Electricity & Magnetism

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Electricity & Magnetism
Static, Currents, Circuits Magnetic Fields & Electro Magnets Motors & Generators

Mav Mark 11/28/11 What are the three components of an atom with their respective charges?

Mav Mark 11/29/11 Explain what happens when you get shocked while touching a metal door knob.

Mav Mark 11/30/11 Compare and contrast AC and DC currents.
Compare and contrast circuits in a series and in parallel.

It’s Electrifying Each sentence below is about electricity
It’s Electrifying Each sentence below is about electricity. Complete each sentence by using the letters that spell the missing word. (You will not use all of the letters for each word) The unit that measures electric power is the (k o w a v o t t g e). 2. A conductor has low (o c r e s e l I s I n t a n o r c e), so electric flows easily through it. When a light switch is off, the circuit broken, or (c s p o p w e h n). A device that raises or lowers voltage is a (t h r o a l n s f w o r z a m e r).

The answers are ... The unit that measures electric power is the WATT 2. A conductor has low RESISITANCE so electric flows easily through it. When a light switch is off, the circuit broken, or OPEN A device that raises or lowers voltage is a TRANSFORMER

Mav Mark 12/5/11 Compare and contrast acids and bases.
List 2 examples of each. Describe how you would determine if a substance is acidic or basic.

Mav Mark 12/6/11 Outline the pathway that electricity takes from a power plant to your home.

Mav Mark 12/7/11 Identify 6 forms of energy that may be used to cause a generator to turn and generate electricity.

Atoms… Have neutrons, protons, and electrons.
Protons are positively charged Electrons are negatively charged

Electrons… Are located on the outer edges of atoms…they can be moved.
A concentration of electrons in an atom creates a net negative charge. (More E than P makes Neg.) If electrons are stripped away, the atom becomes positively charged. (More P than E makes Pos.)

What is electricity? The collection or flow of electrons in the form of an electric charge 12

What is static electricity?
When two objects rub against each other electrons transfer and build up on an object causing it to have a different charge from its surroundings. Like the shoes rubbing against the carpet. Electrons are transferred from the carpet to the shoes. 13

Static Electricity The build up of an electric charge on the surface of an object. The charge builds up but does not flow. Static electricity is potential energy. It does not move. It is stored.

As electrons collect on an object, it becomes negatively charged
As electrons collect on an object, it becomes negatively charged. As electrons leave an object it attains a positive charges. Charges interact with each other: Often when you remove clothes from the clothes dryer, they seem to stick together. This is because some of the clothes have gained electrons by rubbing against other clothes. The clothes losing electrons become positive. The negative clothes are attracted to the positive clothes. Have you ever rubbed a balloon on your hair and stuck it on a wall? How do you think this works? 15

What causes you to be shocked when you rub your feet across carpet?
An electrical discharge is the passing of an electric current through the air from a negatively charged object to a positively charge object. This is what causes lightning! 16

Static vs. Current Electricity
Static electricity is stationary, whereas current electricity is flowing very rapidly through a conductor. The flow of electricity in current electricity has electrical pressure or voltage. Electric charges flow from an area of high voltage to an area of low voltage. Water pressure and voltage behave in similar ways. 17

Electricity that moves…
Current: The flow of electrons from one place to another. Measured in amperes (amps) Kinetic energy

How can we control currents?
With circuits. Circuit: is a path for the flow of electrons. We use wires.

There are 2 types of currents:
Direct Current (DC) – Where electrons flow in the same direction in a wire.

There are 2 types of currents:
Alternating Current (AC) – electrons flow in different directions in a wire

Direct current versus alternating current
AC vs DC : What’s the difference? Go to this website and click the button for DC then for AC to visually see the difference between the two. You can see that the DC source is a battery – current flows in one direction. The AC source is the generator and the current alternates once for each revolution. 22

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There are 2 types of circuits:
Series Circuit: the components are lined up along one path. If the circuit is broken, all components turn off.

Series Circuit

There are 2 types of circuits:
Parallel Circuit – there are several branching paths to the components. If the circuit is broken at any one branch, only the components on that branch will turn off.

Parallel Circuit

Open circuit Vs. Closed circuit
A closed circuit is one in which the pathway of the electrical current is complete and unbroken. An open circuit is one in which the pathway of the electrical current is broken. A switch is a device in the circuit in which the circuit can be closed (turned on) or open (turned off). 28

Household Wiring Most household wiring is designed with a combination of parallel circuits. Electrical energy enters the home usually at a breaker box or fuse box and distributes the electricity through multiple circuits. A breaker box or fuse box is a safety feature which will open a circuit. 29

Conductors vs. Insulators
Conductors – material through which electric current flows easily. Insulators – materials through which electric current cannot move.

Examples Conductors: Insulators: Metal Water (not pure) Styrofoam
Rubber Plastic Paper

What is Resistance? The opposition to the flow of an electric current, producing heat. The greater the resistance, the less current gets through. Good conductors have low resistance. Measured in ohms.

What Influences Resistance?
Material of wire – aluminum and copper have low resistance Thickness – the thicker the wire the lower the resistance Length – shorter wire has lower resistance Temperature – lower temperature has lower resistance

The unit for measuring resistance is the ohm (Ω).
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What is Voltage? The measure of energy given to the charge flowing in a circuit. The greater the voltage, the greater the force or “pressure” that drives the charge through the circuit.

Difference b/t Volts and Amps
Example – you could say that… Amps measure how much water comes out of a hose. Volts measure how hard the water comes out of a hose.

Resistance = Voltage / Current
Ohm’s Law Resistance = Voltage / Current Ohms = Volts / Amps

Practice with Ohm’s Law
Volts Amps 4 100 25 15 150 10 2 30 9 45 5 6 48 8

Electrical Power Electrical Power is the product of the current (I) and the voltage (v) The unit for electrical power the watt (W) Example Problem: How much power is used in a circuit which is 110 volts and has a current of 1.36 amps? P = I V Power = (1.36 amps) (110 V) = 150 W 39

What is magnetism? Magnetism is the properties and interactions of magnets. Magnets produce magnetic forces and have magnetic field lines 40

Magnets have two ends or poles, called north and south poles.
Unlike poles of magnets attract each other and like poles of magnets repel. 41

The earth is like a giant magnet!
The nickel iron core of the earth gives the earth a magnetic field much like a bar magnet. 42

Electricity and Magnetism – how are they related?
When an electric current passes through a wire a magnetic field is formed. 43

What is an electromagnet?
When an electric current is passed through a coil of wire wrapped around a metal core, a very strong magnetic field is produced. This is called an electromagnet. 44

What are electric motors?
An electric motor is a device which changes electrical energy into mechanical energy. 45

How does an electric motor work?
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Carefully study the next diagrams:
We have seen how electricity can produce a magnetic field, but a magnetic field can also produce electricity! How? Moving a loop of wire through a magnetic field produces an electric current. This is electromagnetic induction. A generator is used to convert mechanical energy into electrical energy by electromagnetic induction. Carefully study the next diagrams: 48

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Two kinds of batteries: dry cell and wet cell batteries.
What are batteries? Batteries are composed of a chemical substance which can generate voltage which can be used in a circuit. Two kinds of batteries: dry cell and wet cell batteries. The zinc container of the dry cell contains a moist chemical paste surrounding a carbon rod suspended in the middle. (Alkaline and Lithium) 50

Wet cell batteries are most commonly associated with automobile batteries.
A wet cell contains two connected plates made of different metals or metal compounds in a conducting solution. Most car batteries have a series of six cells, each containing lead and lead oxide in a sulfuric acid solution. 51

pH Scale Measures how acidic or basic a substance is by its hydrogen ion concentration Ranges from 0 to 14 A pH of 7 is neutral A pH less than 7 is acidic. A pH greater than 7 is basic.

Acids vs. Bases Acids Bases
High hydrogen [H+] and hydronium ion [H3O+]concentration Taste sour Ex. Lemon juice, coke Bases High hydroxide ion concentration [OH-] Taste bitter Feel slippery Ex. Soap, bleach

Strong Acids and Bases Ionize completely in water
Good conductors of electricity Weak Bond Strength

Indicators Litmus paper Phenolphthalein Acids turn paper red
Bases turn paper blue Phenolphthalein Acids are clear Bases are pink

Neutralization Acid + Base → Salt Water HCL + NaOH → NaCl + H2O

Common Acids Sulfuric acid: used in car batteries and used to make paper, detergents, fertilizer, and paint Nitric acid: used to make fertilizers, rubbers, and plastics Carbonic and phosphoric acid: Used in soft drinks Citric acid and ascorbic acid: found in orange juice Hydrochloric acid: stomach acid and metal production

Common Bases Sodium Hydroxide: used to make soap and paper
Calcium hydroxide: used to make cement, mortar, and plaster Ammonia: used in many household cleaners and to make fertilizer Magnesium hydroxide & Aluminum hydroxide is used in antacids to treat heart burn

How is electricity generated?
Most is produced at power plants. Turbines with magnets inside are turned by various energy sources. The turbines are surrounded by copper wire. The magnetic field generate by the turbine causes electrons in the copper wire to move from atom to atom causing electricity.

How it gets from plant to places
Electricity leaves the power plant and is sent over high-power transmission lines on tall towers. Electricity loses some of its strength as it travels. Transformers boost or “step up” its power to help it along the way. Transformers is a device that can increase or decrease electric voltage.

How it gets from plant to places
When electricity gets closer to its destination, voltage must be decreased. Different transformers then “step down” the electricity’s power. Thinner wires on smaller towers carry the electricity to homes.

Transformers V2/V1 = N2/N1 As the number of coils increases, the amount of volts increases. As the number of coils decreases, the amount of volts decreases.

Power Grid Power plant → substation → “step up” transformer → transmission lines → substation → step down transformer → junction Box → outlet → appliance circuit

Transformers

Fossil Fuels What is NZ generation like – mostly hydro, no nuclear
H/O NZ and its power generation H/O task 6 Kids research pros and cons of one method of generation, create powerpoint/ poster, present to class 5 mins All vote on best for NZ and why 65

Hydro Dam Water rushes through to the Clutha River from Clyde Dam in Central Otago on the South Island of New Zealand. The largest hydroelectric dam in New Zealand is the Clyde Dam which was built along the Clutha River near the town of Clyde and generates a capacity of 400 megawatts. There are a million cubic meters of concrete in the dam with a further 200,000 in the powerhouse. The Clyde Dam stands at 100 meters in height, 70 meters wide at the base The Waikato River system is the most highly developed for electricity generation in New Zealand.  It supplies eight hydro-electric stations and provides cooling water for two geothermal and one thermal station.                       The eleven stations on the Waikato produce 65% of the North Island's power generation and approximately 25% of New Zealand's hydro power.  This is 15% of New Zealand's total power. 66

Hydroelectric power

Nuclear power

Wind Power

Tidal Power

Geothermal The first geothermal power station was built at Landrello, in Italy, and the second was at Wairekei in New Zealand. The centre of the Earth is around 6000 degrees Celsius - hot enough to melt rock. Even a few kilometres down, the temperature can be over 250 degrees Celsius. In general, the temperature rises one degree Celsius for every 36 metres you go down. In volcanic areas, molten rock can be very close to the surface. Hot rocks underground heat water to produce steam. We drill holes down to the hot region, steam comes up, is purified and used to drive turbines, which drive electric generators. 71

Solar Solar water heating Photovoltaic cells Solar furnace
Water piped through thin pipe gets heated and stored in insulated tank Photo cells turn solar energy into electrical not very efficient at the moment Furnace is an array of mirrors which concentrates suns rays to heat water into steam and turn turbine - possibly arranged as a tower full of turbines surrounded by greenhouse Demo solar cell lighting bulb/ whistle 72