Physics Paper 1

• Transverse waves- vibrations are perpendicular to the direction that the wave travels

  e.g. all electromagnetic waves, s-waves and water waves
• Longitudinal waves- vibrations are parallel to the direction that the wave travels

  • waves squash up and stretch out, making compressions are rarefactions
  • e.g. sound waves, P-waves
• EAR

  • sound waves cause eardrum to vibrate
  • vibrations are passed on to tiny bones called ossicles
  • go through semicircular canal to the cochlea
  • cochlea turns vibrations into electrical signals and send them to the brain
  • brain interprets signals as sounds of different pitches and volumes
• P waves:

  • longitudinal
  • travel through solids and liquids
  • faster than S - waves
• S- waves:

  • transverse
  • travel through solids
  • slower than P waves
• angle of incidence = angle of reflection
• colour filters are used to filter out different wavelengths of light, so that only certain colours (wavelengths) are transmitted- the rest are absorbed
• A converging lens (convex) bulges outwards in the middle. It causes rays of light to be brought together (converge) at the principal focus.
• A diverging lens (or concave) lens caves inwards. It causes parallel rays of light to spread out (diverge).
• A real image is formed when the light rays actually come together to form the image.
• A virtual image is when the light rays from the object appear to be coming from a completely different place to where they're from.
• The more powerful the lens, the more strongly is converges the rays of light, so the shorter the focal length.
• An object 2F (focal lengths) from the lens produces a real, inverted image the same size as the object at 2F on the other side of the lens.
• An object between F and 2F will make a real, inverted image bigger than the object beyond 2F.
• An object nearer than F will make a virtual image the right way up, bigger than the object and on the same side of the lens.
• A diverging (concave) lens always produces a virtual image. The image is always the right way up, smaller than the object and on the same side of the lens as the object.
• Radio waves are transmitted through the body without being absorbed.
• Some wavelengths of microwaves can be absorbed, causing heating of cells, which may be dangerous.
• Infrared radiation and visible light are mostly reflected or absorbed by the skin, causing some heating too. Infrared radiation can cause burns if the skin gets too got.
• Ultraviolet has a higher frequency and so is more dangerous. It is a type of ionising radiation and when absorbed it can cause damage to cells on the surface of your skin, which can lead to mutations and skin cancer.
• X-rays and gamma rays are also ionising, so they can cause mutations and damage cells (which leads to cancer). They have even higher frequencies so transfer even more energy so they can pass through the skin and be absorbed by deeper tissues.
• Black, dull surfaces are better emitters of radiation than white ones.
• EM waves are made by oscillating electric and magnetic fields.
• Radio waves are used mainly for communication and broadcasting.
• Micro waves and radio waves are used by satellites.
• Microwave ovens also use microwaves.

  • microwaves are absorbed by the water molecules in the food
  • heat up water molecules which then transfer energy to the rest of the food by heating- which quickly cooks the food
• Infrared radiation can be used to increase or monitor temperature

  • infrared radiation is given out by all objects
  • infrared cameras can be used to detect infrared radiation and monitor temperature
  • uses include: thermal imaging, infrared sensors in security systems
• Infrared can also be used to transfer information- Tv remote controls and optical fibres.
• Photography uses visible light
• Ultraviolet is used in fluorescent lamps. The lamps use UV to emit visible light. Bank notes and passports have special markings that only show under UV light.
• X-rays are used to view internal structures of objects and materials, including our bodies. Used in hospitals but also in airport security scanning.
• Gamma rays are used to sterilise medical instruments- they kill microbes.
• Gamma radiation is also used in tracers to detect cancer.
• Gamma radiation is used in cancer treatments- they kill the cancerous cells.
• Thomas- Plum Pudding Model- a ball of positive sphere with negative electrons embedded in it.
• Alpha particles were suppose to go straight through the thin gold foil when were fired from a beam but most went straight through and some were deflected more than expected.
• An atom is a positively charged nucleus surrounded by negatively charged electrons.
• An inner electron can move up to a higher energy level if it absorbs electromagnetic radiation with the right amount of energy.
• Isotopes of an element have the same number of protons but a different number of neutrons.
• An alpha particle is made of 2 neutrons and 2 protons. They only travel a few cm in the air and are stopped by a piece of paper. They are strongly ionising but not very penetrating.