Electricity 7-1

Atoms contain particles called protons, neutrons, and electrons. Protons and electrons have electric charge, and neutrons have no electric charge.

Electric Charge ___________________ have a ______________ electric charge ___________________ have a ______________ electric charge In most atoms, the charges of the protons and electrons _______________ each other out and the atom has __________________________________ Objects with no net charge are said to be __________________________. Sometimes electrons are not held tightly in atoms. Atoms become charged by _________________ or _________________ electrons. One item loses electrons and is no longer neutral. The other item gains an electron and has a ______________________________. – When an atom __________ an electron, it becomes ____________ charged.– When an atom __________ an electron, it becomes ____________ charged.

Static Electricity Static electricity is the accumulation of excess electric charges on an object

Law of Conservation of Charge Electrically charged objects obey the following rules: Law of conservation of charge – charge may be ____________________ from object to object, but it cannot be ________________ or ____________

• Whenever an object becomes charged, electric charges have moved from one place to another.

• Why do you get “shocked”?• Electrons transfer from one item to another – build-up of electron• If you reach for a metal doorknob after walking across a carpet, you

might see a spark. • The spark is caused by electrons moving from your hand to the

doorknob.

Charges can act on each other even at a ________________, because any charge that is placed in an electric field will be __________________ or ___________________ by the field

Charges Exert Forces • Opposite charges ________________ each other,• Like charges ______________ each other. • The force between electric charges also depends on the _____________

between charges. The force decreases as the charges get farther apart.

What is an Electric Field? Electric Field An electric field surrounds every electric charge and exerts the __________ that causes other electric charges to be attracted or repelled.

Any charge that is placed in an electric field will be ___________________ by the field.

Movement of Electrons Electrons move more easily through ______________________________.

What are examples of good conductors?________________________________________________________

Electrons do not move easily through _____________________________.

What are examples of good insulators?________________________________________________________

How is Electric Charge Transferred? Charging by _________________________ The process of transferring charge by ____________________ or _________________ Example: ____________________________________________________ Rubbing two materials together can result in a transfer of ______________. Then one material is left with a positive charge and the other with an equal amount of ___________________ charge.

Charging by Induction Because electrical forces act at a distance, charged objects brought near a neutral object will cause electrons to ________________ their positions on the neutral object. Example: a negatively charged balloon near your sleeve causes an area of your sleeve to become positively charged by ________________________.

The balloon on the left is neutral. The balloon on the right is negatively charged. It produces a positively charged area on the sleeve by repelling electrons. The ____________________of electrons on a ______________object caused by a nearby charged object is called __________________________.

Static Electricity Static _______________________– A _________________of ________________through the air between two objects because of a buildup of ____________ electricity– Example: lightning

Lightning Lightning is a large __________________________________. A static discharge is a transfer of charge between two objects because of a buildup of static electricity. A thundercloud is a mighty generator of static electricity. As air masses move and swirl in the cloud, areas of positive and negative charge build up. Eventually, enough charge builds up to cause a static discharge between the cloud and the ground.

As the electric charges move through the air, they collide with atoms and molecules. These collisions cause the atoms and molecules in air to emit light. Lightning also generates powerful _________________________. The electrical energy in a lightning bolt rips electrons off atoms in the atmosphere and produces great amounts of heat. The heat causes air in the bolt’s path to expand rapidly, producing sound waves that you hear as _____________________.

Electric Charge _________________________ – using a ___________________ to direct an electric charge into the ground.

The presence of electric charges can be detected by an ________________

Electroscope

When the device is not charged, the leaves hang straight down. Notice the position of the leaves on the electroscope when they are A uncharged, B negatively charged, and C positively charged.

Question 1The law of conservation of charge states that ______________________________________________________________________________________

Question 2Which of the following is the best conductor of electricity?__________________________________________

Question 3The accumulation of excess electric charge on an object is called ______________________________.

What do you think happens when you get static electricity in your hair?

7-2 Electric Currents.What is an Electric Current? The ___________________________ through a wire of conductor is called ___________________________ Current is usually the flow of _____________________ Electric current is measured in __________________ (___) Charges flow from ___________ voltage to __________ voltage

Sources of Electricity A _________________________ produces a voltage difference between its _____________ container and its _______________ suspension rod, causing current to flow between them Sources of Electricity

A ____________________________ contains two connected plates made of different ___________________ in a conducting _________________

Sources of Electricity ____________________ have a voltage difference across the __________ _____________ of an electrical outlet, and a generator at a ______________ _________________ provides this _________________________________

What is Resistance? ________________________________– _________________________ to the _____________ of electrons– electrical energy is converted to _______________________ &__________– all materials have ____________ electrical resistance– measured in ______________ (____) Resistance depends on…

– the _____________________________– ________________________________

_____________ resistance in ________________ wires– ________________________________

_____________ resistance in _________________ wires– ________________________________

_____________ resistance at ___________ temps

Ohm’s Law Ohm’s Law – the current in a circuit equals the voltage difference divided by the resistance

V: potential difference (V)I: current (A)R: resistance (W)

Voltage ________________ when ________________ increases. Voltage ________________ when ________________ increases.

Ohm’s Law Problem A lightbulb with a resistance of 160 W is plugged into a 120-V outlet.

What is the current flowing through the bulb?

What property of electric current causes light bulbs to give light?

Electrical Circuits Circuits rely on generators at power plants to produce a _____________ __________________ across the outlet, causing the charge to move when the ______________________

Circuit Components

A - battery C - light bulb

V = I × R

B - switch D - resistor

Example Hair dryer plugged into wall outlet Generator at power plant produces voltage difference Dryer and circuit in house contain conducting wires to carry current Hair dryer turns electrical energy into thermal energy and mechanical

energy Unplug hair dryer opens circuit and breaks path of current

Types of Circuits _________________ circuit – the current has only ___________________ to flow through _________________ circuit – contains _____________________________ for current to move through

Series Circuit current travels in a _________________ path

– _______________________ - one _________ ____________ the flow of current

current is the ______________ throughout circuit

– lights are ______________ brightness each device receives a ________________ of the total voltage

– gets ________________ as lights are added

Example: __________________________

Parallel Circuit current travels in __________________ paths

– one break ______________________________ flow current varies in ________________________

– takes path of ____________ resistance– “_____________” light would be dimmer

each device receives the ______________ voltage– ___________________ when lights are added

Example: ________________________________

Household Circuits Combination of _________________ circuits

– too many devices can cause wires to _________________ Safety Features:

– ____________ - metal _____________, breaking circuit– _____________________ - bimetallic strip __________ when hot, breaking circuit

Household Fuse Box Circuit Breaker Box

Electrical Power

Electrical Power - rate at which electrical energy is ___________________ to another form of energy P: _________________ (____)

I: _________________ (____)V: ________________________ (__)

Electrical PowerA calculator has a 0.01-A current flowing through it. It operates with a potential difference of 9 V. How much power does it use?

Electrical Energy Electrical Energy– energy use of an appliance depends on power required and time used

E: __________________ (__________)P: __________________ (________)t: __________________ (_____)

Electrical EnergyA refrigerator is a major user of electrical power. If it uses 700 W and runs 10 hours each day, how much energy (in kWh) is used in one day?

Why do homes have a fuse box or circuit breaker?

P = I × V

E = P × t

How does it work?