Worksheet 3: Dark Matter Concept Questions
Worksheet 3: Dark Matter Concept Questions
For each of the following questions, select the best answer and provide a brief explanation.
1) Physicists can calculate the mass of the Sun using their measurements of the radius of
a) the Sun and the Sun’s speed b) the Sun’s orbit and the Sun’s speed
c) a planet and the planet’s speed d) a planet’s orbit and the planet’s speed
2) The light from a star can tell physicists about its speed. The light from a really fast star will be
a) brighter b) fainter c) redder d) redder or bluer
3) The mass of galaxies can be determined by the orbital method and the brightness method. When both methods are used physicists found that the measurements disagreed
a) slightly and the orbital method gave a higher mass
b) slightly and the brightness method gave a higher mass
c) enormously and the orbital method gave a higher mass
d) enormously and the brightness method gave a higher mass
4) In which galaxies has dark matter has been detected?
a) Triangulum b) Andromeda c) Triangulum and Andromeda d) all galaxies tested
5) Dark matter can also be detected by the way it bends light. The mass calculated using this gravitational lensing method has discovered lots of dark matter in
a) our solar system b) our galaxy c) clusters of galaxies d) all three places
6) The mass found by gravitational lensing agrees with the amount of mass found by
a) orbital method b) brightness method c) both methods d) neither method
7) Dark matter could be made of astronomical objects that we know about but which are hard to see. However, the missing matter can`t be made of
a) planets, because each solar system would have to have thousands of huge planets
b) black holes and brown dwarfs because we should be able to detect them by gravitational lensing
c) black holes because we should be able to detect the materials they spray out when forming
d) all of the above
8) Physicists are trying to detect dark matter directly. They think it is made of
a) protons, neutrons and electrons b) WIMPS
c) WIMPS and/or axions d) protons, neutrons, electrons, WIMPS and axions
9) Most of the experiments to detect dark matter directly take place underground in order to block out
a) cosmic rays b) radioactivity c) sunlight d) noise
10) At present physicists
a) know what dark matter is except for a few small details
b) have some ideas of what dark matter might be and are testing these in debates
c) have some ideas of what dark matter might be and are testing these with experiments
Answers and notes for teachers
They questions are supposed to provide an opportunity for students to deepen what they have learnt from the video through discussions. Booklets of large font letters can help this process. You ask them to show you their choice - so you can assess their understanding - and then have turn and find someone with a different letter and explain their reasoning to each other.
1) d) radius of a planet’s orbit and the planet’s speed
You might want to have them draw labeled diagrams to explain their answers.
2) d) redder (if moving away) or bluer (if moving toward)
Many students may choose just redder because almost all galaxies are red-shifted because of the expansion of the universe. However, this light will be shifted on one side to be more red and on the other side to be less red because of the orbital motion.
3) c) enormously and the orbital method gave a higher mass
The two techniques are very well established and they give very different answers.
4) d) all galaxies tested
The video talks specifically about two galaxies, but many more have been tested and all of these show this missing mass.
5) c) clusters of galaxies
Lensing has been used within our galaxy to look for smaller concentrated masses like brown dwarfs and black holes. The dark matter in our galaxy is too diffuse to be detected by this technique.
6) a) orbital method
Two very different lines of evidence – lensing and orbital motion – are telling us that there is a lot of missing matter. They say that there is six times more dark matter than ordinary matter.
7) d) all of the above
Physicists first checked to see if the missing matter was just ordinary matter that is hard to see. These possibilities have been ruled out.
8) c) WIMPS and/or axions
Physicists have evidence that dark matter cannot be ordinary matter like protons, neutrons and electrons.
9) a) cosmic rays
Cosmic rays are very high energy particles bombarding the Earth whose origins are not well understood. They can trigger the dark matter detectors so a couple of kilometres of rock is needed to block them. Radioactivity from the surrounding rock can also affect the detectors and other shielding is needed for that and the rooms must be kept extremely clean to keep radioactive dust out.
10) c) have some ideas of what dark matter might be and are testing these with experiments