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Electricity and Magnetism Unit 4 Electricity S8P5: Students will recognize characteristics of gravity, electricity, and magnetism as major forces acting in nature. B. Students will demonstrate the advantages and disadvantages of series and parallel circuits and how they transfer energy. Electric Charge All matter is made up of very small particles called atoms. What are the 2 types of charged particles in atoms? 1. Protons- positively charged particles 2. Electrons- negatively charged particles Parts of an Atom PROTONS Each element on the Periodic Table has a different number of protons. • Protons have a positive charge • Found within the nucleus of the atom • Change the number of protons change element p Parts of an Atom ELECTRONS An element on the Periodic Table has the same number of electrons and protons. • Electrons have a negative charge • Found outside the nucleus in the electron clouds • Change the number of electrons ionize the element (give it a charge) e - Parts of an Atom n NEUTRONS Most elements also have neutrons (except for Hydrogen) • Neutrons have no charge (neutral) • Found in the nucleus of the atom The Law of Electric Charges Law of Electric Charges: like charges repel and opposite charges attract Charges Like charges repel Charges Opposite charges attract Electric Force and Electric Field Electric Force: the force of attraction or repulsion on a charged particle that is due to an electric field The greater the amount of charge, the greater the electric force. The closer the charges are, the greater the electric force. Electric Field: the space around a charged object in which another charged object experiences an electric force Three Ways to Charge an Object Friction: Charging by friction happens when electrons are “wiped” from one object onto another. Conduction: Charging by conduction happens when electrons move from one object to another by direct contact. Induction: Charging by induction happens when charges in an uncharged object are rearranged without direct contact with a charged object. Electrical Potential Energy Electrical charges can be stored on or in objects as potential energy. Examples: Electricity in a battery Rubbing your socks on carpet Electricity in clouds Static Electricity Static Electricity the accumulation of electric charges on an object that are at rest generally produced by friction or induction When something is static, it is not moving. 3 examples of Static Electricity Clothes from a dryer sticking together Balloon sticking to clothes after rubbing it on your hair Negative charges on the bottom of a cloud during a thunderstorm Electric Discharge Electric discharge: the release of static electricity as charges move off an object 2 examples of electric discharge: 1. Walking across carpet and touching a metal doorknob 2. Lightning Electrical Kinetic Energy Electricity electrical energy due to the flow of electrons Electric current the rate at which electric charges pass through a given point (the rate that electrons flow) The greater the flow of charge, the higher the current. Electrons move from negative to positive. Electric charges will always flow from a region of higher potential energy to a region of lower potential energy. The difference in potential energy between two locations is known as potential difference (voltage). Electrical Conductors Electrical conductor: a material in which electrons can move through easily Electrons (e-) are loosely held Examples: Most metals (copper, aluminum, and mercury) Electrical Insulators Electrical insulator a material in which electrons are not able to move easily Electrons (e-) are tightly held Examples: Plastic, rubber, glass, wood, and air DC and AC 2 types of electric currents: DC: direct current AC: alternating current In a direct current, the charges always flow in the same direction (one way). Ex. Dry cell battery In an alternating current, the charges continually shift from flowing in one direction to the reverse direction at regular intervals (two ways). Voltage Voltage the push or force that causes electrons to move from negative to positive a measure of how much work is needed to move a charge between two points • The size of the current depends on the voltage. • The greater the voltage, the greater the current. • A greater current means that more charges move in the wire each second. Resistance Resistance a measure of how difficult it is for electrons to move through a material electrical energy is converted to thermal energy and light (Ex.: a light bulb) You can think of resistance as Copper - low resistance “electrical friction.” A resistor is an object that is added to a circuit that restricts the flow of electrical energy. An object’s resistance depends on its material, thickness, length, and temperature. Good conductors, such as copper, have a low resistance. However, poor conductors, such as Tungsten, have a higher resistance. Tungsten - high resistan Cells Batteries are chemical cells. Batteries convert chemical energy into electricity. A battery can provide the voltage (push) that is needed to keep current flowing in a circuit. • Electric charges are repelled by the negative terminal and attracted toward the positive terminal. Photocells are devices that convert light energy into electrical energy. Ex. Solar panels Electric Circuits: Parts of an Electric Circuit What is a circuit? -a complete, closed path through which electric charges flow Just like a roller coaster, an electric circuit forms a loop; it begins and ends in the same place. All circuits need 3 basic parts. 1. Energy source- provides energy to the circuit; can be a battery, a photocell, or an electric generator at a power plant 2. Wires- connect the other parts of a circuit; made of conducting materials that have low resistance, such as copper 3. Loads- change electrical energy into other forms of energy; examples include light bulbs, appliances, televisions, and electric motors A Switch to Control a Circuit A switch is used to open and close a circuit. In order for loads (like the lights in this classroom) to work, the switch needs to be closed to allow charges to flow through. If a switch is open, the load will not work. Types of Circuits What are the 2 types of circuits? Series circuits Parallel circuits Series Circuit Series Circuit: a circuit in which all the parts are connected in a single loop only one (single) path for charges to follow; so, the charges moving through this circuit must flow through each part of the circuit. Series Circuits: Advantages and Disadvantages Advantages: The bulbs and batteries will last longer. Use less power The current is the same throughout the circuit; therefore, lights shine with equal brightness. Disadvantages Lights get dimmer as more lights are added. • Each device (light bulb, etc.) receives a fraction of the total voltage. • Adding more bulbs resistance goes up, current goes down, and bulbs get dimmer Only one path for charges to flow. • A break in a series circuit causes charges to stop flowing; if one light in a series circuit goes out, the other lights go out, too. Parallel Circuit Parallel circuit – a circuit that has more than one path for the flow of electricity because the parts are joined in branches or multiple loops Parallel Circuits: Advantages and Disadvantages Advantages: The voltage (potential difference) across each part is the same. • Each bulb will glow at full brightness regardless of the number of bulbs. There are multiple paths for charges to travel. • If one bulb breaks, the other bulbs will still work. Disadvantages: The bulbs and batteries will die faster. Use more power The current is not the same in the circuits Household Circuits Combination of parallel circuits too many devices can cause wires to overheat Safety Features: fuse - metal melts, breaking the circuit circuit breaker bimetallic strip bends when hot, breaking the Magnetism and Electromagnetism S8P5. Students will recognize characteristics of gravity, electricity, and magnetism as major kinds of forces acting in nature. c. Investigate and explain that electric currents and magnets can exert force on each other. Magnetism Magnetism The properties and interactions of magnets Due to the arrangement of electrons Closely related to electricity Magnetic Force Magnetic Force Force of attraction or repulsion generated by moving or spinning electric charges Increases as magnets move closer together and decreases as magnets move farther apart Magnetic Poles Magnetic Poles Regions on a magnet where the magnetic force exerted by a magnet is the strongest Like poles repel. Opposite poles attract. A broken magnet creates new poles. Magnetic Field Magnetic Field Area around a magnet where magnetic forces act Magnetic field lines show the direction of the field (NS) Molecular Expressions: Electricity and Magnetism - Interactive Java Tutorials: Magnetic Field Lines Earth’s Magnetic Field Earth’s inner core is made of a solid ball of iron and nickel surrounded by a liquid layer of molten iron and nickel. The circulation of the molten iron and nickel in the Earth’s outer core produces a magnetic field. Therefore, Earth acts like a giant bar magnet. Compass A compass needle is a small bar magnet with a north pole and a south pole. The needle aligns with the magnetic field lines of the Earth’s Magnetic Poles A compass’ needle points to the north geographic pole due to the south magnetic pole being nearby. Magnetic poles are NOT aligned with geographic poles. They Magnetic Domains Magnetic Domains Groups of atoms with aligned magnetic poles Like tiny magnets of different sizes domain In a magnetized object, the domains are all aligned. In a non-magnetized object, the domains are not aligned and cancel each other out. Magnetic Materials Few metals such as iron, cobalt, and nickel are attracted to magnets or can be made into permanent magnets. 69 Types of Magnets Ferromagnets: magnets made of iron, nickel, cobalt, or mixtures of these metals (ex. magnetite) Electromagnets: magnets formed when current passes through a coil of wire (solenoid) surrounding an iron Permanent Magnets Permanent Magnets Magnets that keep their magnetism after they are removed from a magnetic field Keep their magnetic properties longer than temporary magnets Some are made of alnico: an alloy of aluminum, nickel, Permanent Magnets Permanent magnets can be made: Place a magnetic material (iron, cobalt, or nickel) in a strong magnetic field. This causes the magnetic domains in the material to line up. This creates a strong magnetic Temporary Magnets Temporary Magnets Magnets made from materials that are easy to magnetize Tend to lose their magnetism easily Ex. Soft iron items like paperclips and nails Magnetism in Nature aurora borealis aurora australis Auroras They are formed when charged particles from the sun (known as solar wind) hit oxygen and nitrogen atoms in the air. The atoms become excited and then give off many colors of light. The charged particles can crash into the atmosphere at and near the magnetic poles. • North Pole • Northern lights: aurora borealis South Pole Southern lights: aurora Magnetism and Electricity Moving charges, like those in an electric current, produce magnetic fields. Around a currentcarrying wire the magnetic field lines form circles. Magnetism and Electricity As the current in the wire increases, the strength of the magnetic field increases. The direction of the magnetic field around the wire reverses when the direction of the current in the wire reverses. Electromagnetism Electromagnetism The interaction between electricity and magnetism Solenoids Solenoid A single wire wrapped into a cylindrical wire coil that produces a magnetic field when electricity passes through it. If wrapped around an iron core, an electromagnet is formed. Electromagnets Electromagnet A magnet formed when current passes through a coil of wire (solenoid) surrounding an iron core The iron core becomes magnetized only when current flows through the wire. Electromagnets The strength of an electromagnet’s magnetic field can be increased by: Adding more wraps of wire to the solenoid Increasing the current passing through the wire by increasing the voltage. Increasing the size of the iron core Properties of an Electromagnet Has a north and a south pole If placed in a magnetic field, it will align itself along the magnetic field lines Will attract magnetic materials and be attracted or repelled by other magnets Useful because the magnetic properties can be controlled by Electric Motors Electric Motors Devices that convert electrical energy into mechanical energy Electric Motor An electromagnet rotates between the poles of a permanent magnet. Animation Electromagnetic Induction The process in which an electric current is produced in a wire by changing a magnetic field Michael Faraday (1831), a British scientist, discovered this process. An electric current can be produced by moving a magnet through a coil of wire Electromagn etic Induction Electric Generators Electric Generators Devices that use electromagnetic induction to convert mechanical energy into electrical energy Electric Generator Animation As the crank is GENERATOR MOTOR turned, the rotating coil crosses the magnetic field lines of the magnet, inducing a current in the wire. Electric Generators After the wire coil makes one-half of a revolution, the ends of the coil are moving past the opposite poles of the permanent magnet. This causes the current to change direction: • Alternating Current (AC) Electric Generators Examples: Power plants use generators which have many coils of wire wrapped around huge iron cores. The rotating magnets are connected to turbines which are large wheels that rotate when pushed by water, wind, or steam. • Nuclear power plants use thermal energy from a nuclear reaction to boil water into steam in order to turn the turbines. • Wind mills are connected to generators. Electric Generators Example Hydroelectric Dam The Potential Energy (PE) of lake water is converted to Kinetic Energy (KE). Mechanical KE turns the generator shaft which generates