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If between wavelength $\lambda$ and $\lambda+d \lambda, e_\lambda$ and $a_\lambda$ be the emissive and absorptive powers of a body and $E_\lambda$ be the emissive power of a perfectly black body, then according to Kirchoff's law, which is true

• A
  $e_\lambda=a_\lambda=E_\lambda$
• B
  $e_\lambda E_\lambda=a_\lambda$
• ✓
  $e_\lambda=a_\lambda E_\lambda$
• D
  $e_\lambda a_\lambda E_\lambda=$ constant