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Electromagnetic Waves question

2023 · 12 Apr · Shift 1 · Q47
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  5. /2023 · 12 Apr · Shift 1 · Q47

Electromagnetic Waves question

2023 · 12 Apr · Shift 1 · Q47

JEE MainPhysicsElectromagnetic WavesMCQ+4 / −1
Given below are two statements: one is labelled as Assertion A\mathbf{A}A and the other is labelled as Reason R\mathbf{R}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.
  1. A
    Both A\mathrm{A}A and R\mathrm{R}R are true but R\mathrm{R}R is NOT the correct explanation of A\mathrm{A}A
  2. B
    A\mathrm{A}A is true but R\mathrm{R}R is false
  3. C
    Both A\mathrm{A}A and R\mathrm{R}R are true and r\mathrm{r}r is the correct explanation of A\mathrm{A}A
  4. D
    A\mathrm{A}A is false but R\mathrm{R}R is true
View written solutionFree

Correct answer: D

  1. Analyze Assertion A

    Assertion A says:

    EM waves used for optical communication have longer wavelengths than microwaves used in radar.

    Optical communication generally uses infrared/light waves. Radar uses microwaves.

    In the electromagnetic spectrum: λinfrared<λmicrowave\lambda_{\text{infrared}} < \lambda_{\text{microwave}}λinfrared​<λmicrowave​

    So, optical communication waves have shorter, not longer, wavelength than microwaves.

    Therefore, Assertion A is false.

  2. Analyze Reason R

    Reason R says:

    Infrared EM waves are more energetic than microwaves.

    Energy of a photon is: E=hν=hcλE = h\nu = \frac{hc}{\lambda}E=hν=λhc​

    Since infrared has higher frequency and shorter wavelength than microwaves, infrared photons have greater energy than microwave photons.

    Therefore, Reason R is true.

  3. Choose the correct option

    • Assertion A: False
    • Reason R: True

    Hence, the correct option is: D\boxed{\text{D}}D​

  4. Comparison with stored answer

    Stored correct answer: D

    My derived answer: D

    So, the answer agrees with the stored answer.

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