Silent Seven What type of static charging occurs when… 1.You rub a balloon against your hair?...

Silent SevenWhat type of static charging occurs when…1. You rub a balloon against your

hair?

2. When a negatively charged ruler touches a metal rod, electrons move from the ruler to the rod.

3. A charged balloon causes the charges in a metal can to rearrange?

4. Give an example of static discharge.

Recap:

Conduction, Induction, or Friction?

Static discharge

• Lightning releases a large amount of electrical energy…

• BUT lightning can’t be used to power your TV, cell phone, video game, or lights because it only lasts for an instant.

• Many things require electric charges that flow continuously, and with static electricity, charges build up, but do not flow.

• Electric current is the continuous flow of electrons through a materialo Measured by the amount of charge that

passes a given point in a secondo Unit: amperes

Lower current

Higher current

• Electric current requires an electric circuit – a complete, unbroken path through which charges can flow.

• A conductor is a material in which charges can flow easily.• Examples: metals (copper, gold, aluminum)

• An insulator is a material in which charges cannot flow easily.• Examples: rubber, wood

• Think about a roller coaster- when you are at the top of that first big hill, what causes you to move down?

• POTENTIAL ENERGY STORED BY GRAVITY!

• Just like the roller coaster needs to gain potential energy using a motor to move…

• Electric charges need a potential energy difference to move.

• Voltage is the difference in electrical PE between 2 places in a circuit. o Unit: Volt (V)o Causes a currento The amount of force pushing an electric current

• A battery is a voltage source that changes chemical to electrical energy

• Resistance is the measure of how difficult it is for charges to flow through a materialo Greater resistance = less current for a given

voltageo Unit: ohm (Ω)

• 4 factors determine resistance:o Materialo Length (long wire = more resistance)o Diameter (smaller diameter = more

resistance)o Temperature (higher temp. = more

resistance)

• Ohm’s Law relates current (I), resistance (R), and voltage (V)

• Voltage = current x resistance

• If voltages increases, current

• If voltages decreases, current

• If resistance increases, current

• If resistance decreases, current

• Phet circuits simulation- exploring voltage, current, and resistance

Silent Seven• Describe the following energy transformations:

o Running a raceo Powering the Promethean board’s remote

controlo Riding a roller coastero Using a toastero Powering a car engine

Bill Nye• Answer the questions on your sheet• Heads up• Remain silent in your seat

Add to Resistance• Path of least resistance: easiest way for electrons

to travelo Why birds do not get shocked.

Calculating Electricity• Ohm’s: Voltage = Current * Resistance• Electric Power: rate at which one form of energy

is converted to another.• P = I x V

o Remember power is measured in watts or kilowatts

• Electric Energy: The total amount of energy used by an appliance E = P x to Remember energy is measured in Jouleso Measured in kilowatt-hours (kWh)o This is what the electric company uses to show on your

meters to charge you for electricity.

Electricity Practice• Ohm’s

• The current through a resistor is 0.025 A when it is connected to a 10.0 V-source

• Break down the question:o What is a resistoro What is a sourceo What equation do I need to use?

• A hair dryer has a power rating of 1,200 W and uses a standard voltage of 120 V. What is the current through the hair dryer?

• Break down the question:o What do I know?o What am I looking for?o What equation am I going to use?

• A refrigerator uses a standard voltage of 120 V and has a current of about 4.2 A. What is its power rating?

• Break down the question:o What do I know?o What am I looking for?o What equation do I use?

1. The same refrigerator uses a standard voltage of 120 V and has a current of about 4.2 A. You use this fridge for 24 hours. How much electrical energy is used?

Break down the question:1. What do I know?2. What am I looking for?3. What equation do I use?

2 . Every time you open the fridge you use 140 V. Some one in your family open the fridge and stare at what is inside for 2 minutes about 15 times a day. How much electrical energy do you use in addition to the energy you already use to power the refrigerator?

o *** Convert minutes into hours***

Homework• Finish sheets• Go home and look at the different appliances in

your home. Look at their power ratings. Write them down and be prepared to share them during tomorrow’s silent seven.