Electric Charges

SNC1PElectrical Applications2011

Electric Charges

• An atom is made of up protons, electrons, and neutrons.

Law of Electric Charges

• Two objects with like charges with repel each other

• Objects with opposite charge

Static Electricity and Discharge

• The shocks you get from walking across a carpet and touching a metal doorknob look like small lightning bolts – in fact, that is exactly what they are.

• Scientists used the word to describe materials that attract other materials after rubbing.

• Since the of the charged object, scientists called it .

• The study of static electricity is called

• Materials that do not carry a charge are said to be

• A list of materials that places materials in order of their tendency to lose electrons is called

• Material / • Tendency to lose e-
• Ebonite / • Least likely to give up electrons
• Rubber / •
• Polyethylene / •
• Dacron / •
• Cotton / •
• Silk / •
• Nylon / •
• Wool / •
• Glass / •
• Cat fur / • Most likely to give up electrons

• This list allows you to predict what will happen when two objects on the list are rubbed together.

• When two objects are rubbed together, the electrons move from one object to the other resulting in charged objects.

• The object that is

Testing for Charge

• A metal leaf can detect the presence of charge.

• A typical electroscope consists of a metal rob with a , and a at the bottom.

The Uses of Static Electricity

• The common uses of static electricity are in

• Most of the modern photocopy machines use static electric charges to make photo copies of documents.

• Recently invented laser and LED printers also use static electricity.

Methods of Charging

1. Friction

• When two substances are , one of them will lose electrons to the other. The object that has lost electrons will become positively charged. The object that has gained electrons will become negatively charged.

2. Conduction

• . Electrons flow from one object to another.

3. Induction

• A neutral object need only come close to a charged object to become negatively charged. . This is a rearrangement of charges.

Electric Discharge/Lightning

• Sometimes electric discharge is slow and quiet, while other times it is loud and quick. One of the most dramatic examples of static discharge is lightning!

• During a storm, particles move around in the clouds.

• As the electrons jump through the air, they produce intense light and heat. The light you see as a lightning bolt. The thunder you hear is the expansion of air due to the build up of heat.

• are used on tall buildings to provide a path for the electricity to follow to the ground.

• Grounding a conductor means to

Grounding

• Grounding electrical appliances around the home prevents serious and possibly fatal shocks.

• This is a simple technique that prevents fires and saves lives.

• Electronic instruments must be grounded because they are sensitive to electrical surges.

• Electrical wiring in houses, businesses, and industries are always grounded.

Insulators

• Insulators are materials that on or through the object.

SNC1PElectrical Applications2011

• Amber

• Cotton

• Ebonite

• Fur

• Glass

• Paper

• Plastic

• Porcelain

• Rubber

• Silk

• Sulfur

• Wood

• Wool

SNC1PElectrical Applications2011

Conductors

• Materials that on or through the objects are called conductors.

• Aluminum

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• Copper

• Gold

• Iron

• Magnesium

• Mercury

• Nickel

• Platinum

• Silver

• Tungsten

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Moving Charges

• Current electricity refers to through a conductor in a controlled way.

• The flow of electrons is also known as the flow of charge.

Electric Circuit

• The continuous path for an electron to flow (closed path) is called an

• A simple electric circuit includes an

• The energy source can be as small and portable as a battery or as large as a generating station.

• The load is a device that

• Conducting wires (connecting wires) join all the parts of the electric circuit together. They provide the pathway for electrons to flow.

• A switch controls current flow in an electric circuit.

• When the switch is and the electricity can flow.

• When the switch is

• You can describe a circuit with words or with actual pictures, but it is more practical to .

• These diagrams use symbols to represent each of the components in a circuit.

· A Direct Current (or DC) power supply For an electron to deliver its energy to the device being operated it must travel the full length of the circuit.

· ALTERNATING CURRENT (AC) means that

Measurements in Electric Circuits

Current

· Electric current is the flow of electrons through a circuit.

· Current is measured by an

Voltage

· Within a circuit, electrons flow through the wire from the negative terminal of the battery to the positive terminal with a certain amount of energy. This energy is called

· The potential difference is an electric circuit is the

· Voltage is measured using a

Resistance

· Electrical resistance is the . The symbol for resistance is R.

· The unit for resistance is an

Factors that affect electrical resistance:

i. Some materials have less resistance than others. Copper and gold will let electrons flow easily, while carbon slows down electrons.

i. The longer the wire, the more resistance

i. The skinnier the wire, the more resistance

i. The warmer the wire, the faster the electrons move and vibrate, but the more likely they will run into the walls of the wire so more resistance!

Safety Issues

· Electric Shocks

o You can be severely injured or even killed by electric shocks. Your muscles would contract violently and your body tissues could burn.

o Electric shocks can be caused by poorly insulated wires or if you touch you interrupt the flow of electrons with a wet hand.

o One of the most common dangers with circuits in homes involves overloading a circuit with too many plugs.

o The shape and size of prongs are designed to safely handle currents and voltages needed to operate a device. Most prongs only fit one way into an outlet. Also, outlet covers are used as a safety feature to prevent kids and pets from accidentally coming in contact with electricity.

o A fuse has a small metallic conductor with a melting point that is much lower that the melting point of the conducting wired. When current reaches a predetermined level (well below the amount of current needed to start a fire) the metal in the fuse melts and the current stops flowing!

o has the same function as a fuse but it accomplishes the task in a different way. Current flows through an armature, a contact, and a bimetallic strip. If the current increases, the temperature of the bimetallic strip increases and one of the metals expands. It will bend and release a hook that will open the switch and stop the flow through the circuit. To start the flow again, reduce the load and then simply push the armature back in place!

o Outlets near sources of water contain a special safety device called a ground fault circuit interrupter. Current changes when it comes in contact with water and these safety features detect the changes and immediately disconnect.

What is Energy?

· Energy is the ability to do a task. It comes in many forms:

· Such as gasoline or fireworks

· Warmth from a fire

· Voices or music

· Sunlight or microwaves

· Wind or running water

· Lightning, electricity used in our homes

· Electrical energy is the energy of moving charged particles.

· Energy can be transformed or changed from one form to another.

Example / Energy Transformation
Solar panel / Light energy to electrical energy
Fire / Chemical energy to thermal and light energy
Wind turbine / Mechanical energy to electrical energy
Car engine / Chemical energy to thermal and mechanical energy
Light bulb / Electrical energy to thermal and light energy

Generating Electricity

· Some electricity we use comes from batteries, but most comes from the

· And most of the energy distributed by the grid is produced in an electrical generating station.

o A generator is a machine that

o The energy in wind, flowing water or stream can be converted into electrical energy.

o The turbine spins and as they spin at high speeds near a powerful magnet.

Measuring Electrical Energy

· All energy is measured in

· How quickly we use energy per second is a

· The higher the wattage, the more energy it uses per second

· Sometimes a larger unit is used to measured energy –

o A kilowatt is 1000 x watt

o A kilowatt hour is 1000 W per hour

Non-renewable Sources

· A source of energy that is

· Thermal generation using Fossil fuels

o Thermal generation is one way of generating electricity.

o A common way to heat water is to burn fossil fuels. currently provides more than half of the world’s supply of electrical energy.

o Fossil fuels were formed from the remains of plants and animals that lived millions of years ago.

Advantages
Disadvantages

· Thermal Generation from Nuclear Energy

o Nuclear power plants are using materials such as Uranium as fuel. The nucleus of a Uranium atom stores a lot of energy.

Advantages
Disadvantages / ·

Renewable Energy Sources

· There are several sources of electrical energy that can be used over and over without running out.

Hydroelectric Generation

· In a hydroelectric generating station, the energy of falling water is used to move large blades of turbines connected to generators. Dams control the flow of water.

Advantages
Disadvantages

Wind Generation

· A modern wind turbine is made up of large blades mounted on a tall tower. The blades are connected to a generator. As the wind blows, the blades turn.

Advantages
Disadvantages

Photovoltaic Generation

· Electrical energy can be generated without using a turbine and generator. The most abundant source of energy on earth is the sun and it is free. A photovoltaic cell can capture the sun’s light and changes it directly to electrical energy.

Advantages
Disadvantages

Thermal Generation using Biomass

· Biomass is any form of bacteria, plant, or animal matter and it can be burned to produce thermal energy. The water is heated and the steam pushes the large turbines that are attached to the generator.

Advantages
Disadvantages

Geothermal Generation

· Geothermal energy plants are usually located in areas with volcanic activity. Geothermal generation uses wells drilled deep underground to access thermal energy. The hot geothermal gases are piped to a generating station where the heat turns water into steam, which then turns the turbines.

Advantages
Disadvantages

Electrical Use

· Electrical energy consumption is

· Some devices have a stand-by mode, which means that they continue to use energy as long as they are plugged into a wall outlet. This energy use is called a phantom load. Unplug electrical devices when not being used.

o Chargers from cell phones and MP3 players continue to use energy even after the device is fully charged.

· People use energy outside of their home as well, at schools, at work places, even driving down the street (street lights, traffic lights). Grocery stores need electricity to keep food cold. Businesses have computers and copiers and other devices that are always plugged in. Cities and towns use energy supply water to homes and run the waste water treatment plant.

· An energy meter keeps track of how many kilowatt hours are used. The meter is read each month and a bill is sent to the consumer.

Efficiency

· Not all electrical devices are energy efficient.

o A bulb converts electrical energy to light energy, but also has some energy wasted as thermal energy.

· Incandescent bulbs use four times as much energy as a compact fluorescent so a CFL is more efficient. LED lights produce very little thermal waste and use less energy. Led lights are the most efficient light.

o A kettle converts electrical energy to thermal energy but has quite a bit of steam lost.

Calculating Cost of Electricity

· To calculate the cost of using an electrical device, you need to know how much energy the device uses, as well as the price of each unit of energy.

o Energy used

§ Energy used (kw h) = wattage x time (h)

o Cost

§ Cost to operate ($) = energy used (kw h) x price ($)

Energy Conservation

· When we use less electrical energy in our daily lives, we reduce our personal energy consumption. Conserving energy now will reduce environmental damage and help ensure supply of energy in the long term.

§ and turn the power bars off when not in use.

§ Put devices into

§ when not in the room

§ Use appliances only when necessary and use them appropriately

§ for a more acceptable temperature (not as cold with AC in the summer, not as hot in winter)

§ , do only . Use cold water

§ to more efficient ones.