Q78.Consider telecommunication through optical fibres. Which of the following statements is not true? (1) Optical fibres can be of graded refractive index (2) Optical fibres are subjective to electromagnetic interference from outside (3) Optical fibres have extremely low transmission (4) Optical fibres may have homogeneous core with loss a suitable cladding.

Q29.This question has Statement −1 and Statement −2. Of the four choices given after the statements, choose the one that best describes the two statements. Statement-1 : Sky wave signals are used for long distance radio communication. These signals are in general, less stable than ground wave signals. Statement-2 : The state of ionosphere varies from hour to hour, day to day and season to season. (1) Statement-1 is true, Statement-2 is true; (2) Statement-1 is true, Statement-2 is true; Statement-2 is the correct explanation of Statement-2 is not the correct explanation of Statement-1. Statement-1. (3) Statement- 1 is false, Statement- 2 is true. (4) Statement-1 is true, Statement-2 is false. JEE Main 2011 JEE Main Previous Year Paper

Q30.Broadcasting antennas are generally (1) vertical type (2) both vertical and horizontal type (3) omni directional type (4) horizontal type

Q29.Given the electric field of a complete amplitude modulated wave as Em →E = ^iEc + cos cos ωct (1 Ec ωmt) Where the subscript c stands for the carrier wave and m for the modulating signal. The frequencies present in the modulated wave are (1) ωc and √ω2c + ω2m (2) ωc, ωc + ωm and ωc −ωm (3) ωc and ωm (4) ωc and √ωcωm