Physics

• Evaporation process (4 marks)?

  1. evaporation happens when particles with above average energy are able to escape the water leaving lower energy particles behind.
  2. This decreases the average energy of the remaining particles
  3. Since temperature is proportional to the average particle energy, lower average energy means that temperature decreases so cooling occur
• Changes that happen when a liquid boils to form a gas?

  • particles move apart
  • particles gain kinetic energy
  • they leave the liquid
• soft magnets lose their induced magnetism quickly whereas hard magnets remain magnetic
• magnetic field is a region where magnetic materials experience a force
• magnetic field lines are used to show the size and direction of magnetic fields. They always point from North to South.
• magnetism is induced in some materials when they are placed in a magnetic field
• Describe a method to reveal the magnetic field of a bar magnet (3):

  • place compasses around the bar magnet
  • draw arrows for each compass point
  • drae a line through the compasses following the arrow direction
• magnetic matieral is a material that becomes magnetised when placed in a magnetic field.
• magnetic field around a straight wire:

  • concentric circles of magnetic fields with the wire in the center
• magnetic field structure around a flat circular coil:

  • concentric ellipses of magnetic field lines around the coil

  A) concentric ellipses
• • magnetic field inside a current-carrying solenoid (coil of wire) is strong and uniform
  • ends of a soilenoid act like the north and south pole of a bar magnet
  • this type of magnet is called an electromagnet

  
• Life cycle of a star bigger than the sun?

  • Nebula (cloud of dust and gas) that is drawn together by the force of gravity into a protostar (no fusion)
  • The star gets denser and hotter due to more frequent particle collisions
  • Eventually the temperature gets hot enough for the fusion of hydrogen nuclei which forms helium --> Main sequence star formed
  • When the star runs out of hydrogen, it expands as it cools and turns red to form a red supergiant which explodes in a supernova
  • supernova throws the outerlayer of dust and gas into space, leaving behind a dense neutron star or a black hole.
• Life cycle of a star the same size as the sun:

  • Nebula (cloud of dust and gas) that is drawn together by the force of gravity into a protostar (no fusion)
  • The star gets denser and hotter due to more frequent particle collisions
  • Eventually the temperature gets hot enough for the fusion of hydrogen nuclei which forms helium --> Main sequence star formed
  • When the star runs out of hydrogen, it expands as it cools and turns red and forms a red giant. It then becomes unstable and ejects its outerlayer of dust and gas.
  • A white dwarf with a hot, dense solid core is left behind.
• Describe 4 ways to increase the strength of an electromagnet//solenoid:

  Increase current

  Increase strength of magnets

  Add a soft iron core in the middle

  Reduce the length of the solenoid but keep the number of turns the same
• Motor effect:

  A current carrying wire in the presence of a magnetic field will experience a force. This is called the motor effect.
• Magnetic field strength is measures is Teslas (T)
• Absolue magnitude:

  Measure of brightness of a star
• Construction of an electromagnet:

  A coil of wire

  Carrying a current

  Around a core made of a soft magnetic material
• Fusion:

  The joining of two small, light nuclei to form a larger, heavier one and release energy
• Catalyst for cracking: silica and alumina
• ideal temperature for cracking - 600 - 700 degrees celcius
• comets orbit stars
• Describe 4 ways to make the motor spin in an opposite direction:

  • Swap current
  • Switch the poles of the magnet
• How to prove direct proportionality:

  • Straight line gradient which passes through (0,0)
• Using a charged nozzle (static electricity)

  → paint particles become positively charged, 

  → Particles repel each other

  → Paint produced a thinner coat
• Red shift:

  • light emmitted by stars increase in wavelength
  • the light colours move to the red end of the spectrum
  • due to the doppler effect the frequency decreases and it moves away from us.
• Half life - average time number of radioactive nuclei to decay by half.
• Factors affecting stopping distances:

  • Vehicle speed - the greater the speed, the greater the vehicle's braking distance will be
  • Vehicle mass - a heavy vehicle takes longer to stop
  • Road conditions - wet or icy roads make it harder to decelerate
  • Driver reaction - time a driver's thinking distance depends on their reaction time. Being tired, or intoxicated (i.e. alcohol, or drugs) can increase reaction time