S2 Cosmology

Question 1

1. Explain what has to happen for the passage of time to be measured, giving an example

Answer 1

Something has to change for the passage of time to be measured

e.g. the apparent position of the sun in the sky.

Question 2

2. Explain what is meant by the “arrow of time”.

Answer 2

Time only moves forward, not backwards. This is because the universe naturally moves from a state of order to disorder and not the reverse.

Question 3

3. Define entropy, giving an example.

Answer 3

Entropy is a measure of disorder,

e.g. a sandcastle has low entropy because it is ordered; (less ways it could be arranged)

a pile of sand has high entropy because it is disordered. (lots of ways it could be arranged)

Question 4

4. How is the entropy of the universe changing over time?

Answer 4

The universe is moving from low entropy (order) to high entropy (disorder).

Question 5

5. State the approximate age of the universe.

Answer 5

The approximate age of the universe is 13.8 billion years.

Question 6

6. Perform calculations using scientific notation.

Example: What is 13.8 billion years in scientific notation?

Answer 6

13.8 billion years = 13,800,000,000 years = 1.38 x 10¹⁰ years

Question 7

6. Perform calculations using scientific notation.

Example: Convert 3.00 x 10⁸ m/s into normal notation.

Answer 7

3.00 x 10⁸ m/s = 300,000,000 m/s

Question 8

7. State the speed of light in m/s and its symbol.

Answer 8

The speed of light (c) is 3.00 x 10⁸ m/s (or 300,000,000 m/s)

Question 9

8. State what is important about the speed of light.

Answer 9

The speed of light is the greatest speed achievable in the universe.

Question 10

9. State what the symbols mean and what units are used for

v=d/t

or

d = vt

Answer 10

d - distance (m)

v - speed (m/s)

t - time (s)

Question 11

9. Example

At the 2008 Beijing Olympics, Usain Bolt ran 100m in 9.69 seconds. Calculate his average speed.

Answer 11

d = 100 m

t = 9.69 s

v = ?

v = d/t

= 100/9.69

v = 10.32 m/s

Question 12

9. Example

You run at a steady speed of 6 m/s for 5 minutes. How far did you go?

Answer 12

v = 6 m/s

t = 5 min = 5 x 60 = 300 s

d = ?

d = vt

= 6x300

d = 1,800 m

Question 13

9. Example

James send a bowling ball off at 8.81 m/s. The first pin is 18.29 m away.

How long does it take for the bowl to hit the pin?

Answer 13

v = 8.81 m/s

d = 18.29 m

t = ?

d = vt

18. 29 = 8.81xt
19. 81xt = 18.29

t = 18.29/8.81

t = 2.08 s

Question 14

9. Example (involving light)

Light takes 1.28 seconds to travel from the moon to the earth. How far away is the moon?

Answer 14

v = c = 3 x 10⁸ m/s

t = 1.28 s

d = ?

d = vt

= 3 x 10⁸ x 1.28

d = 3.84 x 10⁸ m

Question 15

9. Example (invloving light)

The sun is 1.5 x 10¹¹ m away.

How long does it take light to travel from the sun to the Earth?

Answer 15

v = c = 3 x 10⁸ m/s

d = 1.5 x 10¹¹ m

t = ?

d = vt

1.5 x 10¹¹ = 3 x 10⁸ x t

3 x 10⁸ x t = 1.5 x 10¹¹

t = 1.5 x 10¹¹/3 x 10⁸

t = 500 s

Question 16

10. Explain how viewing the stars is looking back in time.

Answer 16

The stars are so far away that light will take many years to reach us from them. This means the light we see now left the stars many years ago and we see what the stars looked like at that time.

Question 17

11. State what is meant by a light year.

Answer 17

A light year is the distance that light travels in one year.

Question 18

12. State what Monsignor Georges Lemaître is famous for.

Answer 18

Monsignor Georges Lemaître was the first to siggest that the universe is expanding.

Question 19

13. State what scientific discovery Edwin Hubble is famous for.

Answer 19

Edwin Hubble obtained experimental proof of the expanding universe.

Question 20

14. Describe what Hubble’s Law tells us.

Answer 20

Hubble’s Law tells us that the further away a galaxy, the faster its recessional speed (how fast it is moving away from us).

Question 21

15. Give a simple account of the Big Bang.

Answer 21

The Big Bang is the name given to the start of the universe, when the universe expanded rapidly from a single point.

Question 22

16. State what particles were first to form after the Big Bang.

Answer 22

The first particles to form after the Big bang were quarks.

Question 23

17. Name the six different types (flavours) of quark.

Answer 23

The six different types (flavours) of quark are Up, Down, Top, Bottom, Strange and Charm.

Question 24

18. State which three quarks combine to form a proton.

Answer 24

A proton consists of Up, Up, Down quarks.

Question 25

18. State which three quarks combine to form a neutron.

Answer 25

A neutron consists of Up, Down, Down quarks.

Question 26

19. State what is meant by the terms atom and nucleus.

Answer 26

An atom is the smallest building block of matter than can exhibit chemical properties.

The nucleus is the centre of the atom where protons and neutrons are found. The electrons orbit the nucleus.

Question 27

20. State what is meant by the term element.

Answer 27

An element only contains one type of atom.

Question 28

21&22. Use nuclear notation to represent elements.

Answer 28

A – atomic number which is a unique number for each element telling us how many protons there are in the nucleus. Unless an atom has been charged, the number of electrons will also be equal to this.
Z – mass number which tells us the combined number of protons and neutrons
X – element symbol.

Question 29

21&22. How many protons, neutrons and electrons are there in uncharged Carbon 14.

Answer 29

6 protons (from the atomic number)

6 electrons (equal to number of protons since uncharged)

8 neutrons (mass number - atomic number = 14 - 6 = 8)