SLIDE 1
Welcome back! Please fi ll out a name tent with whatever you want us - - PowerPoint PPT Presentation
Welcome back! Please fi ll out a name tent with whatever you want us - - PowerPoint PPT Presentation
Welcome back! Please fi ll out a name tent with whatever you want us to call you. EN 1-24: Engineering in the Kitchen Steven Bell 14 September 2020 Quick review of last time Is it possible to have a voltage without a current? Respond at
SLIDE 2
SLIDE 3
Quick review of last time
Is it possible to have a voltage without a current? Respond at pollev.com/stevenbell
SLIDE 4
Quick review of last time
Is it possible to have a voltage without a current? Respond at pollev.com/stevenbell Is it possible to have a current without a voltage?
SLIDE 5
By the end of class today, you should be able to:
Explain what resistance is Use Ohm's law to calculate V/I/R Explain what power is, and how it's different from energy Use Watt's law to calculate power
SLIDE 6
From the fantastic engineering/woodworking site woodgears.ca
Marble-track resistor
SLIDE 7
R is the resistance, measured in Ohms
I = V R
For a resistor (and only a resistor):
Ohm's Law
Represented with the schematic symbol:
SLIDE 8
WARNING WARNING WARNING!
Not everything behaves like a resistor. For example: Diodes (and light-emitting diodes, LEDs) Capacitors and inductors, which store energy Don't just blindly apply Ohm's law! Batteries
SLIDE 9
What is the current i?
5V 1kΩ
i
SLIDE 10
Let's measure some more interesting things.
SLIDE 11
Let's talk about safety
Electricity can kill you.
[citation needed]
But how? And is it the voltage or current that's dangerous?
SLIDE 12
10 s 5 s 2 s 1 s 500 ms 200 ms 100 ms 50 ms 20 ms 10 ms 100 µA 200 µA 500 µA 1 mA 2 mA 5 mA 10 mA 20 mA 50 mA 100 mA 200 mA 500 mA 1 A 2 A 5 A 10 A
T I
AC-1 AC-2 AC-3 AC-4 AC-4 AC-4.1 AC-4.2 AC-4.3
Wikipedia - Electrical injury
SLIDE 13
Ok, so what voltage is dangerous?
A phone charges at 1A or more, so why isn't that dangerous? (Or is it?)
SLIDE 14
Intermission: Interview your partner
I'll be coming around to take pictures
SLIDE 15
Intermission: Interview your partner
Who is from the furthest away? Who has the largest / most interesting pet? Who has the most siblings? Who has an interesting hobby?
SLIDE 16
Collecting energy from marbles
What determines how much energy I get?
SLIDE 17
V = Joules Coloumb I = Coloumbs second V⋅I = Joules second
How much power does a light bulb use, if it is connected to 120V and draws 0.5 A?
Joules Coloumb Coloumbs second =
Joules/sec is called a Watt, abbreviated W.
SLIDE 18
A more exciting example
SLIDE 19
Why does the light bulb light up?
The filament gets hot and glows because:
A) the current is used up in the light bulb, becoming heat. B) the voltage accelerates electrons and they collide with the metal, losing their energy as heat. C) charges pile up inside the filament, and the repulsion of their electric fields creates heat. D) this is a trick question; the light bulb doesn't light up.
SLIDE 20
Bonus material: Alternating current
SLIDE 21