Stars twinkle because
Options:
A.the intensity of light emitted by them changes with time.
B.the distance of the stars from the earth changes with time.
C.the refractive index of the different layers of the earth's atmosphere changes continuously.
D.None of these
Answer: Option C

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More Questions on This Topic :

Question 1. Suitable impurities are added to a semiconductor depending on its use. This is done in order to
  1.    increase its life
  2.    enable it to withstand higher voltages
  3.    increase its electrical conductivity
  4.    increase its electrical resistivity
Answer: Option C
Question 2. It takes much longer to cook food in the hills than in the plains, because
  1.    in the hills the atmospheric pressure is lower than that in the plains and therefore water boils at a temperature lower than 100oC causing an increase in cooking time
  2.    due to low atmospheric pressure on the hills, the water boils at a temperature higher than 100oC and therefore water takes longer to boil
  3.    in the hills the atmospheric density is low and therefore a lot of heat is lost to the atmosphere
  4.    in the hills the humidity is high and therefore a lot of heat is absorbed by the atmosphere leaving very little heat for cooking
Answer: Option A
Question 3. Moment of inertia is:
  1.    Vector
  2.    Scalar
  3.    Phasor
  4.    Tensor
Answer: Option D
Question 4. On a clean glass plate a drop of water spreads to form a thin layer whereas a drop of mercury remains almost spherical because:
  1.    mercury is a metal.
  2.    density of mercury is greater than that of water.
  3.    cohesion of mercury is greater than its adhesion with glass.
  4.    cohesion of water is greater than its adhesion with glass.
Answer: Option C
Question 5. Sound of frequency below 20 Hz is called
  1.    audio sounds
  2.    infrasonic
  3.    ultrasonic
  4.    supersonics
Answer: Option B
Question 6. RADAR is used for:
  1.    locating submerged submarines.
  2.    receiving a signals in a radio receiver.
  3.    locating geostationary satellites.
  4.    detecting and locating the position of objects such as Aeroplanes.
Answer: Option D