Magnetic Fields Bar Magnet N S

Bar Magnets Field acts as a North Pole would move, i.e. From North to South. Vyrfd Field lines are complete circles.

Earth’s Magnetic Field The magnetic north pole is in the southern hemisphere Denu

Our magnetic field is changing

History of Earth’s Fields

South Atlantic Anomaly

South Atlantic Anomaly

http://www.swpc.noaa.gov/communities/space-weather-enthusiasts

Magnet Field and Current (Conventional Current) Right Hand Grip Rule Fefd

Flemings Left Hand Rule

F = B Il Bil. Length of conductor in field. Force Magnetic Field Strength Current Also known as Magnetic Flux Density.

WHICH WAY WILL IT GO? N S

WHICH WAY WILL IT GO? S N

WHICH WAY WILL IT GO? N S

WHICH WAY WILL IT GO? S N

WHICH WAY WILL IT GO? S N

WHICH WAY WILL IT GO? S N

WHICH WAY WILL IT GO? N S

WHICH WAY WILL IT GO? N S

WHICH WAY WILL IT GO? S N

WHICH WAY WILL IT GO? N S

WHICH WAY WILL IT GO? N S

WHICH WAY WILL IT GO? S N

Mass Spectrometer

Magnetic Flux The magnetic flux density (B) x the area swept out (A) = magnetic flux (theta) Units Webber Dt bring

Electromagnetic Induction A moving charge in a magnetic field experiences a force (to make it move). Therefore moving a conductor in a field will cause a current to flow. This is electromagnetic induction. Or a varying magnetic field over a conductor will also cause a current.

Electromagnetic Induction Flux cutting. The conductor has to cut field lines for an emf to be induced. Discussion: How is the ‘electricity’ made? The demonstrations have shown that ‘making’ electricity involves magnetic fields, but what is really going on? Your students already know that charges moving across a magnetic field experience a force (the BIL force). Now, the metal of a conductor contains mobile charges, the conduction electrons. What happens to these if the conductor is moved across a magnetic field? Consider a conducting rod PQ moving at a steady speed v perpendicular to a field with a flux density B. An electron (negative charge e) in the rod will experience a force (= Bev) (Fleming's left hand rule) that will push it towards the end Q. The same is true for other electrons in the rod, so the end Q will become negatively charged, leaving P with a positive charge. As a result, an electric field E builds up until the force on electrons in the rod due to this electric field (= Ee) balances the force due to the magnetic field. Ee = Bev so E =Bv For a rod of length L, E = V/L and so V/L = Bv Hence the induced EMF E = BLv Clearly what we have here is an induced EMF (no complete circuit so no current flows) and already we can see that more rapid movement gives a greater induced EMF. Now consider what happens when the EMF drives a current in an external circuit. To do this, imagine that the rod moves along a pair of parallel conductors that are connected to an external circuit.

Magnetic Flux Linkage Through a coil of N turns n theta = n BA N theta = NBAcos theta when the magnetic field is along the normal (perpendicular) of the coil face the N theapta = NBA When the coil is turned 180 then N theta = -NBA When the magnetic field is parallel to the coil flux linkage = 0

Faraday's Law The induced emf in a conductor is equal to the rate of change of flux linkage through the circuit. Write this out as an equation. Derive the equation from V= W/Q