Chapter 7 Electricity

Charge comes from Parts of the Atom

– Nucleus (middle)• Protons – positive• Neutrons – neutral

– Outside• Electrons – negative

• It is the electron that is free to move & causes electricity

How charges interact Opposites Charges Attract & Like Charges

Repel

Neutral and charged objects• Any charged object - will have an attractive force on

a neutral object. • Positively charged objects attract

Neutral objects

• Negatively charged objects also attract Neutral objects

Types of electricity• Static electricity is stationary or the build up of charge on

the surface of an object

• Current electricity is the flow of electrons through a conductor.

– Flows from high to low voltage

Conductors vs. Insulators• Conductor: a material that allows

electric current to pass.

–Metals are good conductors

• Insulator: a material that doesn’t allow electric current to pass.

–Plastic, glass, wood, and rubber are good insulators

dry cell contains a moist chemical paste surrounding a carbon rod suspended in the middle.

Ex. AA, AAA, C, etc

Batteries• Batteries: Devices that converts chemical energy

to electricity. A battery provides a voltage source.

wet cell contains two connected metal plates in a conducting solution.

Ex. Most car batteries

Charging by Contact• Transfer charge by touching or rubbing•Leaves one object with a (+) charge and the other with (-) charge•Ex. Rubbing feet on ground builds up charge.

Charging ObjectsCharging by Induction• Rearrangement of charge on a neutral object by a nearby charged object•Ex. Touching something after charge was built up *SHOCK*

Electric circuits: contain a power source, wires, and devices that use the electrical energy.

Series circuit: provides a single pathway for current to flow. If the circuit breaks, all devices using the circuit will fail.

Ex. Cheap Christmas Lights

Parallel circuit: has multiple pathways for the current to flow. If the circuit is broken the current passes through other pathways and other devices will continue to work.Ex. Homes, cars

Voltage Difference (V)• Voltage Difference—or just voltage (V): force

that causes electric charges to flow– supplied by a battery or other power source.– Potential Difference is measured in Volts named in

honor of Alessandro Volta

Electric Current (I)• Electric Current (I): the rate or the flow of

electrons in a circuit–measured in amperes (amps)

Resistance (R)• Resistance (R): the opposition to the flow of electric

current, causing the electrical energy to be converted to thermal energy or light.

–Measured in ohms Ω

Ohm’s Law

V = I • RVoltage Difference = Current • Resistance

Units: Volts = amps • Ω (ohms)

German physicist Georg Simon Ohm (1789 - 1854).

Series or Parallel Questions1. The current is the same throughout.2. The total resistance is equal to the sum of the

individual resistances. 3. The voltage drop is the same across each resistor.4. The voltage drop is proportional to the resistance.5. Adding resistors decreases the total resistance.6. If the current through one resistor goes to zero, there is

no current in the entire circuit.7. If the current through one resistor goes to zero, the

current through the other resistors remain the same.8. This form is suitable for house wiring.