P1 markings

• Explain how doubling the speed of a vehicle increases the braking distance

  • increases kinetic energy by a factor of 4
  • this increases braking distance because more energy needs to be dissipated
• Transmission of waves

  • occurs when waves pass through a material, such as light passing through clear glass window
  • amount of transmission depends on the material's transparency
• Absorption of waves

  • occurs when a material takes in the energy of a wave, such as sound absorbed by foam or light absorbed by any black surfaces
  • absorbed energy may cause the material to heat up or undergo other changes
• 2 properties that are common to all EM waves

  • they are transverse waves
  • all travel at the same speed in a vaccum
• Describe the precautions that should be taken when working with radioactive sources to ensure safety

  • use tongs
  • store sources in lead-lined containers
  • minimise exposure time
• Explain how the red-shift of light from distant galaxies supports the BBT

  • light from galaxies shifts to longer wavelengths
  • proves that galaxies are moving away and Universe is constantly expanding
• Describe the life cycle of a star similar to the Sun, including the forces involved in each stage

  • the star forms from a nebula, which is a cloud of dust and gas pulled together by gravity
  • it becomes a main sequence star when nuclear fusion of hydrogen occurs, releasing energy
  • the star expands into a red giant when the hydrogen runs out and helium starts to fuse
  • finally, it collapses into a white dwarf after shedding its outer layers
• Explain how CMBR provides evidence for the BBT

  • radiation detected from all directions
  • evidence of cooling universe since the Big Bang
  • supports the BBT
• Process of nuclear fusion, including how energy is released during it

  • two light nuclei combine to form a large, heavier nucleus
  • releases energy
  • due to mass being converted to energy
• Explain why nuclear fusion does not happen at low temperatures and pressures

  to overcome repulsion between nuclei
• Explain the challenges of creating a practical and economic nuclear fusion power station

  • very expensive to provide the energy required to generate high temperatures and pressures needed
  • containing the heat/pressure is difficult, no solid materials can withstand the heat, so magnets/expensive materials must be used
  • maintaining extreme temperature and pressures consumes more energy than the fusion process currently generates, making it uneconomic
• Explain a way that radioactive substances are used in diagnosing medical conditions

  • radioactive tracers injected into body to emit gamma rays which are detected to produce images of organs
  • PET scanners detect the gamma rays emitted provided detailed 3D images of metabolic activity
• Why isotopes used in PET scanners must be produced nearby?

  • they have very short half-lives so they decay too quickly for long-distance transport
• Describe how and why the atomic model has changed over time

  • Dalton = atoms are indivisible spheres
  • Thomson = discovery of electrons (plum pudding model)
  • Rutherford = positive nucleus discovered by alpha scattering
  • Bohr = electrons orbit in fixed shells
  • Chadwick = neutrons found in nuclei
• Describe the processes of beta-minus decay and beta-plus decay

  • Beta-minus = neutron into proton, releases an electron
  • Beta-plus = proton into neutron, releases a positron
• Explain how atomic number and mass number change during alpha, beta and gamma decay

  • alpha = mass decreases by 4, proton number decreases by 2
  • beta = proton no increases by 1, mass unchanged
  • gamma = no change in mass or proton number
• Explain use of ultrasound in sonar

  • ultrasound waves emitted and reflect back from underwater objects
  • the time taken for the reflection is used to calculate distance using wave speed
• Explain use of ultrasound in foetal scanning

  • ultrasound waves are emitted and reflect back from boundaries between different tissues
  • the reflections are used to create detailed images of the unborn baby
• Explain how the ear converts sound waves to help us hear sound

  • vibrations in air cause eardrum to vibrate
  • vibrations transmitted through ossicles to cochlea
  • cochlea converts vibrations into electrical signals for the brain
• Chain reaction in nuclear fission

  • neutrons emitted in one fission go on to hit other U-235 nuclei
  • neutrons emitted in one fission go on to cause a chain reaction
• Control rods in nuclear fission

  • rods absorb neutrons
  • controls number of fission
  • varies rate of thermal energy released
• Moderator in nuclear fission

  • slows down neutrons
  • makes them more likely to cause fission
• Explain how difference in wavelengths show that the Universe is expanding

  • there is an increase in wavelength of light
  • shows galaxies are moving away from Earth
• State what causes the nebula to collapse

  gravitational attraction
• Explain why the nebula stops collapsing as it becomes a main sequence star

  • gravity causing an increase in temperature
  • until hot enough for fusion
  • until balance between gravity and fusion
• Explain why the temperature of colour P reaches a constant value, even though the heater remains switched on

  • P is absorbing radiation
  • P is also emitting radiation
  • Rate of emission increases with temperature
  • Temperature is constant when rate of emission = rate of absorption
• Describe the process that occurs after nebula to produce the conditions necessary for nuclear fusion in a new star

  1. nebula collapses
  2. under gravity
  3. very high temperatures/pressures reached so increase in KE of particles
• Explain how a nebula may evolve into a main sequence star

  • nebula as a cloud of gas/dust
  • gas pulled together
  • by gravitational force
  • temperature increase
  • hot enough for nuclear fusion
• Describe what is meant by the Big Bang Theory

  • expansion of space
  • origin of Universe
  • Universe is still expanding
• Describe how a reflecting telescope forms an image of a distant object

  • mirror
  • which is converging
• State what the eyepiece of a telescope is intended to do to the image

  magnifies it
• Evidence for geocentric model

  • Sun, Moon, starts, planets moving across the sky not just orbiting
  • in the same direction
  • pattern is repeated
  • appear to be going around the Earth
  • same every day
• Evidence against geocentric model

  • moons of Jupiter appear to orbit Jupiter
  • movement of Sun not quite the same each day
  • planets do not move in a simple path
• Our Sun will go through...

  white dwarf
• Steady State Theory

  • universe is expanding
  • universe did not have a beginning
• Galaxy which contains our Sun is called...

  the Milky Way
• Describe one method they use to search for signs of life on the planet Mars

  • lander e.g. drones that takes photos
• Explain why telescopes that search for planets are not on the Earth's surface

  • image is distorted
  • planets very small
  • can detect different parts of em spectrum that are not detectable on Earth
• Doppler effect

  the change in frequency of a wave due to the relative motion of the source and the observer
• Red shift as evidence for expanding Universe

  • light shifted to red end of spectrum
  • light waves are stretched so wavelength increases
  • frequency means source moving away
  • shows galaxies are moving away from us
  • greater red shift indicates galaxy moving away faster
  • further galaxies give greater red shift
  • red shift = increase, blue shift = decrease
  • therefore galaxies are moving apart