- Slides: 26
Electric Charge and Static Electricity
Electric Charge • Electric charge is a property of protons and electrons. • Protons have a positive charge. Electrons have a negative charge. • Electric force is the attraction or repulsion between electric charges. • A magnetic field surrounds a charged object. An electric field is a region around a charged object in which electric force occurs.
Electric Force • Suppose one charged object is placed in the electric field of a second charged object. The first charged object is either pushed or pulled -- repelled or attracted. • The strength of an electric field depends on how far away the charged object is. The farther away a charged object is, the weaker the electric field is.
Static Electricity • Most objects usually have no charge. However, objects can become charged. • If an object loses electrons, it has more protons than electrons. Therefore, it has a positive charge. • If an object gains electrons, it has more electrons than protons. Therefore is has a negative charge.
- + - + + + - + - - Before Rubbing (uncharged) After Rubbing (Negatively Charged) +
Static Electricity • Static Electricity is the buildup of charges on an object. Static means “not moving. ” In static electricity, the charges do not flow or move in the object. • An object becomes charged when electrons transfer from one place to another place.
Transferring Charge • Charging by friction is when electrons move from one uncharged object to another object by rubbing. For example, a girl charges by friction when she runs her socks on the carpet.
Transferring Charge • Charging by conduction is when electrons move from a charged object to another object by direct contact. You can charge yourself by conduction when you touch a charged object. • Think: carpet > socks = friction • Then: socks > feet = conduction • Charging by induction is when electrons move to one part of an object due to the electric field of another object. There is no touching in charging by induction.
Static Discharge • Charges may build up as static electricity on an object. But the charges do not stay on that object forever. • The loss of static electricity as charges move from one object to another is called static discharge. • A static discharge often produces a spark. (Ex: there may be a tiny spark when you touch a metal doorknob. ) • Lightning is another example.
Flow of Electric Charges • Electric current is the flow of electric charges through a material. The charges must flow continuously, or without stopping. • The unit used for the rate of electric current is the ampere. The name can be shortened to amp or A.
Flow of Electric Charges • A current needs a path to follow. An electric circuit is an unbroken path through which electric charges flow. An electric circuit is always a complete loop with no breaks in the loop. • If an electric circuit is complete, charges can flow continuously. If an electric circuit is broken, charges will stop flowing.
Open Circuit Closed Circuit
Features of a Circuit • Circuits have devices (resistors) that are run by electrical energy. • A circuit has a source of electrical energy. • Electric circuits are connected by conducting wires. • These three things are mandatory components of an electric circuit.
Voltage Sources An electric circuit needs a source of energy to have voltage. A voltage source creates a potential difference, or voltage, in an electric circuit.
Often, a switch is placed in an electric circuit. With a switch, you can turn a device on or off by opening or closing the circuit.
Series Circuits • A series circuit has all the parts of the circuit connected on one path. • An example of a series circuit is a circuit with a battery and two light bulbs connected by a single wire. • Suppose a series circuit has two light bulbs. If one burns out, the second bulb goes out because the circuit is broken when the first bulb burns out.
Parallel Circuits • A parallel circuit has more than one path for current to take. There are separate branches in a parallel circuit. Each resistor may be on its own branch. • Suppose a parallel circuit has two light bulbs, each on its own branch. If one light bulb burns out, the other light bulb will stay lit. The second bulb stays lit because it is on its own branch. (Ex: lights in your home, Christmas lights, etc. . )
Electric Power All electrical appliances change electrical energy into another form of energy. For example, a hair dryer changes electrical energy into thermal energy. Power is the rate at which energy is changed from one form to another. The unit of power is the watt, which is abbreviated as W. Each electrical device has a power rating.
The electric company uses giant generators to produce energy for your home and school.
Electric companies send electrical energy through wires at high voltages. Your home, though, uses electrical energy at low voltages. Transformers are used to change the voltage of an electric current.