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question_answer1) Assertion : Diode lasers are used as optical sources in optical communication. Reason : Diode lasers consume less energy. [AIIMS 2005]
question_answer2) Assertion : Television signals are received through sky-wave propagation. Reason : The ionosphere reflects electromagnetic waves of frequencies greater than a certain critical frequency. [AIIMS 2005]
question_answer3) Assertion : In high latitude one sees colourful curtains of light hanging down from high altitudes. Reason : The high energy charged particles from the sun are deflected to polar regions by the magnetic field of the earth. [AIIMS 2003]
question_answer4) Assertion : Short wave bands are used for transmission of radio waves to a large distance. Reason : Short waves are reflected by ionosphere [AIIMS 1994]
question_answer5) Assertion : The electrical conductivity of earth's atmosphere decreases with altitude. Reason : The high energy particles (i.e. g-rays and cosmic rays) coming from outer space and entering our earth's atmosphere cause ionisation of the atoms of the gases present there and the pressure of gases decreases with increase in altitude.
question_answer6) Assertion : The electromagnetic waves of shorter wavelength can travel longer distances on earth's surface than those of longer wavelengths. Reason : Shorter the wavelength, the larger is the velocity of wave propagation.
question_answer7) Assertion : The surface wave propagation is used for medium wave band and for television broadcasting. Reason : The surface waves travel directly from transmitting antenna to receiver antenna through atmosphere.
question_answer8) Assertion : The television broadcasting becomes weaker with increasing distance. Reason : The power transmitted from TV transmitter varies inversely as the distance of the receiver
question_answer9) Assertion : Microwave propagation is better than the sky wave propagation. Reason : Microwaves have frequencies 100 to 300 GHz, which have very good directional properties.
question_answer10) Assertion : Satellite is an ideal platform for remote sensing. Reason : Satellite in polar orbit can provide global coverage or continuous coverage of the fixed area in geostationary configuration.
question_answer11) Assertion : Fax is a modulating and demodulating device. Reason : It is necessary for exact reproduction of a document.
question_answer12) Assertion : A dish antenna is highly directional. Reason : This is because a dipole antenna is omni directional.
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