Silent Seven What 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 material o Measured by the amount of charge that passes a given point in a second o 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 current o 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 material o Greater resistance = less current for a given voltage o Unit: ohm (Ω) 4 factors determine resistance: o Material o 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 race o Powering the Promethean board’s remote control o Riding a roller coaster o Using a toaster o 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 travel o 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 t o Remember energy is measured in Joules o 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 A when it is connected to a 10.0 V-source Break down the question: o What is a resistor o What is a source o 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.