Electricity

What do you think of when you hear the word “electricity”?

What is Electricity?

• Electricity is a type of energy.

• Electrical energy is caused by the movement of electrons.

Atoms

What is Electricity?

• Greek philosophers observed that when they rubbed amber with fur, the amber would attract lint or dust.

• What type of electricity were they observing?

Electrostatics

• The study of static electricity.

• Electricity that does not move through wires.

– The word static means “not moving”

• Charges build up on objects and can jump from one object to another.

Electrostatics

• When an object becomes “charged” by a rubbing process, it is said to possess a static charge.

• Static charge, or static electricity, refers to electric charges that can be collected and held in one place.

When have you experienced static charge?

Charges in an Atom

• Protons are ______________. They DO NOT move. Why?

• Electrons are _______________. They move. Why?

• So, materials are charged by a transfer of __________________.

Charges in an Atom

• All atoms start off neutral (no electric charge)– # of protons = # of electrons

• If an electron is removed from a neutral atom, the atom has a positive charge (the negative charge was taken away)– An atom with more protons than electrons has a

positive charge

• If an electron is added to a neutral atom, the atom has a negative charge (the negative charge was added)– An atom with more electrons than protons has a

negative charge)

Positive or Negative?

Friction

• Friction occurs when two objects rub against each other.

• Results in one object losing electrons and the other gaining electrons

Particle Model of Electricity

• Three states of charge exist: (+), (-), and neutral

• Neutral objects are charged by friction (movement of electrons)

• Charge: an excess or lack of electrons on a material– Creates forces of attraction or repulsion

(+) and (-) _________

(-) and (-) OR (+) and (+) _________

Observation Time

• With a partner, take a balloon and blow it up.

• Rub the balloon on your hair and pull it away slowly.

1. What do you observe?

2. What do you think is happening with the charges of the two materials?

3. Why is your hair still sticking up after you remove the balloon completely?

Current Electricity

Current Electricity

• Current electricity is electricity that moves. It is the most familiar form of electricity as it is used to run all of our electrical appliances, heat and light our homes.

• Current electricity is simply the flow of electrons.

Current Electricity

• Current electricity can only move through conductors. Conductors are substances (generally metals) in which electrons can move freely.

Creating Electricity

• Different sources exist for creating energy:

• Most electricity is created using two basic steps:

– Remove electrons from one location (takes energy)

– Let electrons flow back (releases energy)

• Basically, just converting one form of energy into another form.

Chemical

• Source converts chemical energy into electrical energy.

• A battery generally uses two different types of metals that are surrounded by an electrolyte (some type of acid).

• Due to a chemical reaction within the battery, the anode builds up an excess of electrons (-). This causes an electrical difference between the anode and the cathode (+).

• When the battery is in use, the circuit is closed. The electrons have a path to travel from the anode to the cathode.

Alessandro Volta (1745-1827)

• The first Battery was invented by Alessandro Volta in 1799.

Thermoelectric

• source converts heat energy into electrical energy.

• Metals heated at one end and cooled at other

• Energized electrons flow towards cool side

– Called a thermocouple

Photoelectric

• source converts solar energy into electrical energy.

• Photovoltaic cells are made from semiconductors (ex. Silicon). When light strikes the semiconductor, the energy is absorbed by the material and this absorbed energy knocks electrons loose.

• These loose electrons are now available to use as electricity.

Piezoelectric

• Source converts mechanical energy into electrical energy.

• Some materials polarize when squeezed (various crystals, ceramics, bone)

– Positive and negative charges are separated on either side of the crystal

• A small voltage is produced

Electromagnetic

• Source converts mechanical energy into electrical energy.

• A generator is a simple device that spins a magnet near a coil of wire to create a steady flow of electrons. As the magnetic field passes through the coil of wire, the magnetic field “pushes” electrons causing them to flow as electricity.

• An energy source is needed to turn the generator. Examples include hydro, wind, wood, coal, fossil fuels, and nuclear energy.

https://www.youtube.com/watch?v=rnPEtwQtmGQ

Nuclear

https://www.youtube.com/watch?v=FNNKhE1FNNM

• https://www.youtube.com/watch?v=Z6rilA4uTlQ

Sources of Energy

• https://www.youtube.com/watch?v=20Vb6hlLQSg

• Voltage is the electric force that causes the free electrons to move from one atom to another.

• Measured in volts

• Electric current is the rate of flow of electrons (how much electricity is moving)

• Measured in amps

• A resistor is something that slows down electrons. Resistors are components used to control the current and voltage to protect the device.

• Loads also act as resistors

A battery with 3 cells powers a circuit containing three light bulbs.

Draw a circuit that has a battery (2 cells), a closed switch and a resistor

connected in series.

Draw a circuit that has a cell, an open switch and two light bulbs connected

in series

Series vs Parallel Circuits

One path for electrons to flow

2 or more paths for electrons to flow

Draw a parallel circuit consisting of a 9.0 V electrical source, three resistors, an open switch controlling the electron flow of the entire circuit.

Draw a circuit diagram containing a battery with 4 cells, three pathways with a lamp on each path. Add switches

to control each of the lamps and a fourth switch to control all of the lamps. Show the direction of electron

flow.