physics

• motor effect

  a current carrying wire in a magnetic field will experience a force
• in the motor effect, the current carrying wire must be perpendicular to the magnetic field
• a magnetic field is always produced when a current flows through a material
• generator effect

  an electric current is generated by moving a wire in a magnetic field
• dynamos have split ring commutators and produce d.c current, alternators have slip rings and carbon brushes and produce a.c current
• explain how an electromagnetic induction (generator effect) is used in dynamos.

  • a coil of wire is turned inside a magnetic field, which induces a magnetic field, and current, in the coil of wire.
  • the coil is connected to a commutator which switches the connections every half-turn.
  • this causes the induced current in the external circuit to be in one direction (d.c.). 
• a loudspeaker converts electrical signals into soundwaves through the motor effect, a microphone coverts sound waves into electrical signals through the generator effect
• how do transformers work

  • primary coil generates an alternating magnetic field when supplied with an alternating current
  • this then induces an alternating magnetic field in the iron core
  • this induces an alternating voltage in the secondary coil causing an alternating current if the circuit is complete
• step up transformers increase the voltage and decrease the current, and have more turns on the secondary coil

  step down transformers decrease the voltage and increase the current, and have more turns on the primary coil
• comets have elliptical orbits and are made of ice and dust
• asteroids are mostly rock and metal
• a nebula is a large cloud of gas and dust
• gravity pulls together the dust and gas in a nebula to form a protostar
• as a protostar gets bigger is becomes hotter, more dense and nuclear fusion begins
• the energy released from nuclear fusion creates an outward pressure that balances against the inward pressure from gravity.
• • a main sequence star only fuses together hydrogen to make helium. 
  • red giants or red super giants, nuclear fusion can form heavier elements up to iron
  • elements heavier than iron are formed by supernovas. 
• the magnitude of the velocity must increase for an object to stay in orbit
• cmbr is cosmic microwave background radiation
• red side of emission spectra has a longer wavelength
• some wavelengths of light are absorbed by chemicals in a star's atmosphere
• 
  

  less dense -> more dense : bends towards the normal, wavelength and wavespeed decrease

  more dense -> less dense : bends away from the normal, wavelength and wavespeed increase
• frequency stays the same in refraction
• em waves travel at 3x10^8 m/s in a vacuum
• radio waves can be created by alternating current
• fluorescence is ultraviolet light energy being absorbed and re-emitted as visible light
• white light is the combination of all colours, black is the absence of light
• opaque objects do not transmit light
• the ear drum is a thin membrane that transmit the vibrations of the sound wave to the ossicles 
• the auditory nerve transmits the electrical signals from the cochlea to the brain
• the cochlea converts the vibrations into electrical signals 
• ultrasound reflects off of the boundaries between mediums of different densities.

  the time taken for ultrasound to bounce back to the receiver can be used to calculate the thickness of the medium.
• first law - object will continue at rest or in constant motion unless acted upon by a resultant force

  second law - force on an object is equal to mass times acceleration

  third law - two objects that interact apply an equal and opposite force
• a solenoid is a coil of wire with current flowing
• a moment is the turning effect of a force
• components of a force is two perpendicular forces that have the same effect as a single force
• inertia is the tendency of an object to remain at rest or constant speed