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Physics

The frequency of violet light is 7.5 x 1014 Hz. Its wavelength in nm is :

  1. 7500 nm
  2. 4000 nm
  3. 400 nm
  4. 750 nm

Spectrum

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Answer

400 nm

Reason — As we know,

Speed of light (c) = Frequency (f) x Wavelength (λ)

and

C = 3 x 108 m s-1

Frequency range = 7.5 × 1014 Hz

Substituting the values in the formula,

3×108=7.5×1014×λλ=3×1087.5×1014⇒λ=0.4×10−6m⇒λ=400×10−9m3 \times 10^8 = 7.5 × 10^{14} \times λ \\[0.5em] \text {λ} = \dfrac {3 \times 10^8 }{7.5 × 10^{14}} \\[0.5em] \Rightarrow \text {λ} = 0.4 \times 10^{-6} \text {m} \\[0.5em] \Rightarrow \text {λ} = 400 \times 10^{-9} \text {m} \\[0.5em]

Therefore,

λ = 400 nm

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