Chapter 7 Electricity. An atom is the basic unit of matter and is made of protons, neutrons, &...
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Transcript of Chapter 7 Electricity. An atom is the basic unit of matter and is made of protons, neutrons, &...
Chapter 7Chapter 7
Electricity
Electricity• An atom is the basic unit of matter and is
made of protons, neutrons, & electrons
– protons: + charge
– electrons: - charge
– neutrons: no charge
Electricity• An atom is the basic unit of matter and is
made of protons, neutrons, & electrons
– when atoms contain the same number of protons & electrons they have a neutral charge
– positive charge – occurs when electrons are lost from atoms to other objects
– negative charge – occurs when electrons are gained from atoms of other objects
Electricity• positive charge – occurs when electrons are
lost from atoms to other objects
• negative charge – occurs when electrons are gained from atoms of other objects
Electricity• static electricity – the accumulation of
excess electric charges on an object
– example: as you walk on carpet, some electrons that are loosely held by the carpet are transferred to your shoes creating opposite charges
Electricity• law of conservation of charge – states that
charge can be transferred from object to object, but it can’t be created or destroyed
– similar to the law of conservation of mass or the law of conservation of momentum
ElectricityLike & Opposite Charges
• opposite charges attract
• like charge repel
ElectricityConductors and Insulators
• Electricity is caused by the movement of electrons, from a negative to a positive region
– conductors - materials in which electrons can move through easily
• examples: metals & water
• responsible for shocks when an excess of electrons are transferred from one surface to another, such as from your hand to a doorknob
ElectricityConductors and Insulators
• Electricity is caused by the movement of electrons, from a negative to a positive region
– insulators - materials in which electrons cannot move through easily
• examples: wood, plastic, rubber, & glass
ElectricityTransferring Electric Charge
• charge by contact – the process of transferring charge by touching or rubbing
– causes a transfer of electrons from one object to another, leaving one object with a positive charge and the other one with an equal amount of negative charge
– example: socks being attracted to each other when coming out of the dryer because of rubbing during drying
– touching a door handle and getting shocked
Warmup 12-1-11• What is Electricity?
• What is a Positive Charge?
• What is Static Electricity?
• What is the Law of Conservation of Charge?
ElectricityTransferring Electric Charge
• charge by contact – the process of transferring charge by touching or rubbing
ElectricityTransferring Electric Charge
2.charging by induction – rearranging of electrons on a neutral object caused by a nearby charged object
– example: bringing a negatively charged balloon near clothing and having it cling to the clothing by an electrical force
ElectricityTransferring Electric Charge
3.lightning - caused by a large static discharge of electrons through the air that meet with the positive charge that is built up on the ground
– collisions of atoms and molecules in the air during
– this discharge account for light being given off
Electricity• Lightning
Electricity• Lightning
ElectricityTransferring Electric Charge
4. thunder - sound wave generated by lighting
– the heat from lightning causes air to expand rapidly,
– producing sounds waves that you hear as thunder
Electricity• grounding – a way to transfer any excess
electric charge to the ground before it builds up and creates lightning
– examples: lightning rods, pipes, plumbing fixtures, metal faucets, etc.
Electricity• The presence of electric charges can be
detected by a device called an electroscope
Electricity7.2: Electric Current
• How is it that electrons can move from one object to another or move through an object? The answer lies with a difference in voltage
Electricity• voltage difference – the push that causes
electrical charges to flow through a conductor
– measured in volts (v)
– Just how heat moves from a high temperature area to a lower temperature area, charge flows from a high voltage area to a low voltage area
Electricity• circuit – closed, conducting loop through
which an electric current can flow
– If the circuit is not closed, the electrons would have nowhere to go, just as if a water line broke, the water would not be able to flow through the pipe.
Electricity• electric current – the flow of electric charge
through a wire or any conductor
– electric current is measured in amperes (A)
ElectricityTypes of Batteries
• dry cell - involves a chemical reaction between zinc and a chemical paste that cause the central carbon rod to become positive and the surrounding lower region to become negative
– once the two terminals are connected through a circuit, electricity flows
– these types of batteries are the most common type (in flashlights or calculators)
Electricity• Dry Cell Battery
ElectricityTypes of Batteries
• wet cell - involves two metal plates and typically an acid solution with a “bridge”
– these types of batteries are used in cars
Electricity• resistance – the tendency for a material to
oppose the flow of electrons, changing electrical energy into thermal energy and light
– resistance means, how hard it is to get electricity through
– resistance in measured in ohms ()
– all materials have some electrical resistance
– electrical conductors have much less resistance than insulators
Electricity• resistance – the tendency for a material to
oppose the flow of electrons, changing electrical energy into thermal energy and light
– list some factors that affect resistance in a wire
• Material of the wire, length of the wire, and thickness of the wire
Electricity• Ohms’s Law – a formula that is used to
measure the amount of voltage or current in a circuit
V = I R
– V: voltage (measured in V)
– I: current (measured in amps)
– R: resistance (measured in )
Electricity• Ohms’s Law – a formula that is used to
measure the amount of voltage or current in a circuit
V = I R
• Calculate the voltage difference across a 25- resistor if a 0.3-amp current is flowing through it.