Electromagnetic Induction - Video

Fill-in-the-blank flashcards covering the key concepts of electromagnetic induction, AC generation, transformers, and power transmission from the notes.

Magnetic flux in a coil is represented by .

Φ

Flux linkage is N times .

Φ

The total flux linking a coil of N turns is called the .

flux linkage

The magnitude of the induced emf is directly proportional to the rate of change of .

flux linkage

The direction of the induced emf is predicted by 's Law.

Lenz

An induced emf occurs only in a closed .

circuit

An induced emf is proportional to the rate of change of linkage.

flux

Induced emf can be generated by the relative movement between a coil and a .

magnet

Induction can also be produced by changing a field.

magnetic

In Faraday’s wire-cutting experiment, moving the wire results in a momentary deflection of the galvanometer, indicating an induced .

emf

When the magnet is moved into the solenoid, the galvanometer deflection indicates induced emf; when the magnet is withdrawn, the deflection is in the direction.

opposite

Faraday observed that induction can occur by the relative movement between a coil and a magnet or by changing a field.

magnetic

The two experiments where electromagnetic induction was first observed include wire-cutting and Faraday’s experiments.

experiments on induction

Flux is represented by the symbol .

Φ

Flux linkage is the total flux linking the coil and is equal to times Φ.

N

The rate of change of magnetic lines of force linked with the circuit determines the magnitude of the induced emf, i.e., rate of change of linkage.

flux

Lenz’s Law states that the induced current produces a magnetic effect that opposes the motion or change producing it; this is an expression of the of energy.

conservation

Faraday’s Law (magnitude) is not complete without Lenz’s Law to give the of the induced emf.

direction

An emf is induced whenever there is a change in flux linkage or flux being .

cut

Induced current flows only when the circuit is .

closed

The two key experiments of EM induction are cutting of flux and Faraday’s experiments.

wire

A simple form of an a.c. generator uses a rotating coil or a rotating .

magnet

The use of rings (or slip rings) allows continuous contact with external circuits in an AC generator.

slip

In an AC generator, the current reverses its direction every revolution.

half a

Two slip rings slide against fixed carbon brushes to allow connection to the external load; these connections are P and Q while X and Y refer to the .

rings

The graph of voltage output against time for a simple ac generator is a waveform.

sinusoidal

When the coil is horizontal, the rate at which it cuts magnetic lines is , giving a maximum emf.

greatest

When the coil is vertical, the rate of cutting magnetic lines is , giving a minimum emf.

least

Doubling the rotation speed of the coil doubles the maximum emf and the .

frequency

Doubling the number of turns per unit length of the coil doubles the maximum emf; this is because emf ∝ .

N

Doubling the magnetic field strength doubles the maximum emf; emf ∝ field strength and .

speed

A soft iron core in a transformer concentrates magnetic through the coil.

field lines

For an ideal transformer, input power equals power.

output

Vp/Vs = ; the voltage ratio equals the turns ratio.

Np/Ns

VpIp = VsIs expresses the conservation of in the transformer.

power

Power loss in cables due to Joule heating is given by P = .

I^2R

The use of a laminated core in transformers reduces energy losses due to currents.

eddy

Eddy currents are induced in the core by the changing magnetic field and cause heating.

joule

Leakage of magnetic field lines between primary and secondary coils leads to losses.

leakage

A core design that links the magnetic flux to the secondary coil more completely reduces magnetic field leakage; this is called reducing loss.

leakage

Hysteresis losses are due to continuous magnetisation and demagnetisation of the core; using a soft magnetic material reduces these losses, known as losses.

hysteresis

The efficiency of a transformer is improved by using a soft iron core and laminated to reduce eddy currents.

core

In a step‑up transformer, the secondary has more turns than the primary (Ns > Np). The voltage at the secondary is than the primary.

higher

In a step‑down transformer, the secondary has fewer turns than the primary (Ns < Np). The voltage at the secondary is than the primary.

lower

The turns ratio in a transformer is NP:NS; this turns ratio determines the of the transformer.

type (step-up or step-down)

A transformer changes voltage of an alternating current by having different numbers of turns in the coils.

primary and secondary

A transformer transfers energy through a magnetic between the windings.

link

In power transmission, power is transmitted at very high voltage to keep the current and reduce losses.

low

Power loss in transmission lines is minimized by increasing the transmission voltage and using thicker wires to reduce the line's resistance, R; this reduces Ploss proportional to I^2R and therefore reduces _ losses.

I^2R

Vout and Iout in a transmission line satisfy the relation Pout = _.

Vout Iout

The greater the value of V, the smaller the power loss in the cable, assuming the same transmitted power P, because I = P/V and P_loss ∝ I^2R.

increase voltage to reduce current

A high-voltage transmission system is more economical because it minimizes losses in cables.

Joule (I^2R)

The total resistance of a transmission line is R = ρL/A; this expression is a form of the law for resistivity.

Ohm's

Transmission at high voltage comes with a trade-off: insulation costs rise with increasing .

voltage

The term 'Energy Reset' in sustainability refers to a transition to sustainable energy sources and improvements in energy .

efficiency

The LTMS-PIP project facilitates import of hydropower from Laos, through Thailand and Malaysia, to Singapore via interconnectors; this is an example of regional energy .

integration

Phase 1 of LTMS-PIP allowed imports up to MW of renewable hydropower.

100

Phase 2 of LTMS-PIP aims to double imports to MW.

200

The Lao PDR–Thailand–Malaysia–Singapore Power Integration Project supports net-zero emissions goals in line with SDG 7 and SDG .

SDG 13

In a Faraday's induction experiment, when the magnet moved into the solenoid, the galvanometer showed a deflection due to a change in magnetic .

flux

In Faraday’s experiments, a stationary magnet in the solenoid produced deflection in the galvanometer.

no

Relative movement between a coil and a magnet can induce an emf; this is one way to produce electromagnetic .

induction

When the magnetic field changes, an emf is induced in a conductor; this is described by Faraday's of electromagnetic induction.

law

Lenz’s Law is a statement about the direction of induced current to oppose the change in .

flux

In a transformer, the primary coil is connected to an alternating current supply; this produces a continually changing magnetic field in the core that links to the coil.

secondary

The magnetic field is concentrated by the soft iron core which links to the secondary coil via the core.

iron

The ideal transformer follows Vp/Vs = Np/Ns and Ip/Is = Ns/Np; combining these gives VpIp = VsIs, i.e., power in equals power .

out

The graph of voltage output vs time for a simple AC generator is a waveform.

sinusoidal

In a simple AC generator, the coil’s rotation through 180° reverses the of the induced current.

direction

In the AC generator, slip rings X and Y connect to fixed carbon brushes P and Q so that the load sees an current.

alternating

Freeman’s right-hand rule (FRHR) helps deduce the direction of induced in a generator.

current

If the coil is at 0° (horizontal), the induced emf is at a(n) value.

maximum

If the coil is at 90° (vertical), the induced emf is at a(n) value.

minimum

The emf in an AC generator is produced by continual changes in magnetic field linked with the coil due to its rotation; this is an example of a(n) generator.

AC

The primary and secondary windings are wound on opposite sides of an iron core to form a(n) transformer.

mutual

In an ideal transformer, the total energy transferred from primary to secondary is governed by the equation VpIp = VsIs, showing energy _.

conservation

The no-load emf of an open circuit in a transformer is set up, but no current flows; this shows that an emf can exist without induced .

current

The transformer uses a core that concentrates magnetic fields to maximize coupling and minimize between windings.

leakage

Step-up transformers have a turn ratio greater than 1; therefore Vs > Vp provided the current is adjusted to satisfy power in = power out, i.e., Vs Is ≈ Vp Ip. This is a consequence of energy .

conservation

The formula for basic transformer turns ratio is Np:Ns, which equals the ratio of primary to secondary .

turns

The purpose of a laminated core is to minimize energy losses due to eddy .

currents

The core is laminated to limit circular paths of induced currents, thereby reducing losses.

eddy

In power transmission, engineers aim to transmit at high voltage to minimize current and reduce losses.

I^2R

The efficiency of a transformer is defined as Output Power divided by Input Power times percent.

100

The efficiency of a real transformer is less than 100% due to various losses.

parasitic

Interconnectors in LTMS-PIP are used to transfer electricity between countries; these enable regional energy .

integration

The energy that is transformed into electrical energy in hydropower plants hinges on the principle of electromagnetic .

induction

The magnetic flux Φ linking a coil is proportional to the number of field lines crossing the coil's cross-sectional .

area

Flux linkage is the product of the flux Φ and the number of turns N: NΦ; this is the total flux linked with the coil's N turns.

NΦ

If the magnetic field is not changing and the coil is not moved, Faraday’s law predicts there is no .

emf

A changing magnetic field induces a(n) emf, which can drive a current if the circuit is closed.

induced

The symbol for electromotive force in the notes is .

ε

In the Faraday–Lenz framework, the induced emf is the rate of change of linkage.

flux

Fleming’s right-hand rule is used to find the direction of the induced current in a(n) .

generator

In an AC generator, the coil’s rotation reverses the direction of current every half turn, producing an alternating current; this is achieved via a(n) rings arrangement.

slip

The energy change that occurs when a magnet is moved into a coil is converted from mechanical work to energy.

electrical

Lenz’s Law is a manifestation of the conservation principle.

energy

The magnetic flux through a coil is linked with N turns, producing a flux linkage given by N × .

Φ

The ideal transformer equations relate voltages and turns: Vp/Vs = .

Np/Ns

The ideal transformer equations relate currents and turns: Ip/Is = .

Ns/Np