Transcript Electricity - MWMS HW Wiki

Electric Charges and Static
Electricity
 Two types of charges are positive and negative. ( + - )
 Static electricity is the build up of charges on an object.
These charges do not flow continuously.
 Positive charged particles are called protons, negative charged particles are
called electrons and neutral particles are called neutrons. These particles
make up the atom (smallest particle of matter)
 If an object gains electrons, its charge becomes negative.
 If an object loses electrons, its charge becomes positive.
Electric Current
 Electric current is the continuous flow of
electric charges (electrons) through a
material.
 Current is measured in amps, amperes, or A
using an ammeter.
Electric Circuit
 To produce electric current, charges must flow
continuously from one place to another
 An electric circuit is a complete, unbroken
path through which electric charges can flow.
Features of a Circuit
 All electric circuits have the same basic features.
 First, circuits have devices that are run by
electrical energy.
 Ex: Light Bulb, Radio, Computer
 These devices are also called resistors,
because they resist (slow down) the flow of
electric current and may be shown as a resistor
in a circuit diagram:
Features of a Circuit
 Second, a circuit has to have a voltage
source. Voltage is the difference in
electrical potential energy between two
places in a circuit. It’s measured in volts (V)
using a voltmeter.
 Ex: Batteries and Generators
Features of a Circuit
 Third, electric circuits are
connected by conducting
wires.
 They allow charges to flow
from the voltage source to
the device that runs on
electric current and back to
the energy source
Features of a Circuit
 A switch is often included in a circuit to
control the current in the circuit.
 Using a switch, you can turn a device on or
off by closing or opening the circuit.
Circuit Diagram
Conductors and Insulators
 Conductors are materials through which charges can flow
easily. The atoms in conductors contain electrons that are
loosely bound. Examples: Copper and Aluminum
 Insulators are materials through which charges cannot
flow easily. Their electrons are bound tight to their atoms.
Examples: Rubber and Glass
Resistance
 Resistance is the measure of how difficult it is for charges
to flow. Resistance is measured in ohms, or omega.
 There are four factors that determine the resistance in any
wire. They are:
 Materials (conductors have less resistance than insulators)
 Length (short wires have less resistance than long wires)
 Diameter (thick wires have less resistance than thin wires)
 Temperature (cold wires have less resistance than hot
wires)
Series Circuits
 Only one path for current to take
 If one bulb is removed or goes out, all bulbs go out
 Lights become dimmer as more bulbs are added (more
resistance)
Parallel Circuits
 There are multiple pathways for current to take
 If one bulb is removed or goes out, the other bulbs remain
lit
 Lights remain the same brightness as more bulbs are
added (less resistance)
Electrical Safety
 Circuit Breaker – a safety device that uses an electromagnet to shut off when
current gets too high
 Fuse – a safety device that contains a thin strip of metal that melts when
current gets too high
 Grounding– A circuit is electrically grounded when charges are able to flow
directly from the circuit into Earth in the event of a short circuit
Ground Wire
Ohm’s Law
 Resistance = Voltage / Current
 Problem #1: A toaster is plugged into a 120-volt socket. If
it has a current of 0.25 amps in its coils, what is the
resistance of the toaster?
 Problem #2: The voltage of a car battery is 12 volts. When
the car is started, the resistance is 0.30 ohms. What is the
current of the battery?
 Problem #3: Is a circuit, there is a bulb with a resistance
measuring 8 ohms. The current in the bulb is 0.5-A. What is
the voltage in the circuit?