Analogies for electricity. Electricity – fundamentals

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Recording Notice
This lesson is
being recorded

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King’s Interhigh Logo

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Explore 1: Analogies for Electricity
Electricity – Fundamentals

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Objectives

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Starter
Watch the clip.
Explain how it could be a model for
an electrical circuit.
Try and think of 4 elements.
Playful Penguin Race 0.32 min
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Stairs:
Cell
Penguins:
Electrons
GPE:
Electrical Energy
Friction:
Resistance

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Starter: Link to Real Circuit
Energy in
Energy out
As the marbles literally drop they lose GPE.
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By analogy we talk about a ‘voltage drop’.

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Waterfall Sim
This is a bit more complicated than
the penguins. Sign up required.
Explain the similarities and
differences.
Similarity:
• Height represent electrical
energy
Differences:
• There are parallel setups
• Component are modelled
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Chain
How is a bicycle chain like a circuit.
How is better than the water analogy?
The rider: cell
Chain: current
Back wheel: component
One advantage is the chain is
definitely not used up or discarded like
the water.
Also, if the load changes the rider
feels it instantly.
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9.

Cash Point and Shop Analogy
This analogy captures the idea of
voltage nicely.
If you nosily look in someone’s wallet
before and after they go in a shop,
you can work out how much they
spent.
This is exactly what a voltmeter does.
Remember voltage is Joules per
Coulomb.
In this analogy it would be £ per
£100
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£80
person.

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Analogy Summary
All of the analogies we have looked at have pros and cons.
Try and get something from all of the them.
None is exactly like the real thing.
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Calculation 1
What is resistance if
current is 68.3 mA and
Voltage is 4.1 kV?
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Step
Detail
Identify
R = ? V = 4.1 kV I = 68.3 mA
Match
V = 4,100 V
I = 0.0683 A
Formula
V = IR
Arrange
R=V÷I
Substitute
R = 4,100 ÷ 0.0683
Total
R = 60,029 Ω = 60 kΩ

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Calculation 2
What is current if time is 3 days
Step
Detail
and charge is 23.6 kC?
Identify
I = ? t = 3 days Q = 23.6 kC
Match
t = 3 × 24 × 3600 = 259,200 s
Q = 23,600 C
Formula
Q = It
Arrange
I=Q÷t
Substitute
I = 23,600 ÷ 259,200
Total
I = 0.09 A
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Calculation 3
7.8 C does 8,800 J of work.
What must the voltage have
been?
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Step
Detail
Identify
V = ? Q = 7.8 C W = 8,800 J
Match
-
Formula
W = QV
Arrange
V=W÷Q
Substitute
V = 8,800 ÷ 7.8
Total
V = 1128.21 ≈ 1100 V (2sf)

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Voltage vs Voltage Across
Term
Definition
Voltage
Push in a circuit
Joules per Coulomb
Energy per electron
Voltage across
(some component)
Potential Electrical Energy Difference between two
points
aka Potential Difference
aka P.D.
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Plenary
Try and write your own summary for
the topic so far.
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Objectives
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Explore 2: Exam Practice
Electricity – Fundamentals

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Objectives

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Starter
Why was the Coulomb
invented?
Because electrons are
ridiculously small and
therefore awkwardly
numerous.
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Q1
A
B
C
D
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0.03 C
2C
18 C
1080 C

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Q1
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Q2
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Q2
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Q3
A
B
C
D
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0.75 C
45 C
750 C
45,000 C

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Q3
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Q4
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Q4
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Q5
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Q5
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Q6
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Q6
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Plenary: Taboo
Play Taboo with any word from the learning objectives.
Describe the word without using any of the others in the learning objectives.
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Objectives
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Explore 3: Practical
Electricity – Fundamentals

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Objectives
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Starter
List the as many quantities as you can related to electricity including their
symbols and units.
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CONCEPT
NAME
UNIT
Ability to do
Energy (E)
Joule (J)
Change
Time (t)
Second (s)
Electrons
Charge (Q)
Coulomb (C)
Flow
Current (I)
Amp (A or C/s)
Push
Voltage (V)
Volt (V or J/C)
Energy Rate
Power (P)
Watt (W or J/s)
Obstacle
Resistance (R)
Ohm (Ω or V/A)

37.

Practical: Max Power
1. Build circuit
2. Set internal
resistance* to 5 Ω
6. Calculate power
3. Adjust
external
resistance
4. Record
voltage and
current
5. Predict when
the power will be
greatest & why
7. Graph power
against resistance
*we will return to internal resistance in week 13, for the moment just think of it as making the circuit more realistic.
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Result
As resistance increases the external resistor gets a greater share of voltage.
However, more resistance means less current.
There is a trade off between the two so the graph peaks.
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Plenary
Which statement(s) are correct?
A. Voltage is proportional to resistance
B. Voltage is inversely proportional to current
C. Current is proportional to voltage
D. Current is proportional to resistance
E. Current is inversely proportional to resistance
Correct answers: C and E
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Objectives
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Explore 4: Exam Practice
Electricity – Fundamentals

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Explore 4 Objective
Apply ideas in an exam context
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43.

Starter
Calculate the mass of electrons in the human body.
Assume
Mass of 70 kg
To a first order approximation humans are made of oxygen
All atoms are the most common isotope: oxygen-16
Use the data sheet to find the values of e m and u.
Mass of one O atom
= 1.66 × 10 -27 kg × 16 = 2.66 × 10 -26 kg
Number of O atoms
= 70 ÷ 2.66 × 10 -26 = 2.64 × 10 27
Electrons per O atom
= 8
Total electrons
= 8 × 2.64 × 10 27 = 2.12 × 10 28
Total electron mass
= 2.12 × 10 28 × 9.11 × 10 -31 kg = 0.019 kg = 19 g
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Q1
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Q1
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Q2
The photograph shows a piece of apparatus in which
a mains light bulb and a torch bulb are both
connected to the mains.
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Q2
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Q2
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Q2
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Q2
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Q2
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Q2
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Q3
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Q3
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Q4
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Q4
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Q5
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Q5
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59.

Plenary Taboo
• Play Taboo with any word from the learning objectives.
• Describe the word without using any of the others in the learning objectives.
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60.

Lesson complete!
See you next lesson