CBSE Questions for Class 12 Medical Physics Electromagnetic Waves Quiz 12 - MCQExams.com

A vehicle carries a microwave transmitter that emits microwaves of a constant frequency. A
stationary observer has a microwave receiver.
The vehicle moves directly towards the observer at constant speed. The observer detects
microwaves of frequency $$F_o$$.
The vehicle then accelerates, still moving towards the observer, travels at higher steady speed
for a time and then decelerates until it stops.
What is the variation in the frequency of the microwaves that are detected by the observer? 
  • The observed frequency will fall, then remain steady then return to the frequency $$F_o$$.
  • The observed frequency will fall, then remain steady then rise to a higher frequency than $$F_o$$.
  • The observed frequency will rise, then remain steady then fall to a lower frequency than $$F_o$$.
  • The observed frequency will rise, then remain steady then return to the frequency $$F_o$$.
Finger prints on a piece of paper may be detected by sprinkling fluorescent powder on the paper and then looking it into.
  • Mercury light
  • Sunlight
  • Infrared light
  • Ultraviolet light
Assertion : The electrical conductivity of earths atmosphere decrease with altitude.
Reason : The high energy particles (i.e. $$\gamma-$$ rays and cosmic rays) coming from outer space and entering our earths atmosphere causes ionisation of the atoms of the gases present there and the pressure of gases decreases with increase in altitude.
  • Both assertion and reason are true and the reason is the correct explanation of the assertion.
  • Both assertion and reason are true but reason is not the correct explanation of the assertion.
  • Assertion is true but reason is false.
  • Assertion and reason both are false.
  • Assertion is false but reason is true.
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