Electricity Lecture 2 Last time We talked about

Electricity Lecture 2

Last time … We talked about electricity. Charges, concepts. It is amazing how many things we can make electricity do for us. It makes things hot, it makes things cold. It lights up. It makes things move and stop, allows us to transmit and receive information, and it does arithmetic for us.

Electricity Problem: some numbers are involved. We need to know, sometimes, how much current is needed, how much voltage is needed to do a job. And we need to know how to make that happen. If you ever want to know WHY we are doing something or talking about something please ask.

Electricity In electricity, we know something is flowing. Engineers say it is positive charges, everyone else says negative charges. It does not matter.

Electricity

Measuring Electricity? There are many ways to measure electricity. Don’t let the numbers get in the way. They are constraints, like colours and speeds and pressures. There is nearly always a range of what is acceptable.

Measuring Electricity The multimeter (DMM) or digital volt meter (DVM) is critical. We can’t see what’s happening, unlike a drawing or painting. We infer what’s going on by measuring things.

Measuring Electricity This is a cheap one. We will be manually selecting both the type of meter and the range within which you will be measuring.

Measuring Electricity Start by selecting the range you think is closest to the value you will be measuring. Always start at the highest value: 100 volts, then 200, then 20 etc.

Measuring Electricity In this example, we’re measuring something I think is around 6 volts, so I start in the range of 0 – 20 volts. I'm measuring dc current, so I select the range in the area next to the “V” with a dashed line. (The “V” with the wavy line is volts of ac)

If I move dial to the 0 – 200 volt range, the meter displays the same value, but it moves over one decimal place to make. And notice we’re losing some resolution (the hundredths place) in the process. Selecting the range closest to the value you are measuring will give you the most precise measurement (most decimal places. ) Meters

We went from 0 -20 to 0 -200. We might need an extra digit. Let’s step up one again. Meters

We went from 0 -200 to 0 -1000. The meter is displaying the same value, but it moves over one decimal place to make room for a sign (+ or -) and larger, four digit number. And notice I'm losing some resolution (the tenths place) in the process. Meters

Going down: The range below 0 – 20 volts has a small letter “m” indicating that it is a range measuring millivolts (thousandths of a volt. ) Note: 0 – 2000 thousandths of a volt is the same as measuring 0 – 2 volts. 1? ? Meters

The voltage we are measuring is 5. 71 volts, the meter displays a numeral 1 at the left of the display. 5. 71 V is bigger than 2 V This is what the display looks like when it is measuring a value that is “out of range. ” Each meter indicates this in a different way: “E”, “Error”, flashing, or smoke. Meters

AC? DC?

What uses AC, what DC? Most things actually use DC. It gets converted into DC inside the device (TV, Radio, computer, etc) AC is better for transmitting over distances) AC • • • Vacuum cleaner Stove Fridge Lights Pumps DC • • computer Television Radio CD/DVD/AM

What Is Electricity? US & Canada domestic supply – 120 V AC • Household circuit breakers typically provide a maximum of 15 A or 20 A of current to a given set of outlets. • 22 -inch/56 -centimeter Portable Television 290 m. A • Tungsten light bulb (60– 100 W): 500– 830 m. A • Toaster, kettle 16. 6 A • Immersion heater 38. 3 A

What Is Electricity? Current represents the amount of flow. Using a water/pipe analogy, the volume of water through a pipe is related to the pressure applied. Electrical pressure is related to the charge difference between two places.

What Is Electricity? Electrical pressure is measured in Volts, named after another guy: Count Alessandro Giuseppe Antonio Anastasio Volta (18 February 1745 – 5 March 1827) was an Italian[1][2] physicist known especially for the invention of the battery in 1800.

What Is Electricity? The volt is defined as the value of the potential difference (voltage) across a conductor when a current of one ampere dissipates one watt of power in the conductor. It is also equal to the potential difference between two points 1 meter apart in an electric field of 1 newton per meter. It is the potential difference between two points that will impart one joule of energy per coulomb of charge that passes through it.

What Is Electricity? None of these are satisfying. • • Nerve cell resting potential: around 75/1000 V Single-cell, rechargeable Ni. MH or Ni. Cd battery: 1. 2 V Mercury battery: 1. 355 V Single-cell, non-rechargeable alkaline battery (e. g. , AAA, C and D cells): 1. 5 V • Li. Fe. PO 4 rechargeable battery: 3. 3 V • Lithium polymer rechargeable battery: 3. 75 V (see Rechargeable battery#Table of rechargeable battery technologies) • Transistor-transistor logic/CMOS (TTL) power supply: 5 V

What Is Electricity? • PP 3 battery: 9 V • Automobile electrical system: nominal 12 V, about 11. 8 V discharged, 12. 8 V charged, and 13. 8– 14. 4 V while charging (vehicle running). • Household mains electricity: , 120 V in North America, • Rapid transit third rail: 600– 750 V (see List of current systems for electric rail traction) • High-speed train overhead power lines: 25 k. V RMS at 50 Hz, but see the list of current systems for electric rail traction and 25 k. V at 60 Hz for exceptions. • High-voltage electric power transmission lines: 110000 volts and up (1. 15 MV RMS was the record as of 2005[citation needed]) • Lightning: Varies greatly, often around 10000 v.

How do we make electricity? Many ways: 1. Chemicals A cell or battery is a chemical package that makes electricity. Simple example: a lemon with metal bits stuck into it can make electricity.

How do we make electricity? Many ways: 2. Mechanical devices A magnet moving near a wire will create electricity in the wire. Ditto moving wires near a magnet. (Generator) Hydro plants, nuclear plants, coal plants and wind generators all use this.

How do we make electricity? 3. Direct light conversion Light knocks electrons off of atoms and they are guided through wires to where they can be used. Solar cells

How Can Electricity Do Stuff? That’s a really complex question. Most simply, electricity can do work by making heat. Heat is a by-product of all work, all motion, all physical processes. Electricity passing through a wire makes heat, some wires more than others. Some wires create so much heat they glow (light bulb). Some hot wires make toast and melt cheese.

How Can Electricity Do Stuff? Electricity moves charge from place to place. Since + and – charges attract each other, electricity can be used to cause motion by moving charges to places where their attraction will cause motion. Electric motors, rail guns.

How Can Electricity Do Stuff? Electric current flow creates something called an electric field, which is really just a mapping in 3 D space of how near one is to how much flow. A wire in a moving electric or magnetic field can capture some of the flow and that can be amplified. Radio, audio.

How Can Electricity Do Stuff? Electric current flow creates something called an electric field, which is really just a mapping in 3 D space of how near one is to how much flow. A wire in a moving electric or magnetic field can capture some of the flow and that can be amplified. Radio, audio.

Next … Next we will look at the concept of a circuit and at basic electric/electronic components.