Atoms Contain Particles Called Protons, Neutrons, and Electrons

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

n ______have a ______electric charge

n In most atoms, the charges of the protons and electrons ______each other out and the atom has ______

n Objects with no net charge are said to be ______.

n Sometimes electrons are not held tightly in atoms.

n Atoms become charged by ______or ______electrons.

n 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.

Static Electricity

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

Law of Conservation of Charge

n Electrically charged objects obey the following rules:

n 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.

n 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?

n Electric Field

n An electric field surrounds every electric charge and exerts the ______that causes other electric charges to be attracted or repelled.

n Any charge that is placed in an electric field will be ______by the field.

Movement of Electrons

n Electrons move more easily through ______.

What are examples of good conductors?

______

n Electrons do not move easily through ______.

What are examples of good insulators?

______

How is Electric Charge Transferred?

n Charging by ______

n The process of transferring charge by ______or ______

n Example: ______

n Rubbing two materials together can result in a transfer of ______.

n Then one material is left with a positive charge and the other with an equal amount of ______charge.

Charging by Induction

n Because electrical forces act at a distance, charged objects brought near a neutral object will cause electrons to ______their positions on the neutral object.

n Example: a negatively charged balloon near your sleeve causes an area of your sleeve to become positively charged by ______.

n 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.

n The ______of electrons on a ______object caused by a nearby charged object is called ______.

Static Electricity

n Static ______

– A ______of ______through the air between two objects because of a buildup of ______electricity

– Example: lightning

Lightning

n Lightning is a large ______.

n A static discharge is a transfer of charge between two objects because of a buildup of static electricity.

n 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.

n Eventually, enough charge builds up to cause a static discharge between the cloud and the ground.

n 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.

n Lightning also generates powerful ______.

n The electrical energy in a lightning bolt rips electrons off atoms in the atmosphere and produces great amounts of heat.

n The heat causes air in the bolt’s path to expand rapidly, producing sound waves that you hear as ______.

Electric Charge

n ______– using a ______to direct an electric charge into the ground.

n 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 1

The law of conservation of charge states that ______

______

Question 2

Which of the following is the best conductor of electricity?

______

Question 3

The 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?

n The ______through a wire of conductor is called ______

n Current is usually the flow of ______

n Electric current is measured in ______(___)

n Charges flow from ______voltage to ______voltage

Sources of Electricity

n A ______produces a voltage difference between its ______container and its ______suspension rod, causing current to flow between them

Sources of Electricity

n A ______contains two connected plates made of different ______in a conducting ______

Sources of Electricity

n ______have a voltage difference across the ______of an electrical outlet, and a generator at a ______provides this ______

What is Resistance?

n ______

– ______to the ______of electrons

– electrical energy is converted to ______&______

– all materials have ______electrical resistance

– measured in ______(____)

n Resistance depends on…

– the ______

– ______

n ______resistance in ______wires

– ______

n ______resistance in ______wires

– ______

n ______resistance at ______temps

Ohm’s Law

n 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.

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

n 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

B - switch D - resistor

Example

n Hair dryer plugged into wall outlet

n Generator at power plant produces voltage difference

n Dryer and circuit in house contain conducting wires to carry current

n Hair dryer turns electrical energy into thermal energy and mechanical energy

n Unplug hair dryer opens circuit and breaks path of current

Types of Circuits

n ______circuit – the current has only ______to flow through

n ______circuit – contains ______for current to move through

Series Circuit

n current travels in a ______path

– ______- one ______the flow of current

n current is the ______throughout circuit

– lights are ______brightness

n each device receives a ______of the total voltage

– gets ______as lights are added

n Example: ______

Parallel Circuit

n current travels in ______paths

– one break ______flow

n current varies in ______

– takes path of ______resistance

– “______” light would be dimmer

n each device receives the ______voltage

– ______when lights are added

n Example: ______

Household Circuits

n Combination of ______circuits

– too many devices can cause wires to ______

n Safety Features:

– ______- metal ______, breaking circuit

– ______- bimetallic strip ______when hot, breaking circuit

Household Fuse Box Circuit Breaker Box

Electrical Power

n Electrical Power - rate at which electrical energy is ______to another form of energy P: ______(____)

I: ______(____)

V: ______(__)

Electrical Power

A 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

n Electrical Energy

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

E: ______(______)

P: ______(______)

t: ______(_____)

Electrical Energy

A 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?

How does it work?