WEEK 10

ELECTRICITY 3

3. How does it work?

Safely construct series and parallel circuits that include lights, switches, ammeters, voltmeters, variable resistors and multimeters.
Compare series and parallel circuits with respect to the behaviour of voltage and current.
Compare the use of series and parallel circuits in homes.
Outline how the development of electrical circuits in smartphone technology involved specialist teams from different branches of Science.

MONDAY P5 L3

Circuit Symbols

9E Circuit Symbols.pdf

Practical 3.1 Circuits

9E 13 Series Parallel Prac.pdf

9E Circuit practice.pdf

TUESDAY P3,4 MO4

Continue Circuit Practical

TASK 3.1

Complete the Circuit Puzzles at right

Hint:

Increasing the number of bulbs in a series circuit increases the resistance (more bumps in the road) and so decreases the current (the delivery vans slow down) and therefore decreases the brightness of the bulbs (the vans lose more jewels). In a series circuit, the voltage is equally distributed among all of the bulbs (only one road, all the vans have to move at the same speed).

Bulbs in parallel are brighter than bulbs in series (more pathways, less bumps, vans can move faster). In a parallel circuit the voltage for each bulb is the same as the voltage in the circuit.

9E Circuit Puzzles.docx

Task 3.2 About circuits, symbols

View and engage with

http://www.learningcircuits.co.uk/flashmain.htm (basic)
http://www.switchedonkids.org.uk/electrical-safety-in-your-home (safety, basic)

Go to Quiz for circuit components https://www.andythelwell.com/blobz/guide.html

TASK 3.3

Complete worksheet from simulation

https://phet.colorado.edu/en/simulation/circuit-construction-kit-dc

--> click: play intro

Circuit Construction Kit: DCExperiment with an electronics kit! Build circuits with batteries, resistors, light bulbs, fuses, and switches. Determine if everyday objects are conductors or insulators, and take measurements with an ammeter and voltmeter. View the circuit as a schematic diagram, or switch to a lifelike view.

5. Circuit Construction.docx

TASK 3.4 QUICK DRAW

Draw a parallel circuit with two light bulbs and a switch (which turns only one light bulb off)

2. Draw a series circuit with an ammeter and a closed switch

3. Draw a parallel circuit with an ammeter measuring the current flowing through the first bulb and a voltmeter measuring the voltage going
across the second light bulb

4. Draw parallel circuit where the first branch has one bulb, the second branch has two bulbs and the third branch has one bulb with a voltmeter
measuring the voltage of that light bulb

For "switch is closed", in the diagram at right, it means "switch is turned off."

THURSDAY P2 L3

TASK 3.5 Circuits in Our Lives

Read and copy a summary into your book https://www.hunker.com/12322458/what-appliances-have-series-circuits for series circuits in the home.
Research and make notes on parallel circuits in the home.
Research to outline how the development of electrical circuits in smartphone technology involved specialist teams from different branches of Science.

TYPES OF CURRENT

View video

AC vs DC https://www.youtube.com/watch?v=BcIDRet787k [6.23]

How Electrons Flow

Electricity is the flow of electrons through a wire, but there are actually two different ways the electrons move within the wire. electricity has specific movements it makes in the wires. These currents are called alternating current (AC) and direct current (DC).

Direct Current

With DC electricity, connecting a wire from the negative (−) terminal of a battery to the positive (+) terminal will cause the negative charged electrons to flow swiftly through the wire toward the positive terminal. The same thing happens with a DC generator, where the motion of coiled wire through a magnetic field pushes electrons out of one terminal and attracts electrons to the other terminal. With DC, electrons move in one direction, from (-) negative to (+) positive. It's a constant current, flowing continuously until either it's switched off or its power source runs out.

In a circuit with a light bulb, the on/off switch acts as a gate for the electron flow. When it's on the circuit is complete, allowing the electrons to flow. After passing through the switch, electrons flow to the light bulb. The filament (coiled wire) in the bulb lights up, taking the energy from the electrons, which are then drawn to the positive terminal on the battery to be re-energised. This process continues until the battery eventually loses its energy.

Direct Current can be generated in several ways:

Batteries provide DC, which is generated from a chemical reaction inside of the battery
An AC generator equipped with a device called a "commutator" can produce direct current
A device called a "rectifier" converts AC to DC (We use this in the lab).

https://www.school-for-champions.com/science/ac.htm#.X2h1UmgzZPY

Alternating Current

Alternating Current is the type of electricity commonly used in homes and businesses throughout the world.

With AC current, electrons don't really flow, they simply vibrate back and forth from negative to positive and positive to negative. It isn't a continuous vibration either. The electrons vibrate in time or in sync with one another, and this timing is controlled by modifying the speed of the generator. We call this electrical timing hertz (Hz). The direction alternates between 50 and 60 times per second, depending on the electric system of the country.

In Australia, AC electricity is generated at 50 hertz. The electrons vibrate and bang into each other, transferring their energy from positive to negative and back again 50 times per second. This means that when a circuit running on AC has a light bulb, it doesn't have a steady flow of positively charged electrons running through it like it does on DC power, so the light is not constant either. It flickers on and off for every cycle of electron charge transfer, at 50 complete cycles per second. However, this is too fast for the human eye to see, so it appears to be a constant light.

https://www.school-for-champions.com/science/ac.htm#.X2h1UmgzZPY

Advantages and Disadvantages

High voltages are more efficient for sending electricity great distances, but then the high voltages from the power station need to be easily reduced to a safer voltage for use in the house. The major advantage that AC electricity has over DC electricity is that AC voltages can be readily transformed to higher or lower voltage levels. It is much more difficult to do that with DC voltages. Changing voltages is done by the use of a transformer.

The biggest advantage of DC electricity is that it is far easier to store than AC electricity, especially on a small scale. Storing electricity when it is made, for use later when it is needed, is critical for mobile/mains-free devices.

Devices

Many electric devices—like light bulbs—only require that the electrons move. It doesn't matter if the electrons flow through the wire or simply move back-and-forth. Thus a light bulb can be used with either AC or DC electricity.

AC electricity allows for the use of a capacitor and inductor within an electric or electronic circuit. These devices can affect the way the alternating current passes through a circuit. They are only effective with AC electricity. A combination of a capacitor, inductor and resistor is used as a tuner in radios and televisions. Without those devices, tuning to different stations would be very difficult.

https://www.school-for-champions.com/science/ac.htm#.X2h1UmgzZPY

EXTRA FOR INTEREST

View video

Edison vs Tesla https://www.youtube.com/watch?v=WcI1lS0teAo [15.12]

Battle of the Currents

Almost every home and business is wired for AC. However, this was not an overnight decision. In the late 1880s, a variety of inventions across the United States and Europe led to a full-scale battle between alternating current and direct current distribution.

In the late 1800s, Thomas Edison proposed a system of small, local power plants that would power individual neighborhoods or city sections, but power plants needed to be located within 1.5km of the end user. This limitation made power distribution in many areas extremely difficult, if not impossible.

In 1888, George Westinghouse, a famous industrialist from Pittsburgh, purchased Nikola Tesla's patents for AC motors and transmission. Westinghouse worked to perfect an AC distribution system. Transformers provided an inexpensive method to step up the voltage of AC to several thousand volts and back down to usable levels in houses, shops and factories . At higher voltages, the same power could be transmitted at much lower current, which meant less power lost due to resistance in the wires. Large power plants could be located many kilomatres away and service a greater number of people and buildings.

Over the next few years, Edison ran a campaign to highly discourage the use of AC in the United States, which included lobbying state legislatures and spreading disinformation about AC. Edison also directed several technicians to publicly electrocute animals with AC in an attempt to show that AC was more dangerous than DC. In attempt to display these dangers, Harold P. Brown and Arthur Kennelly, employees of Edison, designed the first electric chair for the state of New York using AC.

In 1891, the International Electro-Technical Exhibition was held in Frankfurt, Germany and displayed the first long distance transmission of AC, which powered lights and motors at the exhibition. Several representatives from what would become General Electric were present and were impressed by the display. The following year, General Electric formed and began to invest in AC technology.

Westinghouse won a contract in 1893 to build a hydroelectric dam to harness the power of Niagara falls and transmit AC to Buffalo, NY. The project was completed in 1896 and AC began to power industries in Buffalo. This marked the decline of DC in the United States. While Europe would adopt an AC standard of 220-240 volts at 50 Hz, the standard in North America would become 120 volts at 60 Hz.

Swiss engineer René Thury used a series of motor-generators to create a high-voltage DC system in the 1880s, which could be used to transmit DC power over long distances. However, due to the high cost and maintenance of the Thury systems, HVDC was never adopted for almost a century.

With the invention of semiconductor electronics in the 1970s, economically transforming between AC and DC became possible. Specialized equipment could be used to generate high voltage DC power (some reaching 800 kV). Parts of Europe have begun to employ HVDC lines to electrically connect various countries.

HVDC lines experience less loss than equivalent AC lines over extremely long distances. Additionally, HVDC allows different AC systems (e.g. 50 Hz and 60 Hz) to be connected. Despite its advantages, HVDC systems are more costly and less reliable than the common AC systems.

In the end, Edison, Tesla, and Westinghouse may have all been right. AC and DC can coexist and each serve a purpose.