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# physics rev

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Dakota howells

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[Front]

whats a transverse wave
[Back]

a wave that oscillates perpendicular to its propagation

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### Questions:

94 questions
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 Whats a transverse wave A wave that oscillates perpendicular to its propagation
 Whats a longitudinal wave The vibrations are parallel to the direction of wave travel
 Black materials... Better emitters and absorbers / emit faster
 Doppler effect Where there is a change in frequency and wavelength
 Em spectrum (longest wavelength first) Radio, microwave, infrared, visible, uv, X-ray, guns
 What is refraction The change in direction of a wave at such a boundary. bend.
 Whats reflection Hen a wave hits boundary between two media where the wave speeds differ, but the wave stays in the original medium instead of passing into the second medium.
 What is diffraction He spreading out of waves when they go through a gap, or past the edge of a barrier.
 Whats the refractive index A measure of the change in the speed of light as it passes from a vacuum (or air as an approximation) into the material.
 How does sound travel thru air The air particles vibrate and collide with each other, causing the vibrations to pass between air particles.
 Critical angle The angle of incidence when the angle of refraction is 90 o, and the ray changes from just refracting to total internal reflection,
 Whats the frequency of human hearing 20 - 20,000 Hz
 What is total internal reflection (TIR)? When light travels through a medium and hits the solid-air boundary at an incident angle greater than the critical angle and is therefore reflected back into the solid as opposed to refracting out the other side
 What uses are there for total internal reflection? Endoscopes, optical fibres, etc.
 Evolution of stars bigger than sun Stellar nebula, protostar, main sequence, red super giant, supernova, black hole/neutron star
 Evolution same size as sun Steller nebula, protostar, main sequence, red giant, planetary nebula, white dwarf, black dwarf
 Whats red shift Redshift is a 'shift' of light waves traveling away from Earth.
 Whats the coolest star Red
 Whats the hottest star Blue
 What is absolute magnitude The luminosity of a star as if it was measured at a point which is a standard distance from the Earth
 What is magnitude How bright it is compared to the sun
 What are the standard units of mass, distance, velocity, acceleration, force, time, gravitational field strength, moments, and momentum Mass: kg, distance: m, velocity: m/s, acceleration: m/s², force: N, time: s, GFS: N/kg, moment: Nm, momentum: kg m/s
 Distance time graphs and average speed Gradient = speed (distance/time), average speed = total distance/total time, acceleration curves graph
 Velocity time graphs and acceleration Gradient = acceleration (velocity/time), area under graph = distance, horizontal line = constant velocity
 Speed equations V²=u²+2as, a=(v-u)/t, s=
 Effects of forces Changes in: speed, shape, and direction
 Types of forces Gravitational, electrostatic, thrust, upthrust, air resistance, compression, tension, and reaction
 How do vector quantities differ from scalar? Vector quantities have both direction *and* magnitude, while scalar quantities only have magnitude (e.g. velocity vs speed)
 Examples of vector quantities Forces, velocity, acceleration, displacement, weight
 Examples of scalar quantities Speed, energy, density, power, mass
 Resultant forces One force to rule them all... cancel out vertical/horizontal forces until you see the overall direction and magnitude affecting the object
 Friction Opposes motion
 Newton's second law F=ma
 Weight, mass, gravitational field strength W=mg
 Stopping distance Thinking distance (dependent on intoxication, tiredness, distractions, speed) + braking distance (dependent on road conditions, brake pad conditions, weather, vehicle mass, speed)
 Falling objects' forces Gravity vs air resistance, when equal the object is travelling at terminal velocity
 Hooke's law Extension of an elastic object is directly proportional to the force applied, up to the limit of proportionality
 Elasticity The ability of a material to recover its original shape after being deformed
 Momentum equation and conservation P=mv, total momentum of all objects prior to collision = total momentum of all objects post collision, therefore mv=mv can be used to calculate masses or velocities in a system.
 Momentum and safety Car safety features exist to slow the transfer of momentum, as a lower deceleration is less damaging than a rapid one. Seat belts have a bit of stretch so you still stop against the seat instead of the window, but you can go a little bit forward.“Speed has never killed anyone. Suddenly becoming stationary, that's what gets you.” ― Jeremy Clarkson
 Force, change in momentum, time taken Force = change in momentum/time taken, F=(mv-mu)/t
 Newton's third law Every action has an equal and opposite reaction
 Moment equation Moment = force x perpendicular distance from pivot
 Where does weight act? Centre of gravity
 How do you figure out the moments at either end of a beam with a mass somewhere along it? Measure distances, use moment=Fd to calculate moments at both ends
 Most ionising? Alpha
 Whats half life The time it takes for half of the unstable nuclei in a sample to decay or for the activity of the sample to halve or for the count rate to halve.
 Whats contamination Occurs when an object is exposed to a source of radiation outside the object
 What is fission? The splitting of a large atomic nucleus into smaller nuclei.
 What is fusion When two small, light nuclei join together to make one heavier nucleus
 Fission in a reactor In a nuclear reactor, a neutron is absorbed into a nucleus (typically uranium-235). This causes the nucleus to become uranium-236, which is violently unstable. The entire nucleus splits into two large fragments called 'daughter nuclei'. In addition to the 'daughter' products, two or three neutrons also explode out of the fission reaction and these can collide with other uranium nuclei to cause further fission reactions. This is known as a chain reaction. The fast moving neutrons carry most of the energy from the reaction with them (99%) but before the neutrons can collide with fresh uranium nuclei, they need to be slowed down. This is so that the energy can pass on to other components in the nuclear reactor, which is used to heat water to drive the turbines that turn the generators.
 Whats a control rod Stop neutrons from travelling between fuel rods and therefore change the speed of the chain reaction- boron
 What is a fuel rod So that the neutrons released will fly out and cause nuclear fission in other rods. - uranium
 Moderator Control the rate of reaction in the core of the nuclear reactor. - graphite
 Why high temp for fusion In order to force the nuclei together and overcome this electrostatic repulsion.
 What's a Becquerel? Unit of radioactivity, 1 nuclear decay / second
 How do you detect radiation? Photographic film or Geiger-Müller tube
 Why is radiation dangerous to health? Radiation can either kill cells outright or cause mutations leading to misbehaving cells and cancer. This doesn't just come from direct exposure to a nuclear facility but also from waste so proper disposal is vitally important.
 What is charge A property of a body which experiences a force in an electric field.
 What is current The rate of flow of charge
 What is ac The direction of the flow of electrons switches back and forth at regular intervals or cycles
 Dc A direct current flows in only one direction
 Why is ac used for transformers A transformer needs an alternating current that will create a changing magnetic field. A changing magnetic field also induces a changing voltage in a coil.
 As resistance increases... As resistance increases the current decreases.
 As voltage increases Current increases
 Energy stores Chem, kin, grav, elastic, thermal, magnet, electrostatic, nuc
 Energy transfers Mechan, eles, heating, radiation
 Whats conduction When heat moves from one object to another object through direct touch.
 Whats convection When particles with a lot of heat energy in a liquid or gas move and take the place of particles with less heat energy
 Radiation Transfer of heat via infra red waves,
 What is power The rate at which this energy is transferred
 Work done The amount of force needed to move an object a certain distance.
 0 C = ? K 273
 Standard units of: temperature (social), temperature (physics), energy, mass, density, length, area, volume, speed, acceleration, force, pressure, and specific heat capacity °C, K, J, kg, kg/m³, m, m², m³, m/s, m/s², N, Pa, and J/kg °C
 Density and pressure equations Ρ=m/v, p=F/A
 Pressure direction of effect and equation of height Pressure acts in all directions, p=hρg
 Kelvin temp of a gas is proportional to the Avg KE of its molecules
 What happens when a solid melts to form a liquid? Thermal energy is converted into kinetic to break the particles apart and allow them to move freely, then after melting the thermal just transfers straight to the liquid
 How do particles behave in solids, liquids, and gases? Solids: locked together, evenly spaced, usually most dense, vibrating. Liquids: freely flowing over each other, can be poured. Gases: take up whole volume of container, bouncing off molecules and the walls, exerting an outward pressure.
 Whats specific heat capacity The energy required to change the temp of an object by 1 degree c per kg
 Change in thermal energy equation ?Q=mc?T
 What temperature is absolute zero and what does it mean? -273°C or 0K, particles have 0J kinetic energy and are at a complete standstill. There is no colder temperature as energy=0
 Gas temperature/volume pressure equations P₁/T₁=p₂/T₂, p₁V₁=p₂V₂
 Whats the motor effect A wire carrying a current creates a magnetic field . This can interact with another magnetic field, causing a force that pushes the wire at right angles
 What is magnetically hard? Substances that can be permanently magnetised
 Magnetically soft Those materials that are easily magnetised and demagnetised.
 Why are some materials magnetised but not others? Most of the electrons spin in the same direction. This makes the atoms in these substances strongly magnetic
 How are simple electromagnets made Wrapping a wire around an iron nail and running current through the wire.
 Loudspeaker 1.a current in the coil creates a magnetic field 2.the magnetic field interacts with the permanent magnet generating a force, which pushes the cone outwards 3. the current is made to flow in the opposite direction 4.the direction of the magnetic field reverses 5. the force on the cone now pulls it back in repeatedly alternating the current direction makes the cone vibrate in and out 6. the cone vibrations cause pressure variations in the air - which are sound waves
 How to make an electromagnet stronger More turns of coils, soft iron core, stronger magnet
 What is electromagnetic induction A voltage is induced in a conductor or a coil when it moves thru a mf or when a mf changes thru it
 Whats a split ring commutator Two metal half rings connecting either end of the rotor coils to the brushes
 Slip ring Passes electrical signals and power across a rotating interface using sliding electrical contacts.