Physics

·         Endoscopes are used to transmit light and information via optical fibres

·         Long wave radio signals can diffract around obstacles and reach their targets                    because they have long wavelengths

·         In a real image, light comes together to form an image at the point where it's seen.           In a virtual image, light appears to come from a point it has not actually been                     through

·         There is an observed increase in the wavelength of light from most distant galaxies.           The further away the galaxies, the faster they are moving and the bigger the                     increase in wavelength. This effect is called red-shift

·         The Big Bang Theory states that the universe began from a very small point, which             exploded and began to expand

·         Microwaves are used for communication

·         Sound waves cannot travel through a vacuum as they travel as vibrations in a                       medium, and in  a vacuum, there is no medium to vibrate

·         Echoes are caused by the reflection of sound waves from a surface

·         The resistance of a thermistor is affected by temperature whereas the resistance              of an LDR is affected by light intensity

·         In parallel circuits, each component is connected separately to the power supply and           each can be turned on or off separately

·         RCCBs cut off the current much faster than fuses

·         Higher power ratings transfer more energy per unit time

·         Fuses should be rated as close as possible but just over the normal operating                     current

·         A step-up transformer is used to increase the potential difference of the                           electricity supply

·         A step-down transformer is used to bring high voltages down to a safe level to use             at home

·         A high potential difference means a low current, as P = I X V

          d.c. flows in one direction only; a.c. changes direction

·         Electronic devices get hotter when used as  components have resistance and current in           the components cause heating

         The current through a diode flows in one direction only. The diode has a very high                   resistance in the reverse direction

·         A diode may be used for half wave rectification of a.c

·    In a chain reaction

• nucleus absorbs a neutron and becomes unstable
• it then splits into two smaller nuclei releasing further neutrons
•  which cause further fission events

·     Nuclear fusion is the joining of two atomic nuclei to form a larger one

·     Nuclear fusion is the process by which energy is released in stars

·     Stars form when enough dust and gas from space is pulled together by gravitational                attraction. Smaller masses may also form and be attracted by a larger mass to become          planets. During the ‘main sequence’ period of its life cycle, a star is stable because the            forces within it are balanced

·    Fusion processes in stars produce all the naturally occurring elements. These elements           may be distributed throughout the Universe by the explosion of a supernova at the end of     its life

·         Alpha particles are the most ionising radiation as they are large and heavy, so they collide       with lots of atoms, causing ionisation

·         Gamma rays are electromagnetic radiation

·         Beta particles are electrons

·         An alpha particle’s structure is that of a helium nucleus

·         The radioactivity of a radioactive isotope will always decrease over time. The half-life is         the average time taken for the number of nuclei of the radioactive isotope in the sample         to halve

·         Hydrogen nuclei fused together in stars to form larger nuclei, which in turn fused together    to form even larger nuclei. Elements heavier than iron are formed when stars explode,            which also cause the distribution of elements throughout the universe

·         Radiation exposure can be dangerous to humans

• Each type of radiation causes ionisation of living cells, which can damage or destroy them
• Minor cell damage caused by radiation can give rise to mutant cells, which can lead to cancer
• High doses of radiation can kill body cells completely and cause radiation sickness
• Outside the body, beta and gamma sources are the most dangerous as they have the most penetrating power
• Outside the body, alpha sources are not very dangerous as they can’t penetrate through the skin very much
• Inside the body, alpha sources are the most dangerous because they do all their damage in a very localised area
• Inside the body, beta and gamma sources are not as dangerous because many of them pass straight out and they are less ionising than alpha sources

·         When sweat evaporates, it cools the skin

• only the fastest particles leave the surface, reducing energy of remaining particles
•   hence the temperature of the sweat decreases
• so, the sweat will now be at a lower temperature than the skin, cooling the skin

·         The specific latent (hidden) heat of fusion (L_F) of a substance is the energy needed to           melt 1kg of the substance at its melting point, with no change in temperature