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25. Astronomy and cosmology
A section of Physics, 9702
Listing 10 of 19 questions
Define the radian. A telescope gives a clear view of a distant object when the angular displacement between the edges of the object is at least 9.7 × 10−6 rad. The Moon is approximately 3.8 × 105 km from Earth. Estimate the minimum diameter of a circular crater on the Moon’s surface that can be seen using the telescope. diameter = km Suggest why craters of the same diameter as that calculated in but on the surface of Mars are not visible using this telescope.
9702_s14_qp_42
THEORY
2014
Paper 4, Variant 2
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State Wien’s displacement law. shows the wavelength distributions of electromagnetic radiation emitted by two stars A and B. rate of emission 0.5 1.0 1.5 wavelength / μm 2.0 star A star B The surface temperature of star A is known to be 5800 K. Determine the surface temperature of star B. surface temperature = K Star B appears less bright than star A when viewed from the Earth. Use to suggest, with a reason, how else the physical appearance of star B compares with that of star A. The lines in have been corrected for redshift. State what is meant by redshift. Explain how cosmologists are able to determine that light from a distant star has undergone redshift.
9702_s22_qp_41
THEORY
2022
Paper 4, Variant 1
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State Wien’s displacement law. shows the wavelength distributions of electromagnetic radiation emitted by two stars A and B. rate of emission 0.5 1.0 1.5 wavelength / μm 2.0 star A star B The surface temperature of star A is known to be 5800 K. Determine the surface temperature of star B. surface temperature = K Star B appears less bright than star A when viewed from the Earth. Use to suggest, with a reason, how else the physical appearance of star B compares with that of star A. The lines in have been corrected for redshift. State what is meant by redshift. Explain how cosmologists are able to determine that light from a distant star has undergone redshift.
9702_s22_qp_43
THEORY
2022
Paper 4, Variant 3
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State Wien’s displacement law. Identify any symbols that you use. A cosmology student observes the electromagnetic radiation received from a star in a galaxy. The student uses Wien’s law to estimate the surface temperature of the star, a standard candle to estimate the distance to the galaxy, and the Stefan–Boltzmann law to estimate the radius of the star. The student observes that the radiation from the star is redshifted. State what is meant by a standard candle. State the reason why the radiation from the star is redshifted. The true values of the quantities observed or estimated are those that are corrected to allow for redshift. However, the student does not correct for redshift. By placing one tick (3) in each row, complete Table 10.1 to indicate how the observations and estimates made by the student compare with the true values. Table 10.1 student’s uncorrected value too low the same too high wavelength of radiation surface temperature of star distance to star radius of star
9702_w23_qp_42
THEORY
2023
Paper 4, Variant 2
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Explain how redshift leads to the idea that the Universe is expanding. Stars in a distant galaxy emit radiation. The total luminosity of the stars in the galaxy is 1.90 × 1036 W. The emission spectrum of the radiation contains a line X at a wavelength of 658 nm. Radiation from the galaxy is observed on the Earth. The observed radiation has a radiant flux intensity of 8.42 × 10–16 W m–2. In the observed emission spectrum, line X is at a wavelength of 726 nm. Determine: the distance d of the galaxy from the Earth d = m the speed v of the galaxy relative to the Earth. v = m s–1 Observations of many galaxies, such as the one in , lead to many pairs of values of d and v. Plotting these values reveals a trend. On , sketch the variation of v with d. d v State the name of the quantity represented by the gradient of the line in .
9702_w24_qp_41
THEORY
2024
Paper 4, Variant 1
View
Explain how redshift leads to the idea that the Universe is expanding. Stars in a distant galaxy emit radiation. The total luminosity of the stars in the galaxy is 1.90 × 1036 W. The emission spectrum of the radiation contains a line X at a wavelength of 658 nm. Radiation from the galaxy is observed on the Earth. The observed radiation has a radiant flux intensity of 8.42 × 10–16 W m–2. In the observed emission spectrum, line X is at a wavelength of 726 nm. Determine: the distance d of the galaxy from the Earth d = m the speed v of the galaxy relative to the Earth. v = m s–1 Observations of many galaxies, such as the one in , lead to many pairs of values of d and v. Plotting these values reveals a trend. On , sketch the variation of v with d. d v State the name of the quantity represented by the gradient of the line in .
9702_w24_qp_43
THEORY
2024
Paper 4, Variant 3
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shows part of the emission spectrum of visible radiation emitted by hydrogen gas in a star in a distant galaxy. increasing frequency The galaxy is moving away from the Earth at a speed of 6.2 × 106 m s–1. Explain how the positions of the lines in the emission spectrum seen by an observer on the Earth differ from the positions shown in . On , draw the three lines in possible positions in the spectrum seen by the observer. The lines in correspond to electron transitions down to the energy level –3.40 eV. One of the lines represents emitted radiation of wavelength 488 nm. Calculate the energy of a photon of this radiation. photon energy = J Determine the energy, in eV, of the energy level from which the electron transition originates to cause the emission of this radiation. energy level = eV Determine the wavelength, in nm, of this radiation as detected by the observer on the Earth. wavelength = nm A value for the Hubble constant is 2.3 × 10–18 s–1. Determine the distance of the galaxy from the Earth. distance = m ,  ,
9702_s24_qp_42
THEORY
2024
Paper 4, Variant 2
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shows the visible part of the emission spectrum from hydrogen gas in a laboratory on the Earth. The numbers indicate the wavelength, in nm, represented by each line. Explain how the emission spectrum provides evidence for the existence of discrete energy levels for the electron in a hydrogen atom. shows five of the energy levels in the hydrogen atom. The wavelengths of radiation shown in relate to transitions to the – 3.400 eV level in . energy – 0.378 eV – 0.544 eV – 0.850 eV X – 3.400 eV (not to scale) Show that the energy level X is –1.51 eV. The same part of the emission spectrum from hydrogen as in , observed in light from stars in a distant galaxy, is shown in . The numbers indicate the wavelengths in nm. The spectrum shows the same pattern as but with different wavelengths. State the name of the phenomenon that gives rise to the change in the wavelengths. State what this phenomenon shows about the motion of the galaxy. Use one of the lines in , and the corresponding line in , to determine the speed of the distant galaxy relative to the observer. speed = m s–1 The galaxy in is known to be a distance of 5.7 × 1024 m from the Earth. Use your answer in to determine a value for the Hubble constant H0. H0 = s–1
9702_w22_qp_42
THEORY
2022
Paper 4, Variant 2
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Questions Discovered
19