Explore 1: Resistivity in Computing

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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: Resistivity in Computing
Electricity – Resistivity

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Explore 1 Objective
Discover how resistivity underpins computing.
(Logic gates are not directly on the specification)

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Golden Link
A an ipad from 2014 is
equivalent to a
supercomputer from what
year?
Answer in video link.
A. 1965
B. 1975
C. 1985
D. 1995
Moore’s law 3.00 min
SLIDE:
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Starter
How does this link to resistivity?
• Computers are built on transistors.
• They rely on semiconductors.
• To understand semiconductors you
need to understand resistivity.
• Think of way that computer
technology has changed in your
lifetime.
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Semiconductors
• Most things in nature fall on a
spectrum but we human like and
need categories to think.
• Semiconductors, as their name
suggests, fall between the two
extremes.
• Crucially, outside factors, like
temperature or an applied current,
can make them change from
insulators to conductors
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Band Gap
• In individual atom electrons
occupy very specific shells.
• When close together these
shells effectively combine to
form bands.
• The valence band holds its
electrons closely.
• The conduction band
electrons are free to move.
• How easy it to get from one
to the other determines
resistivity and categorisation.
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Transistor
• Transistor are tiny switches with no moving parts.
• There are billions in your house.
• Most devices rely on them: car, fridge, dishwasher
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+
+
+
+
+
How a Transistor Works
+
+
+
collector
1. Transistors are usually made of three
+
N
+
+
+
semiconductor layers.
2. When they are made electrons move to
the middle layer.
+
+
3. This works as a block – it has high resistivity.
P
+
+
+
+
+
+
4. Electrons are removed from the base to
+
base
attract electrons, so overcoming the block.
+
+
+
N
+
+
10
+
+
+
SLIDE:
The switch is closed.
6. Some electrons will flow to the base but
most will flow to the collector.
emitter
+
5. The switch is open.

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AND Gate
A
OR Gate
A
B
Q
0
0
0
0
1
0
1
1
0
0
1
1
1
1
1
1
1
A
B
Q
0
0
0
1
0
0
1
A
B
B
Q
Q
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Logic Gates to Adders
This video explains adding
Adding negative numbers is
subtraction.
Repeated adding is multiplication.
Repeated subtraction is division.
All computer operation are
combination of the above.
Adders 5.43 min
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Definitions
Term
Definition
Resistivity
A materials ability to allow current to flow
Semiconductor
A material that can act like an insulator or conductor
Transistor
Tiny switch that uses semiconductors
Logic gate
Combination of transistors
Adder
Combination of logic gates
Computer
Device that uses millions of adders
The Future of Artificial Intelligence 1.02 hrs
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Plenary
Why does is
graphene potential
so useful?
What is graphene? 3.53 min
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Explore 2: Exam Practice
Electricity – Resistivity

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Explore 2 Objective
Apply resistivity in an exam context
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Starter
Watch the video.
It sounds good but what are the
problems?
• Cost of manufacture
• Cost of drilling
• Impact of drilling
Using Graphene cables to ‘mine’
geothermal energy 2.41 min
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Explore Activity
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Plenary
Levitation on a Mobius strip is
fun but what practical
applications are there for
superconductivity?
Superconducting Quantum Levitation on
a Möbius Strip
Answer, quite a few:
2.49 min
the production of sensitive magnetometers based on SQUIDs (superconducting quantum interference devices)
fast digital circuits (including those based on Josephson junctions and rapid single flux quantum technology),
powerful superconducting electromagnets used in maglev trains, magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR)
machines, magnetic confinement fusion reactors (e.g. tokamaks), and the beam-steering and focusing magnets used in particle accelerators
low-loss power cables
RF and microwave filters (e.g., for mobile phone base stations, as well as military ultra-sensitive/selective receivers)
fast fault current limiters
high sensitivity particle detectors, including the transition edge sensor, the superconducting bolometer, the superconducting tunnel
junction detector, the kinetic inductance detector, and the superconducting nanowire single-photon detector
railgun and coilgun magnets
electric motors and generators[1]
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Explore 3: Practical
Electricity – Resistivity

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Explore 3 Objective
Carry out resistivity practical
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Starter
What do m and c stand for in y = mx + c?
m = gradient
c = intercept
SLIDE:
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Step 1: Measure the Diameter of the wire
Measure the diameter in
three places.
Calculate a mean.
Calculate the crosssectional area of the wire.
Code
SLIDE:
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Link

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Step 2: Gather the Data
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Step 3: Graph the Results & Calculate ρ
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Plenary
Why is obtaining a value from a gradient better than just calculating values in a table?
• Graphs allow us to see an overview of all the result easily.
• A line of best fit is a kind of visual averaging of the results.
• Anomalies are easy to sport. It allows to take a step to the right on the options below.
SLIDE:
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Explore 4: Exam Practice
Electricity – Resistivity – Week 13

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Explore 4 Objective
Apply ideas in an exam context
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Starter
How many seconds have there been since the
Big Bang (13.7 billion years)?
What volume, in cm 3 , of copper would
have that many free (valence) electrons?
t = 13.7 × 109 × 365 × 24 × 60 × 60
t = 4.32 × 1017 s
n = 8.47 × 10 22 cm -3
V = 4.32 × 10 17 ÷ 8.47 × 10 22
V = 0.0000051 cm3
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Q1
Derive the units for resistivity.
ρ = RA / l
Ω m 2 ÷ m = Ωm
SLIDE:
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Q2
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Q2
I = nqvA
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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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Plenary: MindMap
Add anything and everything to the mindmap!
Resistivity
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Lesson complete!
See you next lesson