Unit 1 Exam Flashcards
(50 cards)
Wave - define
A wave is a transmission of energy through osscilations, from one location to another, without the net transferral of matter.
Difference between longtitudinal and transverse waves:
A longtitudinal wave is where movement of the material is parallel to energy flow - backwards and forwards motion. It includes sound waves and underwater movement. It can only be a mechanical wave.
A transverse wave is where oscillations take place 90 degrees to energy flow. It includes light waves and water waves. It can be either a mechanical or electromagnetic wave.
Difference between electromagnetic and mechanical waves.
Electromagnetic:
- Refers to the electromagnetic spectrum
- Waves travel without needing to oscillate a medium, through back and forth interaction between electric and magnetic fields.
- Always transverse
- Travels at 3.0 x 10 to the 8 metres per second
Mechanical:
- Require a material to travel through/matter to physically move
- Can be transverse or longtitudinal
Identify the key properties of waves
Frequency: The number of full cycles of waves which take place every second - measured in Hx, symbol is f
Period: The time it takes for a full cycle of waves to take place - measured in seconds, symbol is t
Wavelength: The distance between two identical points of two waves - measured in metres, symbol is lambda
Velocity: The rate of speed that the wave is travelling at - measured in metres per second, symbol is v
Speed + Wavelength + Frequency relationship
As velocity increases, frequency stays the same (as it relies upon the source of the wave / the medium it travels through). Therefore wavelength must also increase, to accomodate.
Relate how frequency and wavelength influence electromagnetic waves
- Speed of the wave is constant, at 3.0 x 10 to the power of 8 metres per second - v=3.0 x 10 ^ 8
- Therefore, as wavelength increases, frequency must decrease, and vice versa, to maintain this constant rate of speed.
- As frequency of the wave corresponds to its energy, where radio waves have long wavelengths and low frequencies, gamma radiation has the highest frequency and lowest wavelength.
Describe the uses of electromagnetic waves in society
Radio - Used for telecommunication purposes, including mobile phones, television and radio broadcasting. They are ideal for this, as they can travel long distances and pass through a variety of materials and conditions - stemming from their long wavelength.
Microwaves - Used for radar systems, heating food, and communication in satellite and mobile phone systems. This is due to their shorter wavelength, and ability to bounce around different objects.
Infrared - Transmit heat from the sun, involved in fires and radiators. This is due to how when infrared waves travel through the air, they collide and interact with the particles in a different materials, producing thermal energy.
Visible Light - This allows for humans to see different objects. It is the only portion of the electromagnetic spectrum that humans can perceive, and is also 40% of the radiation emitted by the sun.
Ultraviolet - Used for killing bacteria and stimulating production of Vitamin D in the skin. This is due to how it has relatively high levels of energy, that is not as dangerous as over-exposure to X and Gamma Rays.
X-Rays - Used for viewing inside of bodies and objects. This is due to its’ high penetration abilities, however, this can also result in damage to cells.
Gamma Rays - Used for medicine for killing cancer cells. This is due to its’ even higher penetration abilities, and thus, ability to kill targeted cells.
Explain the process of refraction and total internal reflection, and when it occurs
Refraction is how light enters a medium at an angle with a different refractive index, bending towards or away from the normal (lower index = away, more = towards). This bending takes place due to how part of a wavefront enters the medium first, changing speed, causing the rest of the wave to change direction to accomodate for that new speed.
Total internal reflection takes place when light is travelling into a medium with a lower refractive index, which means that the light refracts away from the normal. Therefore, the refracted ray will reach 90 degrees first, and can be trapped inside the material. The incident angle where the 90 degree angle exists, is the critical angle.
Explain the process of dispersion as the splitting of white light into separate colours
The speed of light depends on the material it is travelling through, and the light’s frequency. As white light is made up of a combination of all visible colours of the spectrum, once angled at a transperant wedge, the higher frequency purple light will move slower through the prism (corresponding to its’ shorter wavelength), refracting at a greater angle compared to the low frequency red light (corresponding to its’ longer wavelength). As this light exits the prism, the full range of colours will be visible, where dispersion has occurred.
Describe temperature with reference to the average kinetic energy of the atoms and molecules within a system
The Kinetic Theory of Matter states that all matter is comprised of small particles in constant random motion. More thermal energy corresponds to greater movement of particles, and when they collide, they do not transfer ‘heat,’ merely kinetic energy. Temperature is specifically the measure of average translational kinetic energy of particles (how fast the particles vibrate with this energy).
Distinguish between conduction, convection and radiation with reference to heat transfers within
and between systems
- Conduction: Mechanism of heat transferral that does not involve the movement of matter. Rather it is the movement of thermal energy through collisions of particles, within direct contact between 2 objects. Conductors (such as metals, due to delocalised electrons), transfer energy much more rapidly than Insulators.
- Convection: Mechanism of heat transferral where a region of a fluid is heated, resulting in an increase in the average translational kinetic energy of the particles belonging to that region of fluid. As they gain this energy, they spread out further part, and that region becomes less dense. The denser regions of the fluid above fall down under gravity, displacing the heated region up. This force of displacement is known as a convection current.
- Thermal radiation - Mechanism of heat transferral through waves of electromagnetic radiation, where particles collide resulting in acceleration of those particles’ charges, and subsequently, the emission of radiation (typically in the form of infrared). This radiation can be registered as heat.
Fire analogy…. - mechanisms of heat transferral
Thermal radiation:
- Particles within the flames and hot coals are moving at high speeds and colliding regularly. This can result in their charged parts accelerating, and emitting waves of infrared radiation, that travel through the air, and hit your skin. No contact is needed, and it can take place in empty space.
Conduction:
- Touching a metal fire poker involves the heat moving from the hotter object (the poker) to the colder object (your hand), through more energetic particles vibrating and transferring energy to neighbouring, less energetic particles. It requires physical contact, and is strong in metals.
Convection:
- The region of air directly above the fire is applied with heat, resulting in particles increasing in energy and spreading further apart. This results in a reduction in density, where the cooler, denser air above falls under gravity, displacing the hotter air up. This spreads the heat to individuals around the fire. It requires use of a fluid.
Specific Heat Capacity
The amount of joules of energy required to change the temperature of 1kg of a substance by 1 degree Celsius. Different materials store this energy in different ways, before translational kinetic energy is impacted.
Evaporation
Process on surface of liquids where the more energetic particles escape. This reduces overall average translational kinetic energy of remaining particles, and the temperature will drop. It involves a change in state from a liquid to a gas. The rate of evaporation increases with the overall temperature of the liquid, drier environment, and air moving over the liquid surface (helping particles escape).
Latent Heat
Known as ‘hidden heat’ where temperature does not change, even though thermal energy enters or leaves a substance. This energy is used to break down the substance’s bonds to change its’ state. Officially, it is defined as the ‘amount of energy required to change a unit mass of a substance from either a solid-liquid (latent heat of fusion) or liquid-gas (latent heat of vaporisation).’
Describe the fundamental forces in the nucleus
- The Gravitational Force - weak enough that the impact on the nucleus can be ignored
- Strong force - the strongest, most dominating of all the forces. It has a short range, operating across the width of a nucleus. It holds nucleons together and can be modelled as a spring - attractive unless close together
- Electrostatic Force - The second-strongest force, which determines if charges attract or repel. Like charges repel, whilst opposite attract. It is a force of repulsion for protons in the nucleus, with an infinite range.
- Weak force - Responsible for changes in nucleons, resulting in something emitted, such as an antineutrino. Its’ range is the width of a proton.
Explain what makes a nucleus stable
It depends on the balance of protons and neutrons.
If the Nucleus ≤ 20 nucleons - balance is required between protons and neutrons
If 21 ≤ N ≤ 83 nucleons - requires more neutrons compared to protons
If 83 + Nuclei - it is inherently unstable, and all isotopes of these elements are radioisotopes.
The electrostatic force has an infinite range, so over time, more neutrons are required to counteract the repulsive effects of the protons. However, as the strong force’s power is limited to a length of a specific nucleus, eventually the electrostatic force’s range is too great and will overpower the strong force.
Binding energy
Binding energy is the amount of energy required to pull apart two nucleons within a nucleus. The more energy required, the more stable the nucleus.
Describe the meaning of half life
The half life refers to the time it takes for 50% of a radioactive sample to decay into something more stable. An individual cannot predict individual outcomes, but they can use probabilities to map out what is expected to happen.
Short half life = Faster decay rate, higher instability
Long half life = Slower decay rate, lower instability
Alpha
Involves decay of the heaviest radioactive elements, where size must be reduced to increase stability. It emits 2 protons and 2 neutrons.
- Highly ionising (ability to break electron from an atom), due to its’ strong charge
- Inflicts high levels of damage in short spaces of time. It is relatively large so it often collides with matter, limiting its’ penetration abilities.
Beta Decay -
Beta Minus - Neutron in nucleus changes into a proton, emitting an electron and an antineutrino - used for excess neutrons in the nucleus,
Beta Plus - Proton changes into a neutron and positron, emitting a positron and neutrino - used for excess protons, with no need to change mass number
- moderate ionising power - smaller and less charge, so it interacts less with other materials
- medium penetrating ability, where electrons are significantly smaller than alpha particles, so they can avoid collissions for longer
Gamma Decay -
Has no mass or charge, emitting electromagnetic radiation due to excess energy in the nucleus, settling that nucleus down after a beta or alpha particle has been emitted
- low ionising power - it has no charge at all, so no change takes place in the daughter nucleus
- greatest penetration ability - it is mass-less and charge-less so it doesn’t interact with matter as strongly as charged material
Fusion:
- Combining 2 smaller nuclei into one larger nucleus
- Energy is released, as mass of the reactants is reduced with more binding energy required to hold the final product together
- This is currently impossible to replicate on earth, as electrostatic repulsion between the 2 charged objects must be overcome. It requires extremely high pressure and temperature environments, such as that found on the sun (pressure = pushing nuclei close together, temperature = more chance of collission).
Fission
- Dividing one larger nucleus into 2 smaller daughter products
- Energy is released as the original reactant requires more energy to be held together than the individual daughter products
- It is possible to replicate on earth, used as a controversial source of energy for power plants
