Electromagnetic induction Flashcards
What is electromagnetic induction?
When an e.m.f is induced in a closed circuit conductor due to it moving through a magnetic field.
Give examples of conductors that can exhibit electromagnetic induction.
A flat coil or a solenoid.
When does electromagnetic induction occur?
When a conductor cuts through magnetic field lines.
What determines the amount of e.m.f induced?
The magnetic flux.
What is magnetic flux?
The total magnetic field that passes through a given area.
When is magnetic flux a maximum?
When magnetic field lines are perpendicular to the plane of the area.
When is magnetic flux zero?
When magnetic field lines are parallel to the plane of the area.
Define magnetic flux.
Product of magnetic flux density and the cross-sectional area perpendicular to the direction of the magnetic flux density.
What is the symbol for magnetic flux?
Φ (phi).
What is the unit for magnetic flux?
Weber (Wb).
State the equation for magnetic flux.
Φ = B × A
What do the variables in Φ = B × A represent?
Φ = magnetic flux (Wb), B = magnetic flux density (T), A = area (m²).
Draw and explain the graph of magnetic flux vs angle for a rotating window.
It is provided in the document.
What is magnetic flux linkage?
The product of the magnetic flux and the number of turns of the coil.
State the equation for magnetic flux linkage.
Flux linkage = ΦN = BAN
What are the units of magnetic flux linkage?
Weber-turns (Wb turns).
State the equation for flux through a rotating rectangular coil.
Φ = B × A × cos(θ)
What do the variables in Φ = B × A × cos(θ) represent?
θ = angle between magnetic field and the normal to the area.
When is magnetic flux maximum in a rotating coil?
When θ = 0°, i.e., field is perpendicular to the plane.
When is magnetic flux zero in a rotating coil?
When θ = 90°, i.e., field is parallel to the plane.
What causes an induced e.m.f in a circuit?
A changing magnetic flux linkage.
State the modified flux linkage equation for rotating coil with N turns.
ΦN = BAN cos(θ)
Define electromagnetic induction in principle.
Process in which an e.m.f is induced due to changes in magnetic flux.
State two ways electromagnetic induction occurs.
1) Conductor cuts through magnetic field. 2) Direction of magnetic field through coil changes.
List uses of electromagnetic induction.
Generators and transformers.
Describe the setup for moving magnet through a coil to induce e.m.f.
A bar magnet moved through a coil connected to a voltmeter.
State the effect of increasing speed of the magnet.
Increases the magnitude of the induced e.m.f.
Draw and explain the graph of e.m.f vs time when moving magnet through coil.
It is provided in the document.
Describe what happens when moving a wire through a magnetic field.
An e.m.f is induced if it cuts through field lines.
State factors that increase induced e.m.f in a wire.
Increase length, speed, or magnetic field strength.
State Faraday’s Law.
Induced e.m.f is proportional to the rate of change of magnetic flux linkage.
State Lenz’s Law.
Induced e.m.f opposes the change causing it.
Give the equation for Faraday’s Law.
ε = -N × ΔΦ / Δt
What do the variables in Faraday’s law equation represent?
ε = induced e.m.f (V), N = number of turns, ΔΦ = change in flux (Wb), Δt = time (s).
State the e.m.f equation for a straight conductor moving through a magnetic field.
ε = B × L × v
What variables are used in ε = B × L × v?
B = magnetic flux density (T), L = length (m), v = velocity (m/s).
State the flux linkage equation for a rotating coil using angular velocity.
NΦ = BAN cos(ωt)
State the e.m.f equation using angular velocity.
ε = BANω sin(ωt)
What does ω represent?
Angular speed (rad/s).
What is the phase difference between flux linkage and induced e.m.f in a rotating coil?
They are 90° out of phase.
Draw and explain the sinusoidal graph of e.m.f and flux linkage.
It is provided in the document.
What is an alternating current (a.c)?
A current which periodically varies between a positive to a negative value with time.
What does it mean that the direction of an alternating current varies every half cycle?
It means the direction of flow of current changes after every half cycle.
Describe the variation of current or p.d. with time for a.c.
It can be described as a sine curve (sinusoidal).
What motion do electrons undergo in a wire carrying a.c?
They move back and forth with simple harmonic motion.
State the relationship between time period T and frequency f for a.c.
f = 1 / T
Define peak current (I0) or peak voltage (V0).
The maximum value of the alternating current or voltage.
How can peak current or voltage be determined?
From the amplitude of a current-time or voltage-time graph.
How is peak voltage V0 calculated from peak-to-peak voltage?
V0 = peak-to-peak voltage ÷ 2
Draw and explain a graph of alternating current against time showing the time period, peak current and peak-to-peak current.
It is provided in the document.
Define rms current (Irms).
The square root of the mean of the squares of all the values of the current in one cycle, or the equivalent direct current that produces the same power.
State the equation for rms current.
Irms = I0 / √2
Define rms voltage (Vrms).
The square root of the mean of the squares of all the values of the voltage in one cycle, or the equivalent dc voltage that produces the same power.
State the equation for rms voltage.
Vrms = V0 / √2
What is the relationship between rms and peak values?
Rms value is approximately 0.707 × the peak value.
What is the average power of a supply?
Average power = Irms × Vrms
Explain why mains electricity is supplied as a.c.
Because it allows the use of transformers to reduce energy losses in transmission.
What is the UK mains electricity specification?
230 V at 50 Hz (rms value).
Which devices use mains a.c. directly?
Lamps, heaters, cookers, and devices with large electric motors.
Which devices convert a.c. to d.c. using transformers?
Televisions, computers, games consoles.
What is a Cathode-Ray Oscilloscope (CRO) used for?
To display, measure and analyse waveforms of electrical circuits.
Draw and explain a diagram of an oscilloscope showing wavelength and time-base setting.
It is provided in the document.
What do the x-axis and y-axis represent on a CRO?
X-axis: time, Y-axis: voltage (y-gain).
State the formula to calculate frequency from time period.
f = 1 / T
What is the transformer equation?
Vs / Vp = Ns / Np
What is the ideal transformer power equation?
Ip × Vp = Is × Vs
What is the efficiency formula for a transformer?
Efficiency = Power out / Power in
How can eddy currents be reduced?
By laminating the core with insulated layers.
What causes inefficiencies in transformers?
Resistance in wires, eddy currents, magnetic hysteresis, poor insulation.
How can energy loss be reduced in transformers?
Laminated cores, thick wires, soft iron, linking all magnetic flux.
What equation is used for power loss in transmission lines?
P = I²R
Explain how step-up and step-down transformers reduce energy loss.
Step-up increases voltage and decreases current, reducing heat loss; step-down adjusts voltage for home use.
