ELECTRICITY

Did You Know?

1. Frog legs helped create the first battery. In 1780, an Italian professor of astronomy, Luigi Galvani, noticed that sparks from a machine in his lab made the legs of a dead frog twitch. Galvani performed experiments in which he placed the frog on a metal table and made its leg jump by touching it with different pieces of metal. But it was his fellow scientist, Alessandro Volta, who figured out that the electricity came from the metal, not the frog leg. When he invented the first battery in 1800, Volta used his knowledge about a wet frog leg serving as a conductor of electricity.

2. The power generated by walking on carpet is similar to that of a lightning strike. The big difference is that the number of volts of electricity that lightning discharges is significantly more than the static produced in everyday activities. You can generate about 3,000 volts by walking on carpet and 30,000 volts by taking off a sweater. Lightning strikes discharge 100 million volts.

3. Thomas Edison once used a telegraph to fight a cockroach infestation. Early in his career, Edison worked in a telegraph office that had previously been a restaurant. Here's his description of the problem and his short-lived solution:

• The office ... was literally loaded with cockroaches, who lived between the wall and the board running around the room at the floor. These were such a bother on my table that I pasted two strips of tinfoil on the wall at my desk, connecting one piece to the positive pole of the big battery supplying current to the wires and the negative pole to the other strip. The cockroaches moving up on the wall would pass over the strips, and the moment they got their legs across both strips, there was a flash of light and the cockroach went into gas. This automatic electrocution device attracted so much attention and got a one-half column description in an evening paper, that the manager made me stop it.

4. The power behind "paddles of life." You may have seen a defibrillator in action on a medical TV show. Do you know how it works? When people experience heart trouble, their heart muscles have become disorganized. Instead of working together strongly, the muscles twitch weakly, a process called fibrillation. The electric shock from the defibrillator briefly stops the heart, which allows the muscles to regain their rhythm.

Do You Remember?

• All materials are made of matter.• All matter is made up of atoms.• Atoms have three main parts.• Protons, neutrons, and electrons.

Do You Remember?• Atoms are believed to look like

this…

Do You Remember?• The Three key pieces to the atom are the:

– Protons, neutrons, and electrons

• Protons have a positive charge.• Neutrons have no charge.• Electrons have a negative charge.

Protons (+)Neutrons (0)

Electrons (-)

Found in the nucleus:

Found moving around the outer electron clouds

Do You Remember?

• Based on this picture, if I were to tell you there is only one key piece that can be given and taken, which do you think that is? Protons, Neutrons, or Electrons?

Protons (+)Neutrons (0)

Electrons (-)

Found in the nucleus:

Found moving around the outer electron clouds

Do You Remember?

• Electrons is right! Therefore…• If an object has more protons

(positive charges) than electrons (negative charges) - the object will have an overall charge of positive.

• What would make this possible? What would have to happen? Remember what is the only thing that can move from an atom.

20 + (-5) =

?

-6 + 8 = ?

Do You Remember?

• If an object has more electrons (negative charges) than protons (positive charges) the object will have an overall charge of negative.

• What would make this possible? What would have to happen? Remember what is the only thing that can move from an atom.

5 + (-8) = ?

-15 + 10

= ?

Do You Remember?

• What will be the charge if an object has an equal number of both protons and electrons?

Charge:• Objects begin as neutral.• Neutral means an object has the same

number of electrons as protons, ie…5 e-s and 5 p+s.

• For an object to gain a charge, the object has to gain or lose electrons.

• Therefore, electrons can not be created nor destroyed, only transferred.

• This is known as…• The Law of Conservation of Charge.

•For an object to gain a charge, the object has to gain or lose electrons.

Chapter 7 Section 1

Static Electricity

• Static electricity is when a charge is built up on an object. The charges do not move. This is usually caused by friction. Examples: feet rubbing against the carpet, combing hair, rubbing a plastic strip with a cloth.

Static Electricity

• Static electricity cannot hurt.

• Static electricity does not supply any useful energy.

There are 2 types of charges.

1. Positive2. Negative• Neutral – This

means that there is no net charge on the object. There are equal numbers of + and – charges.

• Opposite charges will attract.

• Like charges will repel.

• Neutrally charged objects are attracted by both + & -.

• This is a very strong force.

Conductors and Insulators

• A conductor is a substance that allows current to flow through it.

• Examples: copper & most other metals, graphite, the human body

Conductors and Insulators• An insulator is a

substance that does not allow current to pass through it easily.

• Examples: plastic, rubber, glass, wood, dry air (winter).

Current Electricity• Current is when the

charges are moving. The movement allows them to do work for us.

• Examples: lightning, a “shock” from a door knob, current in a wire

• This electric current that you see is the movement of electrons.

Challenge:• Use the idea of Conservation of Charge

to explain why after combing your hair your hair may become “flyaway.”

• Both your hair and the comb begin neutral - they have equal numbers of positive and negative charges. Combing causes your hair to lose electrons. All of your hair is then negatively charged - and all like charges repel.

ELECTROSCOPE

• An object that is used to tell if an object has a charge.

• There are two thin metal leaves that hang in the glass jar. When there is no charge, the leaves hang.

ELECTROSCOPE

• When there is a charge, both pieces of metal gain that charge and because like charges repel, the two leaves move apart.