Electromagnetic fields

• Moving charges create magnetic fields around them so they interact with magnets
• x means a magnetic field line going into the page, and • means a magnetic field line coming out of the page.
• right-hand grip rule: current flows in the direction of your thumb, magnetic field around the wire is in the direction of your curling fingers.

  
• Electromagnetic induction -> Induction means forced. So you can induce a voltage in a wire or metal rod.

  The wire must be moved through a magnetic field (not parallel to it). The length of the wire/rod that’s inside the field gets a voltage induced across it. Equation: V = BvL

  
• Electric generators work by connecting the ends of the wire/rod to a circuit (e.g. with resistance R) and current flows. So I = V/R, where V is the induced voltage
• Faraday’s Law: changing the magnetic flux through a circuit will produces an induced voltage in the circuit.

  
  

  If the flux changes as time goes on (ie. if there is a ∆ Φ) you’ll

  induce a voltage (V or sometimes ε).

  
  

  Equation: ε = −ΔΦ/Δt

  Negative sign because the voltage opposes the change in flux

  ε means induced emf, a type of voltage, measured in volts -> induced voltage
• For circuits, magnetic flux tells us how much of the magnetic field is passing through the area inside the loop of our circuit. It has the symbol Φ and the unit Wb (webber)

  
  

  Equations: Φ = BA or Φ = BAcos(θ) - if field and area aren't perpendicular.
• Change in flux: ΔΦ = ΔB × A or ΔΦ= B × ΔA

  
  

  Changing the magnetic flux through a circuit will induce a voltage in it.
•  Lenzs Law: The induced current moves in the direction that opposes the change of the flux making it.

  
  

  The change in flux induces a voltage, which forces a current. This new current will make a new magnetic field. This new field opposes the change in flux of the first.

  
  

  So put a minus sign in front of ΔΦ/Δt to make sure that V (and therefore I) opposes the change in flux (ΔΦ)
• Loop moving into magnetic field, flux starts to change inducing an emf to try to keep it out, Loop in magnetic field fully no change in flux through loop so no induced emf, Loop begins to exit magnetic field flux starts to change again inducing an emf now in opposite direction to try to keep it in.