Post on 13-Dec-2015
Electromagnetic Induction
What is electromagnetic induction?
It is the production of an emf by a changing magnetic field.
Faradays Law of electromagnetic inductionThe induced emf in a conductor is directly proportional to the rate of change of magnetic flux through the conductor.
This is the principle behind the electric generator or dynamo.
What is magnetic flux?
Magnetic flux φ = B X A
The unit of magnetic flux is the weber.
To demonstrate electromagnetic induction (or Faradays Law)
Mutual Induction
Mutual induction occur when the changing magnetic field surrounding one coil causes an emf to be induced in a nearby coil.
The transformer is a practical application of this principle
Step downtransformer
The Transformer Equation
OUT
IN
S
P
V
V
N
N
NP = Number of turns in the primaryNs = Number of turns in the secondaryVin = Voltage inVout = Voltage out
Energy Losses in the transformer
Ideally
Power in = Power out
(VI)IN=(VI)OUT
Energy Losses in the transformer
To reduce energy losses.• Laminate the core-this reduces currents
induced in the core• The low voltage coil carries the greatest
current so it should be made of thick wire which has low resistance.
• The core is made of iron which is easy to magnetise and demagnetise.
Self Induction
The production of an emf in a coil due to its own changing magnetic field.To demonstrate self inductionThe neon lamp flashes when the switch is opened as the rapidly collapsing magnetic field induces a large emf in the coil. (self induction)
Alternating Current
This trace may be shown using an oscilloscope.
RMS Values of AC
20II rms
20VVrms
When calculating power with AC always use the rms values not the peak values.
AC and CapacitorsA charged capacitor blocks DC but conducts AC.
AC and inductorsInductors and AC
Inductors act as resistors to AC.If the power source is DC the current through a coil is greater than if the
power source is AC. This is due to the induced emf that opposes the applied emf.
Uses of inductors1.Dimming stage lighting2.Tuning radios