Topic 7&8: Radioactivity & Astrophysics

Question 1

Why does gravitational field strength differ in different planets?

Answer 1

It depends on the mass of the planet

Question 2

What type of forces causes stuff to orbit around something?

Answer 2

Gravitational force

Question 3

What are the differences in the orbits of comets, moons and planets

Answer 3

• Comets orbit elliptically
• Moons orbit circularly
• Planets orbit in a slightly squashed circle (ellipses)

Question 4

How do you calculate for the orbital speed?

Answer 4

2πr
Orbital speed = ———
T

Question 5

Rank the colours of the star by their temperatures

Answer 5

Hottest ————————————————————> Coldest

Blue, Blue White, Yellow, Orange, Red

Question 6

What is a nebula?

Answer 6

• A large cloud of dusts and gas particles drawn by gravitational force
• As particles get closer, the temperature and pressure becomes so large that it forms a star (nuclear fusion)

Question 7

What is a star (main sequence)?

Answer 7

• Caused by nuclear fusion
• A main sequence star is when particles are balanced and doesn’t pull inwards.
• Remains for millions of years

Question 8

What is a red giant?

Answer 8

• When a star runs out of hydrogen fuel, the gravitational force will push particles,especially inwards again
• Helium fusion will then happen and it expands into a bigger star
• As surface area is now larger, the temperature will be cooler

Question 9

What is a white dwarf?

Answer 9

• As helium fuel runs out again, the red giant will collapse inwards
• It heats ups so much that it turns white and becomes really small and dense as no fusion occurs

Question 10

How can a star evolute to have a bigger mass than the sun?

Answer 10

• A giant star forms into a red supergiant
• When it runs out of fuel, the it collapses and it explodes to form a Supernova

Question 11

What is an absolute magnitude?

Answer 11

A measure of how bright the star would be if it were seen from a standard distance

Question 12

What is a HR (Hertzsprung-Russel) diagram?

Answer 12

It shows the relationship between the luminosity and temperature of a star

Question 13

What were the scientists’ belief in the evolution of the Universe

Answer 13

• The universe was originally a tiny and dense place
• It then exploded and it has been expanding till now.
• The red-shift proves the expansion and the CMBR proves the energy of explosion

Question 14

Provide some evidence for the Big Bang Theory

Answer 14

Red-Shift:
- It is the stretching of a wave.
- Since the wave is stretching, that means that light is moving further away from us
- Which means that the universe is expanding

CMBR:
- The microwave radiation is something that would’ve been produced during the explosion
- Microwaves are stretched remains of high energy gamma radiations.
- They are stretched because the universe is expanding

Question 15

What are the relationship between change in wavelength, reference wavelength, velocity of a galaxy and speed of light?

Answer 15

Change in wavelength Velocity of a galaxy
——————————— = ————————————
Reference wavelength Speed of light

Question 16

Describe the red-shift in light received from galaxies at different distances away from the Earth

Answer 16

The further away a galaxy, the greater the red-shift will be.

Question 17

What are the three types of ionising radiation

Answer 17

• Alpha (α)
• Beta (β)
• Gamma (γ)

Question 18

Which ionising radiation is the strongest and which one is the weakest?

Answer 18

Strongest: Gamma

               Beta

Weakest: Alpha

Question 19

How can you investigate the penetration powers of different types of radiation

Answer 19

• Use a Geiger Muller tube
• Test the radiations with paper, aluminium and lead
• The count will significantly decrease if radiation is stopped

Question 20

What are the mass and atomic numbers for the three ionising radiation

Answer 20

4 0 0
α β γ
2 -1 0

Question 21

What is a photographic film for

Answer 21

The photographic film darkens the radiation to be able to detect for it

Question 22

What is the definition of half-life

Answer 22

The time taken for a radioactivity source to half its original value

Question 23

Describe how radioactivity is used in the medical industry

Answer 23

• Gamma radiography
• Medical tracer (MRI)
• Radiotherapy (Cancer treatments)
• Sterilisation

Question 24

What is the difference between contamination and irradiation

Answer 24

• Contamination is when radioactive atoms deposits on it
• Irradiation is when it is exposed to radiations

Question 25

What are the dangers of ionising radiations?

Answer 25

• They can cause mutations as it is very ionising
• They can damage cells and tissue
• Disposal of radioactive waste can cause harms

Question 26

What is nuclear fusion?

Answer 26

When two daughter nuclei join to form a bigger nucleus

Question 27

What is nuclear fission?

Answer 27

When a nucleus splits into two daughter nuclei and releasing three neutrons

Question 28

Describe the process of nuclear fission of Uranium 235?

Answer 28

• Uranium 235 absorbs a neutron to initiate fission
• As it turns into 236, it becomes unstable
• It then splits into 2 daughter nuclei and releasing three neutrons

Question 29

Describe the process of Uranium 235 fission

Answer 29

• Uranium 235 absorbs a neutron to initiate the fission
• As it is now 236, it turns unstable
• It then splits into 2 daughter nuclei and releases 3 neutrons

Question 30

What is chain reaction and how does it happen with Uranium 235

Answer 30

• A series of event that is caused by the previous one
• When Uranium 235 absorbs neutron to split into 2 daughter nuclei, it releases 3 neutrons
• These 3 neutrons go on and react with other Uranium causing unlimited fission to occur

Question 31

What does a moderator do in a nuclear reactor

Answer 31

It absorbs energy to slow down neutrons moving

Question 32

What does control rods do in a nuclear reactor

Answer 32

It absorbs neutrons to completely stop chain reaction going on

Question 33

What does a shielding do in a nuclear reactor

Answer 33

A really thick concrete and a steel reactor vessel that prevents radiation escaping