physics 3

• Transducers


  Devices that detect and convert audio inputs to electric output and vice versa
• Transducers


  • Speakers and microphones
• Transducers


  • Characterized by the production of forces due to a changing electric signal within a magnetic field or a changing field near a current carrying conductor
• Magnets


  Exert either a force of attraction and repulsion
• Attraction


  • Force of attraction happen only possible between an object and a magnet
• Repulsion


  • Force of repulsion happen only possible between an object and a magnet
• An object with a ferromagnetic substance is considered naturally magnet
• An object with a the magnet may also be a permanent magnet or temporarily magnetized ferromagnetic material
• Protons and electrons are basically considered tiny magnets due to the intrinsic magnetic moments of charges
• The magnetism of an electron is a thousand times bigger than that of a proton
• In an atom, the intrinsic magnetic field is mostly due to the ever-moving electrons in the half filled orbital shell where electrons are unpaired and their tiny intrinsic magnetic moments point in the same direction, thus orbital magnetic field arise
• Magnetic materials


  • Iron
  • Nickel
  • Alloys
  • Steel
  • Alnico
• Magnetic materials


  Can be used to make permanent or temporary magnets unlike non magnetized materials which cannot
• Electric field


  Force field surrounding electric charges or group of charges where a force acts on charges within the field
• Magnetic field


  Region where a moving charge experiences a magnetic force
• Magnetic field


  • Is a field of force produced by a magnetic object or particle, or by changing electrical field and is detected by the force it exert on other magnetic materials and moving charges
• Magnetic field sources are essentially dipolar in nature, having north and south
• Magnetic field lines


  • Lines showing the shapes of a magnetic field. A compass placed on such a line will turn so that the needle is aligned with it because of electromagnetic induction
• Magnetic field sources


  • Latch magnet
  • U-shaped magnet
  • Single bar magnet
  • Disk magnet and neodymium
  • Iron nail wrapped w/ current carrying wire
  • Straight current carrying wire
  • Current carrying coil
• Right-hand rule


  This rule is often used in the context of motors and electromagnetic forces. If you extend your thumb, forefinger, and middle finger of your right hand perpendicular to each other, the thumb represents the direction of the force, the forefinger represents the direction of the magnetic field, and the middle finger represents the direction of the current
• Left-hand rule


  This rule is commonly used in the context of generators and the induction of currents. If you extend your thumb, forefinger, and middle finger of your left hand perpendicular to each other, the thumb represents the direction of motion or induced current, the forefinger represents the direction of the magnetic field, and the middle finger represents the direction of the current
• Motors and generators


  A rectangular loop of wire OPQR carrying a current is in a uniform magnetic field as shown in the figure below. What is the direction of the force on PQ? (Use the left-hand rule)
• The force on PQ (middle finger) will be downward
• Wire conductor placed between poles of permanent U magnet

  The direction of current (I) through the wire is also shown. Which arrow (indicated as A, B, C, D) indicates the direction of the force on the wire?
• Refraction


  The bending of light rays due to a change in their speed as it travels from one medium to another with different densities
• As light refracts, the velocity of the wave is altered, its wavelength increases or decreases, but its frequency remains constant
• Amount of bending


  Depends on change in speed and angle of the incident ray
• If light is entering the new substance from straight on (at 90° to the surface or at normal), the light will still slow down, but it won't change direction at all or it will not bend
• Speed of light in different media

  • Vacuum: 300,000 km/s
  • Air: <300,000 km/s
  • Water (20°C): 225,000 km/s
  • Glass: 200,000 km/s
  • Diamond: 124,120 km/s
• Index of refraction (optical density)

  The ratio of velocities of light as it passes from a vacuum into another medium
• A higher refractive index shows that light will slow down and change direction more as it enters the substance
• Angle of incidence


  The angle at which light hits the surface
• Angle of refraction


  The angle at which the light bends as it enters the new medium
• The angle of refraction increases as the angle of incidence increases
• Critical angle


  The angle of incidence that produces an angle of refraction of 90° in the medium
• If light travels into a substance from higher to lower refractive index, it speeds up and bends away from the normal line
• If light enters any substance from lower to higher refractive index, it slows down and bends towards the normal line
• Lens


  A shaped transparent material that refracts light to create an image
• Features of concave and convex lenses

  • Principal axis
  • Vertical axis
  • Focal point
  • 2F
  • Focal length
• Images formed by lenses

  • Real, inverted, between F and 2F on the other side, smaller/demagnified (<1)
  • Real, inverted, at 2F on the other side, same size (1)
  • Real, inverted, beyond 2F on the other side, larger/magnified (>1)
  • No image formed, focal and chief rays don't meet
  • Virtual, upright, beyond 2F behind the object, highly enlarged (>1)
  • Virtual, upright, between F and V, smaller/demagnified (<1)