physics paper 2

• WAVES

  LONGDITUDINAL: direction of oscillation is PARALLEL to direction of energy transfer

  EXAMPLES: sound, seismic P waves
• WAVES

  TRANSVERSE: direction of oscillation is PERPENDICULAR to direction of energy transfer

  EXAMPLES: water waves, seismic S waves, EM waves
• WAVE EQUATION- how to calculate

  RIPPEL TANK: measure 10 wavelengths to find one, use frequency to calculate wavespeed

  TRAY: calculate wavespeed by total d/t

  SOUND: obtain time for echo to return, calculate v by total d/t
• FISSION

  FISSION is the splitting of a (heavier) nucleus (like Uranium-235) into two 'daughter' nuclei, releasing energy (mostly kinetic/heat)

  that can then used to generate electricity.
• FISSION

  Fission is INDUCED by a nucleus absorbing a neutron, making it more unstable (U-236). It also releases up to 3 more neutrons

  these go on to induce more fission. This is a CHAIN REACTION.
• FUSION

  FUSION is the joining together of two(lighter) nuclei (such as heavy hydrogen-2, also called deuterium, into helium), releasing

  energy (kinetic and EM radiation).
• FUSION

  This happens in the SUN, but it is proving difficult to harness the energy produced by fusion in the reactors being developed.
• SATELLITES

  NATURAL & ARTIFICIAL SATELLITES ORBIT THE EARTH. GEOSTATIONARY SATELLITES ORBIT ABOVE THE SAME POINT ON THE EQUATOR.
• SATELLITES

  Their orbits are circular, which means that while their

  SPEED is constant, their VELOCITY is always changing, due to their DIRECTION changing. It's ACCELERATING, but not getting faster!

  Used for GPS, TV & communications.
• SATELLITES

  CENTRIPETAL FORCE always acts towards the centre of the orbit.
• SATILLITES

  If a satellite has an ELLIPTICAL ORBIT, it gets

  FASTER as it gets CLOSER to the Earth, and vice verse.

  Used for reconnaissance & weather.
• RED SHIFT

  THE WAVELENGTH OF LIGHT FROM DISTANT GALAXIES IS RED-SHIFTED:

  STRETCHED BECAUSE THE GALAXIES ARE MOVING AWAY FROM US.

  Moreover, more distant galaxies are MORE RED-SHIFTED,

  which means they're RECEDING at a greater rate. This suggests that they all originated from the same position. This is used as evidence

  for the BIG BANG THEORY.
• CMBR

  CMBR: COSMIC MICROWAVE BACKGROUND RADIATION is also evidence: microwave radiation is detected from every direction of space, which could be from the matter still cooling down from the Big Bang.
• LIFE CYCLE OF STARS

  NEBULA -> PROTOSTAR -> MAIN SEQUENCE (spits at MS, two possibilities)

  MAIN SEQUENCE -> RED GIANT -> WHITE DWALF -> BLACK DWALF

  MAIN SEQUENCE -> SUPER RED GIANT -> SUPERNOVA -> BLACK HOLE
• FISSION SUMMARY

  -The nucleus undergoing fission SPLITS into two, smaller nuclei, roughly equal size. 2 or 3 neutrons are emitted and gamma rays. All products have KINETIC energy. The neutrons may start a CHAIN reaction.

  -In a nuclear reactor the chain reaction is controlled using CONTROL RODS to absorb neutrons.
• IRRADIATION


  when radioactive material is outside your body, but the radiation can travel into your body
• CONTAMINAION


  When radioactive material is present inside your body or on your skin
• FUSION

  -the joining of two light nuclei to form a heavier nucleus

  -Some of the mass is converted into energy of the radiation that gets emitted
• RADIATION

  -All types of nuclear radiation are ionising

  -Alpha is the most ionising because it has the biggest charge and mass
• SOUND & SEISMIC WAVES

  When sound meets a boundary between two mediums (materials), some sound is TRANSMITTED (passes through), while some is REFLECTED. The resulting echoes can be timed to build up a image of what's out of view e.g. a baby in a womb, or schools of fish underneath a boat (SONAR).

  The fact that seismic P-waves (longitudinal) pass through the centre of the Earth while S-waves (transverse) do not suggests that it has a MOLTEN (liquid) CORE
• SOUND & SEISMIC WAVES

  If light reflects off a smooth surface (e.g. mirror), this is SPECULAR REFLECTION. The angle of REFLECTION is equal to the angle of INCIDENCE, relative to the NORMAL.

  A rough surface will SCATTER light - this is DIFFUSE REFLECTION.
• REFRACTION

  WHEN WAVES ENTER A NEW MEDIUM (MATERIAL), THEIR SPEED CHANGES, AS DOES THEIR ANGLE.

  -if the wave slows down it bends TOWARDS the NORMAL

  -that means the angle of REFRACTION is SMALLER than the angle of INCIDENCE
• REFRACTION

  If SPEED decreases, WAVELENGTH also does, while FREQUENCY stays constant.

  -Light DISPERSES through a prism because different wavelengths are refracted different amounts (BLUE most, RED least).

  -When the light exits, it speeds up again, and it bends AWAY from the NORMAL
• COLOUR & BLACKBODIES

  WE PERCEIVE DIFFERENT COLORS WHEN DIFFERENT WAVELENGTHS

  OF LIGHT ARE ABSORBED BY THE RETINA. An object will appear a certain color as it REFLECTS those wavelengths and ABSORBS others.A BLACKBODY IS A THEORETICAL OBJECT THAT PERFECTLY ABSORBS AND EMITS ALL WAVELENGTHS OF RADIATION (it does not reflect radiation). We can apply this model to stars and planets as an approximation. If the rate of ABSORPTION is greater than the rate of EMISSION, its temperature increases. But this then in turn increases the rate of emission.
• NUCLEAR RADIATION

  All three types of nuclear radiation (and some other EM waves) IONISE other atoms, which can be dangerous for living things. They can be detected with a Geiger-Muller (GM) tube. BACKGROUND RADIATION: e.g. cosmic rays, radon gas (rocks), nuclear weapons, medical equipment. source Background count should be taken first, then subtracted from count with source to give correct count. NEUTRONS can also be ejected from nuclei under certain conditions. These are very dangerous as they can be absorbed by other nuclei to make them unstable they're now radioactive.
• ELECTRICAL POWER, AC/DC, MAINS & SAFETY

  Mains electricity is A.C. (alternating current), resulting from an ALTERNATING (both of these reverse direction at a frequency of 50Hz, at least in the UK).

  -NEUTRAL WIRE stays at 0V while LIVE wire changes between + and - potentials, which average out to a p.d of 230v- UK mains voltage
• FUSE

  every plug has a FUSE connected to the live wire, it's a thin metal metal wire in a wire in a tube that's designed to melt or blow if there's a fault that causes a high current
• ELECTRICAL POWER, AC/DC, MAINS & SAFETY


  EARTH WIRE is a safety feature, acts as an 'escape route' for currents that would otherwise shock if the appliance is touched. Not need for DOUBLE INSULATED appliance
• TRANSFORMERS

  A.C. input to primary coil induces alternating magnetic field in soft iron core (easily magnetised & demagnatised); this induces current in the secondary coil. The side with the most turns has the greater P.d. N & V are proportional, so x2 turns means x2 the p.d. (like this step-up transformer).
• NATIONAL GRID

  Power stations produce a relatively high current. If this went straight into the grid, a huge amount of energy/power would be lost as heat due to the resistance of the cables .

  -A STEP-UP TRANSFORMER increases the voltage , which DECREASES the CURRENT, reducing the power lost due to heating in the cables.

  -A STEP-DOWN TRANSFORMER reduces the voltage down to a safer and usable 230V for homes & businesses