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Date May 2012 Marks available 3 Reference code 12M.3.HL.TZ2.3
Level Higher level Paper Paper 3 Time zone Time zone 2
Command term Determine Question number 3 Adapted from N/A

Question

This question is about Hubble’s law.

State Hubble’s law.

[1]
a.

Measured values of the Hubble constant can vary between 40 kms–1 Mpc–1 and 90 kms–1 Mpc–1. State the reason for this wide variation in values.

[1]
b.

The blue line in the spectrum of atomic hydrogen as measured in the laboratory is 490 nm. The same line in the spectrum of light from a galaxy has a wavelength of 500 nm.

Determine the distance of the galaxy from Earth. You may assume that the Hubble constant=70 km s–1 Mpc–1.

[3]
c.

Markscheme

the recessional speed of galaxies is proportional to their distance from Earth/us/each other / v = H0d (with terms defined);

a.

there is a large uncertainty in the measurement of galactic distances / it is difficult to accurately determine galactic distances;

b.

\(v = c\frac{{\Delta \lambda }}{\lambda }\);
\( = \left( {3 \times 10^8 \times \frac{{10}}{{490}} = } \right)6.1 \times {10^3}{\rm{km}}{{\rm{s}}^{ - 1}}\);
\(d = \frac{v}{H}\left( { = \frac{{6100}}{{70}}} \right) = 87{\rm{Mpc}}\);

c.

Examiners report

 

a.

 

b.

 

c.

Syllabus sections

Option D: Astrophysics » Option D: Astrophysics (Core topics) » D.3 – Cosmology
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