iGCSE Physics (0625) 6.2.3 The Universe-Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Detailed solution:
Redshift occurs when the light from an object receding from the observer is stretched.
This stretching results in an increase in the observed wavelength $\lambda$ of the electromagnetic radiation.
Option A is incorrect because light from galaxies moving towards Earth would be blueshifted (decreased $\lambda$).
Option C is incorrect as the Big Bang Theory describes the expansion of the Universe itself, not just the Solar System.
Option D is factually incorrect regarding the timeline and rate of expansion to the current size.
Therefore, statement B is the only scientifically accurate definition of redshift provided.
▶️ Answer/Explanation
Detailed solution:
Redshift occurs when the observed wavelength λ obs of light is greater than the emitted wavelength λ emit .
This increase in wavelength indicates that the source of light is moving away from the observer.
Astronomers observe that light from nearly all distant galaxies is redshifted, meaning their recession speed v is positive.
Since the redshift increases with distance d, it follows the Hubble Law v=H 0 d.
This universal recession provides strong evidence that the Universe is expanding.
Therefore, the logical conclusion is that galaxies are all moving away from each other.
▶️ Answer/Explanation
Detailed solution:
Redshift occurs when light from an object moving away from the observer is stretched.
In the visible spectrum, red light has the longest wavelength, so a shift toward red signifies an increase in $\lambda$.
Since the speed of light $c$ is constant in a vacuum ($3.0 \times 10^{8} m/s$), the wave equation $c = f\lambda$ applies.
As the wavelength $\lambda$ increases, the frequency $f$ must decrease to keep the speed constant.
Therefore, redshift is explicitly defined by an increase in the observed wavelength of the electromagnetic radiation.
This phenomenon provides critical evidence that distant galaxies are receding and that the Universe is expanding.