Magnetism and Electromagnetism

• What does the Law of magnetism state?

  Opposite poles attract, similar poles repel
• What type of force is magnetism?

  Magnetism is a non-contact force
• What are the three magnetic elements?

  Iron, Nickel, Cobalt
• Why is steel considered magnetic?

  Steel is an alloy containing magnetic elements
• What are permanent magnets made of?

  Permanent magnetic material
• What happens to an induced magnet when removed from a magnetic field?

  It loses its magnetism
• What is a magnetic field?

  Region around a magnet where force acts
• What does magnetic flux density measure?

  Strength of a magnetic field
• What does the RH grip rule calculate?

  Direction of magnetic field around a wire
• What is a solenoid?

  A wire coiled in a spiral with current
• How can the strength of a solenoid be increased?

  Add more coils, increase current, add iron core
• What is the motor effect?

  Force on a current-carrying wire in a magnetic field
• How can the speed of a motor be increased?

  Place wire at 90 degrees, increase current, use stronger magnets
• What does the LEFT HAND LAW represent?

  Thumb: motion, 1st finger: field, 2nd finger: current
• What is the formula for force in magnetism?

  F = BIL
• What is a simple d.c. motor composed of?

  Coil positioned in a uniform magnetic field
• What does a split ring commutator do?

  Switches direction of current every ½ turn
• How does an A.C. motor differ from a d.c. motor?

  A.C. motor has no split ring commutator
• What happens when A.C. passes through a coil of wire?

  It creates a changing magnetic field around the coil
• What causes vibrations in the air from a microphone?

  Sound waves cause diaphragm to oscillate
• What induces a potential difference (voltage)?

  A wire moves into a magnetic field
• How does the induced p.d. increase?

  By increasing speed, magnetic flux density, or turns
• What happens when the magnet is moved out of the coil?

  The current is reversed
• What is the relationship between p.d. and the number of turns in a coil?

  P.d. is proportional to the number of turns
• What is the formula relating primary and secondary p.d. and turns?

  P.d. (primary) / P.d. (secondary) = turns (primary) / turns (secondary)
• What happens to the p.d. if the second coil has double the turns?

  The p.d. is doubled
• What is the relationship between p.d. and current in transformers?

  P.d. (2nd) x current (2nd) = p.d. (1st) x current (1st)
• What is a magnetic pole?

  Place where magnetic force is strongest
• What are magnetic domains?

  Regions within a material that align magnetically
• What is the difference between A.C. and D.C.?

  A.C. changes direction, D.C. remains constant
• What is the role of carbon brushes in electrical connections?

  Provide a good electrical connection
• What conditions produce maximum p.d.?

  When horizontal and motion is perpendicular
• What happens when motion is parallel to the magnetic field?

  No p.d. is produced
• How are sound waves converted to electrical signals in microphones?

  Diaphragm oscillates due to air pressure changes
• How does magnetization occur in transformers?

  Iron core is magnetized by changing magnetic field