Electromagnetism

Level 3 Physics Study!

using the __ grip rule, if you wrap your fingers around a _______, which is an _______, in the direction of _______ _______, then your thumb will point towards the _______ pole of the _______ field created

RH, coil, inductor, conventional current, north, magnetic

the _______ _______ passing through an area is equal to the _______ _______ _______ multiplied by the _______-_______ _______, given by Φ = BA⊥ = BA____θ

magnetic flux, magnetic field strength, cross-sectional area, cos

magnetic flux, Φ, is measured in _______, __

Webers, Wb

magnetic field strength, __, is measured in _______, __

B, Teslas, T

to induce magnetic flux, the cross-sectional area and magnetic field lines must be _______ to each other

perpendicular

when A is parallel to B, there is _______ (0/max) Φ induced

0

when A is perpendicular to B, there is _______ (0/max) Φ induced

max

a/an _______ _______, or p_______ _______, is induced when there is a/an _______ in magnetic flux through the _______

back emf, potential difference, change, conductor

the direction of the back emf is such that it produces a/an _______ (in a closed circuit) that has a/an _______ effect which _______ the change that caused it

current, magnetic, opposes

a change in _______ _______ can be caused by a rotating conductor; changing the strength of B; moving the conductor or the magnet in relation to each other; etc.

magnetic flux

faraday’s law states that the _______ _______ induced in a conductor is directly proportional to the rate of _______ of _______ _______ through the conductor

back emf, change, magnetic flux

lenz’s law states that the _______ of the back emf is such that it produces a current that has a/an _______ effect that _______ the change that caused it

direction, magnetic, opposes

lenz’s law is due to _______ of _______

conservation, energy

according to lenz’s law, E_______ is transferred to E_______, as a back emf and current is induced

kinetic, electrical

for a coil of wire, ε = -__ ∆Φ/∆t

N

using faraday’s law for back emf induced in a coil of wire, __, or the _______ of _______, must be taken into account

N, number, turns

ε = b_______ _______ = i_______ _______ = p_______ _______

back emf, induced voltage, potential difference

for a coil of wire, each turn experiences _______ (the same / a different) change in magnetic flux, causing ε to be induced

the same

_______ currents in a conductor are magnetically induced currents which oppose the change in magnetic flux

eddy

eddy currents _______ energy as _______, which is not a good thing in real life!

dissipate, heat

are eddy currents linear?

no

eddy currents produce a magnetic field which _______ the relative motion; eg, south - _______

opposes, south

a solid piece of metal will produce a single _______er eddy current which opposes the change in magnetic flux

large

a _______ piece of metal with many slits in it will produce many _______er eddy currents which are _______, so there is no eddy current across the whole conductor

laminated, small, disconnected

is the eddy current produced by a solid metal conductor, or a laminated metal conductor, negligible in effect?

laminated metal conductor

1. there is relative _______ between the conductor and magnet

2. causes a _______ in the _______ _______ in the conductor

3. induces a _______ _______, or _______, across the conductor

4. if the conductor is a _______ circuit, a _______ will be drawn

5. the _______ flows in a direction that has a _______ effect which _______ the change in _______ _______

6. due to _______ of _______

motion, change, magnetic flux, back emf, voltage, closed, current, current, magnetic, opposes, magnetic flux, conservation, energy

a coil of wire is a/an _______

inductor

an inductor has a value for _______, __

self-inductance, L

when the switch to the power supply is closed, is the circuit completed, or is the inductor charged?

circuit completed

an ideal inductor has _______ _______

no resistance

an inductor with resistance may be drawn with a _______ next to it

resistor

when the circuit is completed, current flows through the inductor to create a _______ _______ and cause a _______ in _______ _______, inducing a _______ _______ which opposes the terminals of the power supply

magnetic field, change, magnetic flux, back emf

the instantaneous back emf induced in the inductor when a switch is closed is _______ and _______ to the _______ of the power supply, due to _______ of _______ according to Kirchhoff’s laws

equal, opposite, voltage, conservation, energy

as the rate of change of the magnetic flux _______ over time after the switch is closed, the _______ _______ also _______

decreases, back emf, decreases

5τ after the switch is closed, the back emf has fallen to a _______ value, and _______ flows through circuit as normal

negligible, current

when the circuit is _______, the magnetic field around the inductor _______. since the rate of change in magnetic flux from something to nothing is huge, the _______ _______ is very large. if the _______ taken to break the circuit is _______ enough, the _______ _______ can be larger than the original _______ _______, as the incomplete circuit no longer obeys _______ of _______ due to Kirchhoff’s laws

broken, collapses, back emf, time, short, back emf, supply voltage, conservation, energy

the _______ _______ can exceed the supply voltage when the circuit is _______

back emf, broken

the _______ in magnetic flux begins at _______ when the circuit is completed then _______ (increases/decreases) exponentially (0/max)

change, max, decreases

the current flowing through a circuit begins at _______ when the circuit is completed due to a large _______ _______ which opposes the _______ _______ of the power supply, then _______ (increases/decreases) exponentially

0, back emf, terminal voltage, increases

energy is stored in an inductor’s _______ field

magnetic

energy is stored in a capacitor’s _______ field

electric

self-inductance is measured in _______, __

Henries, H

τ is proportional to _______ for inductors

self-inductance

τ is inversely proportional to _______ for inductors

resistance

V_L, which is the _______ _______ induced in a/an _______, _______ exponentially as the circuit is completed

back emf, inductor, decreases

the graph of V_L against time when a circuit it broken is _______ to that of when the circuit is made, beginning from _______ and changing exponentially to _______ (max / 0 / -max)

opposite, -max, 0

since τ = L/R, when the resistance of a circuit _______ when the circuit is broken, the time constant will _______ (_______ stays the same)

increases, decrease, self-inductance

V_resistor, which is the _______ across another component in the circuit with resistance, _______ exponentially as the circuit is completed, when plotted against time

voltage, increases

V_L and V_resistor are _______ proportional

inversely

the graph of I against time when a circuit is completed _______ exponentially, as the _______ in _______ _______ falls and the _______ _______ induced also decreases

increases, change, magnetic flux, back emf

though there is no formula for an inductor’s construction, self-inductance, L, depends on:

• the number of _______ in the coil

• if the inductor has a (soft iron) _______, which will _______ L

• the _______ of the inductor

turns, core, increase, size

_______ is when the changing magnetic flux through the inductor due to the changing _______ supplied through it induces a _______ that opposes the change in _______

self-inductance, current, voltage, current

combining faraday’s law with self inductance:

ε = -∆Φ/∆t and ε = -L ∆I/∆t

therefore, ∆Φ = _____

L∆I

in a capacitor, energy stored is E_p = ½CV²; in an inductor, energy stored becomes E_p = ½ __ x __²

L, I

for energy stored in an inductor, calculated using E_p = ½LI²,

• E_p = energy stored in _______ field, __

• L = _______, __

• I = _______, __

magnetic, J, self-inductance, H, current, A

transformers cause a step up or down in _______

voltage

for a transformer, a/an _______ _______ (from an AC supply or varying DC from an electric generator component) is put across the _______ coil, which produces a changing _______ and therefore a varying _______ _______

alternating voltage, primary, current, magnetic flux

for a transformer, the changing magnetic flux from the _______ coil _______ through the soft iron _______ to the _______ coil, known as _______ _______

primary, links, core, secondary, flux linkage

does current flow through the soft iron core in a transformer?

no

does flux linkage between the primary and secondary coil require current to flow between them?

no

the changing magnetic flux in the _______ coil induces a _______ _______

secondary, back emf

the ratio of _______ between the two coils of a transformer is the same as the ratio of the numbers of _______ in each coil

V_p / V_s = N_p / N_s

voltages, turns

if the secondary coil of a transformer has more turns, the voltage will be _______ (stepped up / stepped down)

stepped up

as V_s increases (stepped up from V_p), ___s decreases, due to _______ of _______

I, conservation, energy

since P = IV, and V = IR, P = I²/R, so a smaller current drawn from the secondary coil in a transformer (when V_s is stepped up) causes less _______ to be dissipated as heat for the same _______, causing higher _______

energy, resistance, efficiency

ε = -M ∆I_p/∆t, where ε is the _______ induced in the _______ coil and M is the _______ _______

voltage, secondary, mutual inductance

mutual inductance is how well the _______ in _______ in the primary coil _______ with the secondary coil

change, flux, links

an ideal transformer has 100% efficiency with no energy loss, so M = __, but _______ _______ cause heating in the soft iron _______, which means _______ is lost

1, eddy currents, core, energy

_______ of a transformer = P_s / P_p

efficiency

for transformers, eddy currents are _______ currents induced in the soft iron _______ due to a _______ _______ induced by the change in _______ _______, which dissipates _______ due to _______

transient, core, back emf, magnetic flux, energy, heating

in AC currents, the _______ (or voltage) from a generator or mains supply varies _______

current, sinusoidally

a DC supply has a _______ direction and size of voltage

constant

a/an _______ _______ can create a/an _______ _______ from a DC supply which changes size and direction

electric generator, alternating voltage

the current drawn from an AC supply alternates in _____ and _______

size, direction

circuits with only _______ components can operate from either AC or DC supplies

resistive

RMS means _______ _______ _______

root mean square

RMS is the current value that is equivalent to DC, and would produce the same _______ (heating effect) dissipated for a resistive load, R

power

AC and DC supplies can be thought of as equivalent if they deliver the same _______, or RMS, to a circuit

power

V_{____} = V_max / √2 and I_{____} = I_max / √2

RMS

an AC current will cause the voltage and current through a resistor to vary sinusoidally / stay the same

vary sinusoidally

V_{________} = V_maxsin(ωt)

resistor

I_{________} = I_maxsin(ωt)

resistor

for a capacitor in AC, the _______ must flow first so that _______ can build up, causing a _______ across the plates; therefore, _______ leads _______ by 90°

current, charge, voltage, current, voltage

for a capacitor in AC, the _______ is at a maximum when there is no current flowing, as there is maximum _______ built up on either plate

voltage, charge

the _______ of a capacitor is how much is opposes the flow of _______

reactance, current

increasing the capacitance _______ the reactance

decreases

increasing the frequency _______ the capacitance

decreases

for the _______ of a _______ in AC, X_c = 1 / ωC, where…

• ω = _______, __

• C = _______, __

reactance, capacitor, angular frequency, rad/s, capacitance, F

a capacitor with a low capacitance and a low frequency has a _______ (high/low) reactance

high

a capacitor in a DC circuit essentially has __ Hz angular frequency, so the reactance is _______ (high/low) and it will greatly oppose the flow of _______

0, high, current

voltage is proportional to the _______ on the capacitor plates

charge

V_suppy² = V_resistor² + V_capacitor² - must be added as _______, using _______ conservation of _______ law

vectors, kirchhoff’s, energy

the phase difference between V_resistor and V_supply can be calculated as an angle using _______ addition, with the knowledge that V_______ and V_capacitor are 90° out of phase, with V_______ leading

vector, resistor, resistor

X_L = ωL, where…

• X_L = _______ of the _______

• ω = _______, __

• L = _______, __

reactance, inductor, angular frequency, rad/s, inductance, H

the reactance is the _______ _______ of a graph plotted between V and I

gradient constant

_______ is a measure of how much an inductor impedes the flow of _______, due to an induced _______ opposing the change in _______, and therefore the change in _______ _______

reactance, current, voltage, current, magnetic flux

increasing the rate of change of current _______ X_L 

increases

increasing the inductance of the inductor _______ X_L

increases

an inductor in AC with a high rate of change of current through it and a high inductance has a _______ reactance

high

a higher X_L causes greater _______ across the inductor

voltage