day before

• 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