Physics Exam Flashcards

Physics Flash

Describe Bohr’s Model of the Atom

Describe Bohr’s Model of the Atom

Nucleus is: 

• A region in the centre of the atom

• Small and dense

• Contains most of atom’s mass

• Consists of protons and neutrons

Electrons:  

• orbit the nucleus

• in levels called shells

What mass and charge does a proton have?

Mass: 1, Charge: +1

What mass and charge does a neutron have?

Mass: 1, Charge: 0

What mass and charge does a electron have?

Mass: 1/1836, Charge: -1

Define mass number

Number of Protons and Neutrons

Define atomic number

Number of protons in an atom

Define isotopes and their properties

Isotopes are:

• Atoms with the same number of protons but a different amount of neutrons

• Have the same chemical properties

• Different Physical Properties

Describe and explain chemical properties between isotopes

It’s the same between isotopes because of the same arrangement and number of electrons, resulting in same behavior in chemical reactions

Describe and explain physical properties between isotopes

It’s the different between isotopes because the atoms weight is heavier/lighter which affects properties such as melting point, boiling point, density and/or nucleus stability.

Define radiation

The particles or waves emitted by radioactive substances

Define transmutation

The process of changing one element to another or one isotope to another

Define radioactivity

The decomposition of unstable nuclei to form different, more stable nucleus. It is a natural and completely spontaneous.

Define nucleon

A particle that lies inside the nucleus of an atom, a proton or neutron.

Describe strong nuclear force

Force that holds protons and neutrons together inside the nucleon and it is so strong that it overcomes electrostatic force.

Electrostatic Force

An attractive and repulsive force between particles between particles and is caused due to their electric charge. Same charges repel and opposite charges attract.

How do nuclei become radioactive in terms of strong nuclear force and electrostatic force?

Nuclei become radioactive if a balance is not upheld between the number of protons and neutrons, disrupting the strong nuclear force and requiring emission of excess particles or energy in the form of radiation.

Describe the law of conservation of mass and energy

Energy and mass cannot be created nor destroyed but can be transformed between each other.

Define mass defect and how it is observed within an atom

The mass lost when separate nucleons bind to form a nucleus.

Define and Describe binding energy

The energy that must be supplied to split up a nucleus into consistent nucleons and is equivalent to the mass defect. It is also the energy released when nucleons bind to form a nucleus.

Explain why a mass defect must be present for a nucleus to stay stable

Mass defect is equivalent to the absence of binding energy and the absence of binding energy. Low energy means stability because the lower the energy, the more energy that must be added to disturb the nucleus and induce reactions, making it more difficult to split apart.

Explain why you need a large amount of energy to break apart a nucleus

To make up for the mass defect formed when the nucleus is formed, energy is transformed into mass, allowing constituent nucleons to separate.

Explain why the formation of nuclei releases energy

When protons and neutrons join together, energy is released because a part of the nucleons’ mass is converted to energy, which released as binding energy

Describe Einstein’s equation regarding mass defect and binding energy

Relates energy to mass, therefore relating binding energy and mass defect. Without movement, calculates for the binding energy

What is Einstien’s equation?

E = mc²

E – energy measured in joules  
m – mass measured in kilograms  
c – speed of light (3 * 10^8 m/s)

Why is the energy released in nuclear reactions?

The binding energy of products is greater than the binder energy of reactants, meaning that the different in binding energy is released as part of the energy consumed to induce the reaction.

Explain why nuclei with a large binding energy per nucleon are most stable?

Having a large binding energy means more energy is needed to make up for the mass defect. Making up for the mass defect is required to induce reactions, thus making reactions harder and making the nucleus more stable.

What is ionizing radiation?

The release of energy that allows an unstable nucleus to attain a more stable form. Enough energy to break an electron away from an atom.

Define Alpha Radiation in terms of emitted radiation, charge, energy, mass, velocity, ionizing power, deflection in electric fields, deflection in magnetic fields, penetration in air, penetration in matter and how it is stopped.

Emitted Radiation: Alpha particles (2 protons and 2 neutrons)

Charge: +2

Energy: High Energy ~6 MeV

Mass: 4

Velocity: Low, ~0.06c

Ionizing Power: Strongly ionizing, will “steal” ions from the first thing from the first thing it contacts.

Deflection in electric fields: Weakly deflected towards negative plate/from positive plate

Deflection in magnetic fields: Weakly deflected towards negative plate

Penetration in air: Only a few cm (picks up electrons and becomes a helium atom)

Path through matter: Straight line path

Stopped by: Paper, clothes, fabric, skin

Define Beta Radiation in terms of emitted radiation, charge, energy, mass, velocity, ionizing power, deflection in electric fields, deflection in magnetic fields, penetration in air, penetration in matter and how it is stopped.

Emitted Radiation: High energy electrons emitted from when a neutron decays into a proton and an electron

Charge: -1

Energy: ~1 MeV

Mass: ~1/1836

Velocity: Up to ~0.98c

Ionizing Power: Weakly Ionizing

Deflection in electric fields: Strongly deflected from negative plate

Deflection in magnetic fields: Strongly deflected from negative plate

Penetration in air: Travels several meters in air

Path through matter: Tortuous path through matter

Stopped by: mms of aluminum, lead

Define Gamma Radiation in terms of emitted radiation, charge, energy, mass, velocity, ionizing power, deflection in electric fields, deflection in magnetic fields, penetration in air, penetration in matter and how it is stopped.

Emitted Radiation: High energy electromagnetic waves

Charge: 0

Energy: Low energy ~0.1 MeV

Mass: 0

Velocity: 1c

Ionizing Power: Very Weakly Ionizing

Deflection in electric fields: Not deflected

Deflection in magnetic fields: Not deflected

Penetration in air: Kilometers

Path through matter: Straight line path decreasing density the further it travels from the source

Stopped by: Several centimeters of lead and meters of concrete

Outline the risks of radiation exposure

• Radiation Sickness

• Radiation Burns

• Damage to internal organs

• Damage to tissue due to ionizations

• Damaging DNA, increasing cancer risk

Define half-life

The time taken for the number of radioactive nuclei/amount of radioactivity in a sample to halve through decay

Define activity

Overall rate of decay of all isotopes in a radioactive sample

Define count

1 radioactive decay measured in becquerels (Bq) - one decay/count per second

Describe the relationship between activity and number of radioactive isotopes

Directly correlated as the number of radioactive isotopes decreases, the number of atoms that produce radiation decreases, leading to a decrease in radiation overall, decreasing activity.

Describe 3 ways to quantify half-life

• Time for half of the mass of substance to decay

• Time for % of radioactive isotope within a mixture to halve

• Time for the activity (counts per second) to halve

Describe the process of carbon-dating

Carbon 14 is a radioactive isotope formed in the atmosphere by action of cosmic rays on nitrogen 14. CO₂ containing C-14 is absorbed by plants during photosynthesis. C-14 is passed on to animals that consume the plants through comparing the proportion of C-14 of a dead object to the proportion present in living material and using C-14’s decay curve given half life is 5730 years amount of time since death of an object can be estimated.

Describe 3 problems with carbon dating

• If the sample is over 60000 years old, there is not enough C-14 to measure accurately.

• Samples may be contaminated, confusing readings

• May be imprecise for items from the 1940s, as nuclear bombs, reactors and open air tests increased the proportion of C-14 in the atmosphere

Define decay chain

A process in which many radioactive isotopes decay to form a nucleus that is also radioactive, continuing decay until a stable state is reached.

Define fission and describe its characteristics.

Splitting of heavier nucleus into smaller, light nuclei. Can be spontaneous and completely random and can be induced neutron capture. Releases large amounts of energy, often involving release of gamma radiation and free neutrons.

Define fusion and describe its characteristics.

Joining of two nuclei to form one heavier nucleus releasing a massive amount of energy. This usually releases protons or neutrons, as well as new nucleus but requires a huge amount of energy in the form of heat and pressure to overcome the electrostatic repulsion of protons in nuclei.

Compare nuclear fusion and fission, relating 3 differences and 3 similarities.

differences in: 
- fusion is merging of light atomic nuclei, fission is splitting of heavy atomic nucleus  
- fusion is light nuclei, fission is heavy nucleus  
- more energy is released in fusion  
- fusion requires more extreme high temperatures and pressures than fission  
- fusion produces minimal radioactive waste in the form of short lived isotopes, while fission produces long living radioactive waste requiring careful management  
- fusion is experimental, fission is established for energy generation  
- fusion has a low risk of accidents, while the risks of fission include accidents and nuclear proliferation  
 
similarities in:

- Both lead to a new nucleus being produced 

- Both release energy  

- Both may have radioactive side products and emission of radiation  

- Both require extreme conditions (though lesser in fusion)

Define chain reactions

The process in which a fission reaction releases several neutrons, inducing another fission reaction which continue the process, forming a positive feedback loop that leads to a series of fission reactions.

Outline 2 applications of chain reactions

• Nuclear bombs – induce a large amount of fission reactions to release a large amount of energy, causing an explosion through an uncontrolled chain reaction
  

• Nuclear power plants – convert heat energy from controlled chain reactions to electricity

Define critical mass

The minimum amount of radioactive isotope required to sustain a chain reaction or else the reaction will stop as it will run out of fuel

Describe induced nuclear fission

A more stable isotope is struck by a neutron. The isotope absorbing the neutron and becoming unstable, inducing fission as the nucleus splits to reach stability.

Define neutron capture

A neutron binds to a nucleus for a very brief moment of time causing the nucleus to split to become unstable and undergo fission

Describe an uncontrolled chain reaction

Neutrons are released too quickly, leading to many fission reactions occurring at once to maintain a chain reaction, releasing a very large amount of nuclear energy instantaneously/in the form of an explosion

Describe a controlled chain reaction

A chain reaction whose rate of reaction is controlled through absorption which controls the rate at which energy is released. This allows fission to occur in a self-generating manner and limits the amount of energy produced to a sufficient but safe level.

Contrast controlled and uncontrolled chain reactions

any 3 of the following:
- controlled reactions have a regulated and steady reaction rate, while uncontrolled reactions have a reaction rate that increases rapidly and uncontrollably  
- controlled reactions are relatively safe and typically have safety systems, while uncontrolled reactions are incredibly dangerous  
- controlled reactions have a steady and manageable energy output, while uncontrolled reactions have an instantaneous and explosive release of energy  
- the waste of controlled reactions is typically managed and contained, while uncontrolled reactions produce large amounts of radioactive material without management  

Compare controlled and uncontrolled chain reactions

any 3 of the following: 
- both release energy  
- both have the same radioactive by-products  
- both utilise nuclear fission  
- both depend on critical mass  

What does the reactor vessel consist of and function as?

Consists of:

• Concrete and metal

Function:

• Encases and prevents radiation from escaping from the reactor core

What do the fuel rods consist of and function as?

Consists of:

• Specific isotopes

Function:

• Nuclear fission is induced to produce controlled chain reactions

What do the control rods consist of and function as?

Consists of:

• Neutron absorbing substances e.g. boron

Function:

• Control the rate of reaction by absorbing neutrons

What does the moderator consist of and function as?

Consists of:

• Graphite or heavy water

Function:

• Slows down neutrons to allow for neutron capture, which won’t occur if the neutron is moving too fast

What does the steam generator consist of and function as?

Consists of:

• Turbine, heat exchanger, generator

Function:

• Functions to convert the heat of steam to kinetic energy to electricity that can be supplied commercially

Describe a nuclear reactor

A device in which nuclear reactions are generated and the chain reaction is controlled to release large amounts of steady heat, which is transformed into electricity.

Describe, in simple terms, how a nuclear reactor generates electricity.

In fuel rods of consisting of radioactive fuel, neutron induced fission is generated. This fission leads to a controlled chain reaction within the fuel rods producing a large but controlled amount of energy in the form of heat over a steady period of time. The fuel rods are suspended in a liquid called coolant which absorbs the heat and travels in a closed loop to a heat exchanger within the heat exchanger, heat is transferred from the coolant to water, converting the water to steam which travels to a turbine, causing it to spin. The turbine connected is connected to a generator which converts the energy of turbine’s movement to electricity which can be used and supplied commercially. Water is then cooled in a cooling tower, and the loops continue until the fuel rods run out of fuel.

Describe 3 advantages of using nuclear energy to generate electricity.

any 3 of the following:  
- very efficient with large amount of energy generated  
- no CO2 emissions  
- abundant fuel supply  
- high energy density of fuel  
- not affected by weather or environmental conditions  
- waste is strictly regulated (unlike fossil fuels) 
- requires less land

Describe 3 disadvantages of using nuclear energy to generate electricity.

any 3 of the following:  

• Nuclear weapon proliferation, allows nuclear weapons to be produced using nuclear reactor technology  

• Nuclear waste is very dangerous, hard to store, and radioactiv3  

• Accidents and disasters may occur, both of which have very detrimental environmental effects and are harmful and lethal to humans 

• High construction and initial costs 

• Mining fuel can be detrimental to the environment  

• Safety decommissioning old plants is very expensive and complex, requiring long term planning and resources

Describe the relationship between binding energy on radioactive decay.

The lower the binding energy per nucleon, the more unstable and prone to decay a nucleus is. This is because it is easy to induce decay as little energy is needed to make up for the binding energy.

Define electromagnetic force

An interaction that occurs between particles with electric charge via electromagnetic fields.

Give 3 reasons why alpha particles are highly ionizing.

1. Double positive charge  
2. Large mass  
3. Relatively slow