Download Chapter 6 - Topic 11 - Electromagnetic induction – AHL.

Chapter 6 - Topic 11 - Electromagnetic induction – AHL.
Essential idea: The majority of electricity generated throughout the world is generated by machines that were designed to operate using the principles of electromagnetic induction.
11.1 – Electromagnetic induction
Nature of science 1.8
Experimentation: In 1831 Michael Faraday, using primitive equipment, observed a minute pulse of current in one coil of wire only when the current in a second coil of wire was
switched on or off but nothing while a constant current was established. Faraday’s observation of these small transient currents led him to perform experiments that led to his law of
electromagnetic induction.
Hamper – having discovered that a changing current in one coil causes a current in a second unconnected coil, Faraday could have designed a simple electrical generator without any
understanding of how it works. By performing experiments, changing different variables, Faraday went far beyond initial discovery to formulate his law of electromagnetic induction.
1
U
Electromotive force (emf)
A
Describing (Describe) the production of an induced emf by a changing magnetic flux and within a uniform magnetic field
2
U
Magnetic flux and magnetic flux linkage
3
U
Faraday’s law of induction
A
G
4
DB
Φ = BAcosθ
Solving (Solve) problems involving magnetic flux, magnetic flux linkage and Faraday’s law
DB
ε = −NΔΦ/Δt
Quantitative treatments will be expected for straight conductors moving at right angles to magnetic fields and rectangular
coils moving in and out of fields and rotating in fields
DB
ε = Bvℓ
U
Lenz’s law
A
Explainin (Explain) Lenz’s law through the conservation of energy
G
Qualitative treatments only will be expected for fixed coils in a changing magnetic field and ac generators
ε = BvℓN
Essential idea: Generation and transmission of alternating current (ac) electricity has transformed the world.
11.2 – Power generation and transmission
Nature of science 3.5
Bias: In the late 19th century Edison was a proponent of direct current electrical energy transmission while Westinghouse and Tesla favoured alternating current transmission. The
so-called “battle of currents” had a significant impact on today’s society.
Hamper – the invention of the generator made it possible to deliver energy to homes and factories using a network of cables. Generators can be made to deliver either a current that always
travels in one direction (DC) or one with changing direction (AC). In the early days of electrification there was much competition between the producers of different generators who both wanted
their system to be adopted. One advantage of AC is that it is relatively simple to step the voltage up and down using a transformer. Supporters of DC saw this a danger and demonstrated it
publicly by electrocuting an elephant called Topsy.
1
U
Alternating current (ac) generators
A
Explaining (Explain) the operation of a basic ac generator, including the effect of changing the generator frequency
DB
Vrms=V0/√2
Irms=I0/√2
2
U
Average power and root mean square (rms) values of current and voltage
A
Solving (Solve) problems involving the average power in an ac circuit
U
Transformers
A
Solving (Solve) problems involving step-up and step-down transformers
Describing (Describe) the use of transformers in ac electrical power distribution
Calculations will be restricted to ideal transformers but students should be aware of some of the reasons why real
transformers are not ideal (for example: flux leakage, joule heating, eddy current heating, magnetic hysteresis)
R=V0/I0=Vrms/Irms
Pmax=I0V0
3
G
4
5
U
Diode bridges
A
Investigating (Investigate) a diode bridge rectification circuit experimentally
Qualitatively describing the effect of adding a capacitor to a diode bridge rectification circuit
U
Half-wave and full-wave rectification
A
Proof of the relationship between the peak and rms values will not be expected
1
𝑃 = 𝐼0 𝑉0
2
DB
εp /εs = Np /Ns = Is /Ip
Essential idea: Capacitors can be used to store electrical energy for later use.
11.3 – Capacitance
Nature of science 3.1
Relationships: Examples of exponential growth and decay pervade the whole of science. It is a clear example of the way that scientists use mathematics to model reality. This topic
can be used to create links between physics topics but also to uses in chemistry, biology, medicine and economics.
Hamper – the rate at which charge flows off a capacitor is proportional to the amount of charge on the capacitor. This leads to an exponential relationship between the charge and time. This is
the first time we have come across an exponential relationship but it won’t be the last.
1
U
Capacitance
A
Solving problems involving parallel-plate capacitors
Determining the energy stored in a charged capacitor
DB
C = qV
C = εA/d
E = ½ CV2
2
3
G
Only single parallel-plate capacitors providing a uniform electric field, in series with a load, need to be considered (edge effect will be
neglected)
U
Dielectric materials
A
Describing the effect of different dielectric materials on capacitance
U
Capacitors in series and paralle
A
Investigating combinations of capacitors in series or parallel circuits
DB
Cparallel = C1 + C2 + ⋯
1
𝐶𝑠𝑒𝑟𝑖𝑒𝑠
4
Resistor-capacitor (RC) series circuits
DB
A
U
Solving problems involving the discharge of a capacitor through a fixed resistor
Describing the nature of the exponential discharge of a capacitor
Problems involving the discharge of capacitors through fixed resistors need to be treated both graphically and algebraically
Problems involving the charging of a capacitor will only be treated graphically
Time constant
DB q = q0 e −t/τ
A
Solving problems involving the time constant of an RC circuit for charge, voltage and current
G
5
τ = RC
U
I = I0 e −t/τ
V = V0 e −t/τ
G
Derivation of the charge, voltage and current equations as a function of time is not required
=
1
1
+ +⋯
𝐶1 𝐶2