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.