Electromagnetic Induction & Alternating Current Flashcards
Electromagnetic induction
The εmf produced across a conductor exposed to a varying magnetic field
Fleming’s right hand rule
Predicts the direction that an induced current flows, e.g. when a wire is moved through the magnetic field between two magnets
Fleming’s left hand rule
Predicts the the direction of the force on a current-carrying conductor in a magnetic field, e.g. it predicts the direction of rotation of an electric motor
What conclusions did Faraday come to when experimenting with magnetic fields and electromagnetic induction?
- when a conductor is moved through a magnetic field, the magnitude of the induced εmf is equal to the rate at which magnetic flux is cut through by the conductor
- when a magnet is moved near a coil, the magnitude of the induced εmf is equal to the rate of change of flux multiplied by number of turns in the coil, the rate of change of flux linkage
Faraday’ law
When the magnetic flux linking a circuit changed, and εmf is induced in the circuit proportional to the rate of change of the flux linkage. The equation linking εmf, E, to flux linkage is
E = NΔΦ/Δt
Lenz’s law
The direction of an induced current opposes the change of magnetic flux that produces it
Eddy currents
Finish
When a current is induced due to a change in magnetic field, where does the energy to drive this current come from?
It comes from the work done in moving the conductor or magnetic field against the repulsive force created from the induced current. Lenz’s law
Generator
In the context of electromagnetic induction: It consists of a rotating coil within a magnetic field and is used to generate an alternating current by electromagnetic induction
Peak voltage
The maximum value for an alternating εmf and so is the highest amplitude value of the εmf
Peak-to-peak voltage
The difference between the maximum and minimum values for an alternating εmf, twice the amplitude of the εmf
What does the equation
ε = BAN ωsinωt describe?
How the εmf induced in a coil rotating uniformly in a uniform magnetic field varies with time
Root mean square (rms)
The value of an ac current or potential difference that is equal to the dc value that would lead to the same power being dissipated in a resistor
The average power dissipated in a resistor by an ac current is
P(av) = I²(rms)R = V(rms)I(rms)
The resistance in a circuit produced by an ac current is
R = V(rms)/I(rms) = Vo/Io
Oscilloscope
A cathode ray oscilloscope is used for measuring dc and ac voltage, measuring time intervals and frequencies and also displaying alternating waveforms
Time base
The control on an oscilloscope that determines the speed at which the electron beam moves horizontally across the screen
How can you measure the ac frequency from an oscilloscope when it’s input control is set to AC, and a signal generator is set to its some function and connect to the y-input?
Time period = number of divisions for one cycle x time base setting
How can you calculate the εmf of a battery connected to an oscilloscope set to DC?
ε = number of divisions (where line rests) x y-gain (number of V/div)
An oscilloscope screen is an
Adjustable voltage versus time graph
The sensitivity of the vertical axis on an oscilloscope screen can be adjusted using
the y-gain control
The sensitivity of the horizontal axis on an oscilloscope screen can be adjusted using
the time base control
