Magnetic Field

how do the magnetic field lines of magnets look like

• they form closed loops

• moving from NORTH to SOUTH pole

what is tesla and what is its unit

• its a unit to measure magnetic fields

• its unit is 1 N/Am

  • newton per ampere metre

what is orsted’s law

• current running through a wire produces a magnetic field

• the magnetic fields appear as circles with the wire in the center

what is the first right hand rule

• what is it used for

it is used to find

• the direction of magnetic field lines

  • direction fingers are curling

• direction of current

  • direction thumb is pointing in

what is the second right hand rule

• what is it used for

it is used to find the direction of the force acting on a wire

• arm: direction of current

• fingers bent 90 degrees: direction of magnetic field

• thumb: direction of force

what can be said about the direction of the force from a magnetic field on a current

the force is perpendicular to both the magnetic field and the current

formula to find magnitude of force from a magnetic field acting on a wire

F = I L B sinθ

• F: magnitude of force

• I: current

• L: length of wire running though magnetic field

• B: magnetic field

• sinθ: angle between current and magnetic field

  • max. value: 1 (sin90)

  • when current is perpendicular to magnetic field lines

  • min. value: 0 (sin0)

  • when current is parallel to magnetic field lines (NO FORCE on wire)

formula to find magnitude of force on a single moving charge

• also known as Lorentz force

F = qvB sinθ

• q: charge of electron

• v: velocity (m/s)

• B: magnetic field

• sinθ: angle between current and magnetic field

what is the third right hand rule

• what is it used for

used to find the direction of force on a particle

• arm: direction of current velocity

• fingers bent 90 degrees: direction of magnetic field

• thumb: direction of force

  • +ve charge: force in direction of thumb

  • -ve charge: OPPOSITE direction

what is faraday’s law of induction

a changing magnetic field will induce an emf in a loop of wire

what is emf and what is it used for

it is electromotive force

• it is what causes electrons to move and form a current

what is magnetic flux and whats its symbol

it is a measure of the magnetic field running through a loop wire

• Φ or Φ_B (phi)

what causes emf when a current runs through a wire

the change in magnetic flux

what is the formula for magnetic flux

Φ = B A cosθ

• B: magnetic field

• A: area of the loop

• cosθ: angle between the magnetic field and a line perpendicular to the face of the loop

what is the unit of magnetic flux

Tm² or Wb

• Tm²: tesla meter square

• Wb: webers

how does magnetic flux affect emf

• as magnetic flux decreases, emf increases

• as magnetic flux increases, emf decreases

what is the formula to find emf

E = ▵Φ / ▵t

• ▵Φ: change in magnetic flux

  • Φ_final - Φ_initial

• ▵t: time taken for change to occur

what is Lenz’s Law

Lenz’s Law states that the magnetic field generated by the induced current will be in the direction opposite the change in magnetic flux

formula for emf when conductor is perpendicular to the loop

E = BLv

• B: magnetic field

• L: length of the conductor

• v: velocity of conductor