1. magnetism               9. resistance
                                                      2. magnet                   10. volt
                                                      3. magnetic field          11. current
                                                      4. permanent magnet   12. Ohm's law
                                                      5. compass                 13. wet cell
                                                      6. circuit                      14. dry cell
                                                      7. conductor                15. battery
                                                      8. insulator                  16. ampere
 
 

MAGNET - any object that has a magnetic field and is able to exert forces on other magnets.

MAGNETIC FIELD - area of magnetic lines of force.
 
 
 
 
 
 
 
 
 
 
 
 

PROPERTIES OF MAGNETS:
 

1. attracts certain materials (iron, cobalt and nickel)
2. have two poles - North and South;  the pole which always turns to point toward magnetic north is the north pole, the other pole is called the south pole.

The needle on a compass is a magnet mounted on a pivot.

COMPASS- a suspended magnet with one end pointing toward earth's magnetic north pole.

3. like poles of a magnet repel and unlike poles attract

Magnets have 2 poles The magnetic field is the region where magnetic effects are observed.

NOTE: Due to the magnetic field of force that is around each magnetic, each magnet exerts a force on other magnets. The closer the poles the greater the force.
 

lodestone- is a rock that is a natural magnet. Some materials (ex. alloys of iron, nickel, cobalt) can be made into magnets called permanent magnets. These remain magnets for a long time.
 
 

Types of Electricity:
 

1. Static Electricity- (not moving) built up in one place.

NOTE: Electrons can move through metals and electrolyte solutions OR when two objects are rubbed together; also, electrons can move from one object to another. The object that gains extra electrons becomes negatively charge, the one that loses electrons becomes positively charged.

Objects become electrically charged when they gain or lose electrons, this built-up charge is static electricity.

REMEMBER: Like charges repel each other, unlike charges attract. A wool sock and a cotton sock would cling together because these pieces of clothing have gained electric charge by rubbing against each other.
 

2. Current electricity- the flow of electrons.

NOTE: the obvious difference between current and static electricity is that current electricity moves through a conductor (wire).
 
 
 
 
 
 
 
 
 
 
 
 
 
 

A flow of electrons can be:

1. Alternating Current (A.C.)- the current flows back and forth in the circuit. (from power company)

2. Direct Current (D.C.)- the current flows in one direction in the circuit. (from batteries)
 
 

CONDUCTOR- materials that easily allow an electrical charge to move through.
Example: Most metals are good conductors. Good conductors include silver, copper, & aluminum.

INSULATOR- materials that are poor conductors, they do not allow charges to move through easily.
Examples: plastic, rubber, glass, dry air, silk
 
 

NOTE: Electricity usually flows through a conductor from a source of energy to a device that uses the electric energy. The path followed by the conductor for the electrons is referred to as a circuit.

CIRCUIT- The path formed by the conductors for the electrons.
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Types of circuits

A. Series circuit - the current is the same through each part. If the circuit is broken, the current in all parts is stopped. Example:  When a string of Christmas lights goes out because only one bulb is burnt out.
 
 
 
 

Series
Circuits
 
 

Parallel
Circuits
 
 

BATTERY- acts like a "pump" that forces electrons through a conductor. The simplest batteries consist of one cell, usually batteries contain several cells.

    A. Wet cell- contains two different metals in a solution containing an electrolyte (a liquid that conducts         electricity).

    B. Dry Cell- contains a carbon rod set in the middle of a zinc can, a moist paste fills the can. Chemicals in the paste react with the zinc and release electrons. These electrons flow through a conductor such as a flashlight bulb connected to the dry cell.

NOTE: When a conductor is connected to a battery, current always flows in one direction (direct current, D.C.).
 
 

OHM'S LAW - explains the relation ship between voltage (V), Current (I), and resistance (R). current (I) is equal to the potential difference (voltage) divided by the resistance.

                                                                         V (voltage)   =  I (current)
                                                                                                R (resistance)
 

Current is measured in amperes.

NOTE: Electric current is the movement of charge. The rate of flow of charges particles is measured in amperes (A).

one ampere- flows when one coulomb of charge moves through a conductor in one second.

one coulomb- is the charge on 6.24 billion billion electrons.

The total amount of potential energy difference (voltage)  depends on the number of electrons leaving the battery. The potential energy difference per unit charge is called the electric potential or voltage. The volt is the unit of electric potential.

VOLT (V) - a volt is one joule of potential energy per coulomb of charge.

The difference in potential between electrons in one place and electrons in another place is called potential difference or voltage.

RESISTANCE - a measure of how difficult it is to move electrons through a conductor. Resistance is measured in ohms.
 
 

Sample problem (Ohm's Law):

What value of current flows through a conductor having resistance of 84 ohms connected across a 12-volt battery?

Solution:
V =12V                  if V = IR, then I = V/R;  I = 12 V / 84 ohms = 0.14 amps
R 84 ohms
 
 

Solve the following problems:

1. Find the current through a 25 ohm resistor connected to a 12-volt battery.

2. A light bulb with a resistance of 180 ohms is connected across a source having a 120-volt potential difference. What current flows?

3. A current of 5.0A flows through a toaster connected to a 110V source. What is the resistance of the toaster? Solve for resistance.