day before

Cards (92)

  • what is a magnetic field?
    • region surrounding a magnet where another magnet or magnetic material experiences a non-contact force
  • what does a magnetic compass contain?
    • a small bar magnet that points in the direction of the earths magnetic field
  • what is produced when current flows through a conducting wire?
    • magnetic field produced around the wire
  • what determines the strength of the magnetic field around a current-carrying wire?
    • the magnitude of the current flowing through the wire
    • the distance from the wire
  • what is a solenoid?
    • a coil of wire which when current passes through creates a strong magnetic field
  • describe the magnetic field found inside the solenoid
    • strong and uniform
  • what is an electromagnet?
    • a solenoid with an added iron core
    • adding the iron core increases the strength of the magnetic field
  • what is the motor effect?
    • when a force is exerted between a magnetic field and a current-carrying conductor placed in that field
  • what factors affect the size of the force on a current-carrying wire in a magnetic field?
    • the magnitude of the current flowing through the conductor
    • the strength of the magnetic field that the conductor is placed in
  • if the direction of current in a current-carrying wire placed in a uniform magnetic field is reversed what happens to the force?
    • direction of the force is reversed
  • if the strength of the current in a current carrying wire is increased what happens to the force?
    • the strength of the force is increased
  • what criteria must be met for the equation linking force, magnetic flux density, current and length to hold?
    • conductor must be at right-angles to the magnetic field it is placed in
  • what is the unit for magnetic flux density?
    • Tesla, T
  • How does an electric motor work?
    • coil of wire, carrying a current is placed in a magnetic field
    • forces on the two sides perpendicular to the field experience forces in opposite directions
    • causes a rotational effect
  • how do loudspeakers make use of the motor effect?
    • used to convert variations in the current of an electrical circuit into the pressure variations which produce audible sound
  • explain how a loudspeaker works
    • cone with a wire wrapped around it connected to an a.c power supply & placed in a permanent magnetic field
    • when current flows through the wire, creates a second magnetic field which interacts with the permanent field
    • produces a force which causes the cone to vibrate
  • how is the pitch of sound changed in a loudspeaker?
    • frequency of the a.c current is altered
    • creates a different frequency of vibration in the cone
  • give two examples of transverse waves:
    • em waves
    • seismic s-waves
  • give two examples of longitudinal waves
    • sound waves
    • seismic p-waves
  • what are the two parts of a longitudinal wave called?
    • compressions and rarefactions
  • what is a waves amplitude?
    • maximum displacement of a point on a wave from its undisturbed position
  • what is the unit used for frequency?
    • Hertz, Hz
  • what is wave speed?
    • speed at which the wave moves or at which energy is transferred through a medium
  • what does a wave transfer?
    • energy
  • what word is used to describe when a wave bounces off a surface?
    • reflection
  • how do sound waves travel through a solid?
    • particles in the solid vibrate and transfer kinetic energy through the material
  • what is the frequency range of human hearing?
    • 20Hz - 20kHz
  • what are ultrasound waves?
    • waves which have a higher frequency than the upper human limit of hearing
  • give an example use for ultrasound waves
    • medical or industrial imaging
  • what natural event causes seismic waves to be produced?
    • earthquakes
    • produce both p-waves and s-waves
  • what medium do p-waves travel through?
    • solids and liquids
  • what medium do s-waves travel through?
    • solids
  • what technique is used to detect objects in deep water and measure water depth?
    • echo sounding
    • high frequency sound waves are emitted, reflected and detected
    • time difference between emission and detection alongside wave speed are used to calculate distances
  • what type of spectrum do em waves form?
    • continuous
  • how do the speeds of em radiation differ in a vacuum and in air?
    • same speed
  • what property of waves in different mediums causes refraction?
    • velocity
    • wave speed slower in denser materials, causing refraction
  • in which direction do waves refract when entering a denser medium?
    • bend towards the normal
    • angle of refraction is less than the angle of incidence
  • what type of waves can be produced by oscillations in an electrical circuit?
    • radio waves
  • how can radio waves create an alternating current in a circuit?
    • when radio waves absorbed they can induce oscillations in a circuit with the same frequency as the waves themselves
  • where do gamma rays originate from?
    • changes in the nuclei of atoms