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Universe — Physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 SciencePhysicsUniverse1 Mark
MCQ
A particular emission line, detected in the light from a galaxy, has a wavelength $\lambda ' = 1.1\lambda $, where $\lambda $ is the proper wavelength of the line. The galaxy distance from us
  • ✓
    $1.6 \times {10^9}ly$
  • B
    $0.97 \times {10^9}ly$
  • C
    $2.4 \times {10^9}ly$
  • D
    $1.62 \times {10^{11}}ly$
✓

Answer

Correct option: A.
$1.6 \times {10^9}ly$
a
(a) From Hubble’s law $v = Hr$ where $H = $Hubble’s constant $= 19.3 mm/sec-ly$ and $ r = $

Distance of Galaxy from us.

According to Doppler’s effect speed of Galaxy $v = \frac{{c\Delta \lambda }}{\lambda }$

==> $r = \frac{{c\Delta \lambda }}{{H\lambda }} = \frac{{c \times 0.1\lambda }}{{H\lambda }} = \frac{{0.1\, \times 3 \times {{10}^8}}}{{19.3 \times 3 \times {{10}^{ - 3}}}} = 1.6 \times {10^9}\,ly$

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