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Redshift and Hubble's Law
Redshift is the observed shift of spectral features toward longer wavelengths. For distant galaxies, cosmological redshift is a key indicator of cosmic expansion. Hubble's law relates a galaxy's recession rate to its distance.
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Redshift and Hubble's Law
What is it?
Redshift is the observed shift of spectral features toward longer wavelengths. For distant galaxies, cosmological redshift is a key indicator of cosmic expansion. Hubble's law relates a galaxy's recession rate to its distance.
In simple words
- Galaxy redshift and Hubble's law provide key evidence for cosmic expansion.
Recommended for Class 12
Full school-level explanation
Redshift is the observed shift of spectral features toward longer wavelengths. For distant galaxies, cosmological redshift is a key indicator of cosmic expansion. Hubble's law relates a galaxy's recession rate to its distance.
Meaning
Redshift can be written: z = λobs − λemitλemit where: `λ_obs` = observed wavelength `λ_emit` = emitted/reference wavelength. For small redshifts, an approximate velocity relation is: v ≈ cz Hubble's law for nearby cosmological distances is: v = H₀d where: `v` = recession velocity/rate in the low-redshift approximation `d` = distance `H₀` = Hubble constant. If distance increases, recession rate generally increases. The relation provides strong observational evidence that cosmic distances between widely separated, gravitationally unbound galaxies increase over time.
Formula / Key Relation
z = Δλ/λemit v ≈ cz for sufficiently small `z` v = H₀d
Remember
- z = Δλ/λemit
- v ≈ cz
- v = H₀d
Deeper understanding
Go deeper on Redshift and Hubble's Law: connect the definition to reasons, relationships, exceptions, and exam wording.
Common mistakes
Exam focus
Redshift
Exam focus
Quick revision
- z = Δλ/λemit
- v ≈ cz
- v = H₀d
- Meaning: Redshift can be written: z = λobs − λemitλemit where: `λ_obs` = observed wavelength `λ
- Formula / Key Relation: z = Δλ/λemit v ≈ cz for sufficiently small `z` v = H₀d
- Galaxy redshift and Hubble's law provide key evidence for cosmic expansion.
For long answers on Redshift and Hubble's Law: define clearly → explain the main parts → give one example → state one exam caution.
Exam Focus
Exam Focus
Important points
- z = Δλ/λemit
- v ≈ cz
- v = H₀d
- Meaning: Redshift can be written: z = λobs − λemitλemit where: `λ_obs` = observed wavelength `λ
Important formulas
- z = Δλ/λemit
- v ≈ cz
- v = H₀d
Common exam traps
- Do not apply `v=cz` to arbitrarily large redshift.
- Do not interpret expansion as galaxies simply flying outward from one central point in ordinary pre-existing space.
Long question structure
Definition → key parts → example → exam caution
Common Mistakes
Common Mistakes
- Mistake
Do not apply `v=cz` to arbitrarily large redshift.
- Mistake
Do not interpret expansion as galaxies simply flying outward from one central point in ordinary pre-existing space.
- Mistake
Do not apply `v=cz` to arbitrarily large redshift.
Revision Zone
60-Second Revision
Quick cues from this topic — use them for last-minute revision.
z = Δλ/λemit
v ≈ cz
v = H₀d
Meaning: Redshift can be written: z = λobs − λemitλemit where: `λ_obs` = observed wavelength `λ
Redshift is the observed shift of spectral features toward longer wavelengths. For distant galaxies, cosmological redshift is a key indicator of cosmic exp
z = Δλ/λemit
- Definition
- Redshift is the observed shift of spectral features toward longer wavelengths. For distant galaxies, cosmological redshift is a key indicator of cosmic exp
- Formula
- z = Δλ/λemit
- Critical warning
- Do not apply `v=cz` to arbitrarily large redshift.
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Exam Practice
Define
Q1. Define Redshift and Hubble's Law.
Explain
Q2. Explain: Meaning.
Example
Q3. Give one clear example of Redshift and Hubble's Law and say why it fits.
Mistake
Q4. State one common mistake students make about Redshift and Hubble's Law.
Exam note
Q5. Write a short exam note on Redshift and Hubble's Law: definition, two points, one example.
Sources & References
School-standard facts for Matric and Intermediate. Original explanations — not copied from textbooks.