EMI Flashcards
magnetic flux
the magnetic flux through a plane surface is the product of the area and the component of the magnetic flux density (b) perpendicular to that area
weber
one weber is the amount of magnetic flux through a surface if a magnetic field of flux density of one Tesla exists perpendicularly to an area of 1m^2
magnetic flux linkage
the product of the number of turns of the coil and the magnetic flux through each turn
faradays law
the MAGNITUDE of induced emf is DIRECTLY PROPORTIONAL to the rate of change of magnetic flux LINKAGE
Lenz law
FYI :
induced current can also be created by the change in magnetic flux when a metal is rolling (direction found by FRHR (higher potential on tip of finger which means current flows in that direction since electrons move downwards) the force inflicted by this induced current is then determined by the FLHR
induced current can only be in a closed circuit / closed electrical paths - like no start and end so that means a circular closed rod can have induced current but a straight rod with both ends unconnected cannot
the polarity of the induced emf (seen through the negative sign in emf wrt change in magnetic flux) is such that it tends to produce a current that creates a magnetic field so as to oppose the change in magnetic flux
explaining the effects of induced current in solenoid when a magnet enters
reminder to print notes for superposition and all other phy topics from drive lol
As the N-pole approaches, the magnetic flux LINKAGE through the solenoid increases. By Faraday’s law, an e.m.f. is induced. An induced current caused by induced emf flows because it is a closed circuit. By Lenz’s law, the induced current in the solenoid will produce a magnetic field in the opposite direction as the magnet to oppose the increase in the flux linkage (hence the current is flowing clockwise when viewed from top / left / from left to right etc)
when the tube is in the middle of the b field, the b field value is constant and the magnetic flux linkage through the coil is con start and there is no current induced
explaining damping effects (due to closed circuit)
As the N-pole approaches, the magnetic flux linkage through the solenoid increases. By Faraday’s law, an e.m.f. is induced. An induced current caused by induced emf flows because it is a closed circuit. By Lenz’s law, the induced current in the solenoid will produce a magnetic flux to oppose the increase in the flux linkage by generating a magnetic field in the opposite direction as the magnet. AS THERE ARE CLOSED ELECTRICAL PATHS, eddy currents are set up in the sheet.
Thus, there will always be a force opposing the motion of the sheet. This braking force acts to dampen the oscillations.
Eddy current (since its a closed aluminium sheet) can also dissipate energy into the material as heat BY COE and are sources of energy losses. To reduce eddy currents, the bulk piece of metal is laminated
Graph of B and Emf induced over time
See LN
D13- Why a potential difference is set up between ends of the coil
The downward velocity, v of the rod varies with distance s fallen as given by v^2 = 2gs.
FRHR REMB THE FINGERS ALL DIFF FNS
Explain effects of amplitude and frequency of induced emf when
- ferrous core slowly introduced into the coil
- frequency of the current in the solenoid is increases, while maintaining the same amplitude of current
When a ferrous core is slowly introduced into
the solenoid, the core will be magnetized by the
external magnetic field of the solenoid. The
amplitude of the magnetic field experienced by the
search coil increases (due to the permeability), but the period with which it
varies is still the same. Hence, the amplitude of the
induced e.m.f. increases and there is no change in
the frequency with which the e.m.f. varies.
When the frequency is increased, the peak-to-peak change of the magnetic flux linkage
experienced by the coil happens in a shorter time interval. In other words, the rate of change of
flux linkage increases and thus the amplitude of the induced e.m.f. will increase. The frequency
with which the induced e.m.f. varies, is the same as the frequency with which the magnetic field
varies and hence the frequency with which the e.m.f. varies, will also increase.
explain how Lenz law is an example of the conservation of energy
Lenz’s Law states that the polarity of the induced e.m.f. is such that it tends to produce a current that creates
a magnetic flux to oppose the change in magnetic flux causing it. Consider the case of a magnet approaching a closed solenoid. The direction of induced current is always such as to (produce a magnetic force to) oppose the motion of the magnet (which was the cause of the
electromagnetic induction). Since the motion of the magnet is opposed, work must be done in order to
maintain the motion of the magnet. This mechanical work enables the conversion of energy into the electrical
energy of the current.
electromagnetic induction
a phenomenon in which an emf is induced when the magnetic flux linking a conductor changes and the magnitude of the induced EMF is equal to the rate of change of flux linkages.
explain why a bar magnet Y oscillates above a coil Q of alternating currents
Alternating current sets up alternating magnetic field in Q. Interaction of alternating field due Q and magnetic
field of magnet Y produces alternating force on Y, and Y is driven/forced to oscillate vertically.
explain dampening effects of a bar magnet above a coil (not due to eddy currents in the bar magnet itself no closed circuit)
Motion of X will be damped. Since there is a current through solenoids, which comes with joule heat in the
resistance of the solenoids, by principle of conservation of energy, some of the mechanical energy of system X as
well as the mechanical energy of system Y will be slowly dissipated as heating heat during oscillation. Eventually,
all mechanical energy will be lost as heat in the resistance of the solenoids.
explain the shit
ukuk
