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8. Electromagnetic waves — Physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 SciencePhysics8. Electromagnetic waves1 Mark
MCQ
Given below are two statement: one is labelled as Assertion $A$ and the other is labelled as Reason $R.$

Assertion $A:$ $EM$ waves used for optical communication have longer wavelengths than that of microwave, employed in Radar technology.

Reason $R$ : Infrared $EM$ waves are more energetic than microwaves, (used in Radar)

In the light of given statements, choose the correct answer from the options given below:

  • ✓
    $A$ is false but $R$ is true
  • B
    $A$ is true but $R$ is false
  • C
    Both $A$ and $R$ true but $R$ is $NOT$ the correct explanation of $A$
  • D
    Both $A$ and $R$ true and $r$ is the correct explanation of $A$
✓

Answer

Correct option: A.
$A$ is false but $R$ is true
a
Optical communication is performed in the frequency range of $1\,THz$ to $1000\,THz$.

(Microwave to $UV$)

So,$EM$ waves used for optical communication have shorter wavelength than that of microwaves used in $RADAR.$

Also, $v_{\text {INFRARED }}>v_{\text {MICROWAVE }}$

$\therefore$ Infrared $EM$ waves are more energetic than microwave

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