CHEMISTRY · Single correct · ISC · Chemistry · Classification of Elements and Periodicity in Properties · Structure of Atom
Problem
Which of the following statement is NOT correct?
(1) Ground wave signals are more stable than the sky wave signals.
(2) The critical frequency of an ionospheric layer is the highest frequency that will be reflected back by the layer when it is vertically incident.
(3) Electromagnetic waves of frequencies higher than about 30 MHz cannot penetrate the ionosphere.
(4) Sky wave signals in the broadcast frequency range are stronger at night than in the day time.