity is greater than the group velocity
B
the phase velocity is greater than velocity of light in free space
C
the phase velocity is less than the velocity of light in free space
D
the phase velocity may be either greater than or less than the group velocity
4
GATE ECE 1987
MCQ (More than One Correct Answer)
+2
-0.6
The cut-off frequency of a waveguide depends upon
A
The dimensions of the waveguide
B
The dielectric property of the medium in the waveguide
C
The characteristic impedance of the waveguide
D
The transverse and axial components of the fields
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