AP EAPCET 21 May 2025 Shift 2 Paper

Given data
Wavelength emitted by the star (rest wavelength):
λ0=6600Å
Observed redshift (increase in wavelength):
∆λ=22Å
The redshift implies that the star is moving away from the Earth.
Formula (for non-relativistic Doppler shift)
For light at non-relativistic speeds:
‌

∆λ

λ0

=‌

v

c

where
v= radial speed of the source relative to the observer,
c=3×108ms−1.
Substituting values
‌‌

22

6600

=‌

v

3×108

‌v=3×108×‌

22

6600

‌v=3×108×3.33×10−3
‌v=1.0×106ms−1
‌v=106ms−1=10×105ms−1
Direction
Since the wavelength is red shifted, the star is receding from Earth.
Answer:
Option B
Receding away from Earth with a speed of 10×105m∕s