Electricity and Magnetism Chapters 17-18

Standard SPS10. Students will investigate the properties of electricity and magnetism. a. Investigate static electricity in terms of friction induction conduction b. Explain the flow of electrons in terms of alternating and direct current. the relationship among voltage, resistance and current. simple series and parallel circuits.

Standard SPS10. Students will investigate the properties of electricity and magnetism. c. Investigate applications of magnetism and/or its relationship to the movement of electrical charge as it relates to electromagnets simple motors permanent magnets

Essential Questions How do electrical and magnetic forces interact and how can this interaction be used in technological design? If electricity flowed like a river current, what would the current, resistance, and voltage be like?

Learning Targets You should know the different types of circuits You should know how to calculate Ohms Law

electrolyte a substance that, in solution or when molten, ionizes and conducts electricity Water is a poor conductor but salt water is a good conductor!

How you should be thinking about electric circuits: Voltage: a force that pushes the current through the circuit (in this picture it would be equivalent to gravity)

Electrical Energy Electricity is a form of energy related to the flow of electrons (small, negatively charged parts of an atom) through a conductor. It is associated with the movement of an electric charge. It is the ELECTRONS that move…..NOT the Protons!!!

Electrical Charge Electrical charge is an electrical property of matter that creates force between objects. The SI unit for charge is a coulomb, C.

Electrical Charge Differences in electric charge come from natural charges that exist within the atom. The nucleus is made of positively charged protons and neutrally charged neutrons. Electricity is associated with the negatively charged electrons moving outside the nucleus.

Electrical Charge An atom is typically neutrally charged because it has the same number of protons as it does electrons. gain of electrons = negative charge loss of electrons = positive charge Objects that have like charges repel each other. Objects with opposite charges attract each other. Charge can created in 3 ways:

Conservation of Charge A charged atom is an ion. positive ion – atom loses electrons negative ion – atom gains electrons Charge is always conserved – never created or destroyed!

Electrical Charge Charging by Friction: Also called static electricity or static charge. Occurs when two objects are rubbed together forcing electrons from one object to be transferred to another. This causes the positive charge of one object and the negative charge of another.

Hair and balloon are neutrally charged. Electrical Charge Hair and balloon are neutrally charged. The balloon and hair become charged when electrons transfer due to friction. Since the hair is now positively charged and the balloon is now has a net negative charge, the balloon and hair attract.

- - - - - - - - - Electrical Charge Van de Graaf generators create electric charge through friction. - - - - - - - - -

Stays neutral even though charges are separated. Electrical Charge Charging by Induction : Caused by the movement of charges within an object. The overall charge of an object is zero, but the opposite sides will be charged. The objects do not have to touch for induction to occur. Stays neutral even though charges are separated.

Electrical Charge Charging by Conduction: Method of charging occurs when electrons flow through one object into another by direct contact.

Electrical Charge Conductors are materials that transfer charge easily. Examples: Materials such as silver, copper, aluminum, and magnesium. Insulators are a material that does not transfer charge easily. Examples: Materials like rubber, glass, silk, and plastic slow or stop the movement of electrons.

Electrical Discharge Electrical discharge relieves a build-up of charges by creating a spark if the object comes in contact with a conductor. Once an object has had an electrical discharge it becomes electrically neutral.

Electric Discharge Lightning is an electrical discharge from a buildup of static electricity in the clouds.

Electric Force Electric force is the attraction or repulsion between objects dues to charge. Create strong ionic bonds in atoms. Affected by: amount of charge distance between charges. Electrical force causes electrons to move.

Electric Force Electric fields are the region around a charged object in which other charged objects experience and electric force.

Ohm’s Law Electric current (I) measures the rate that electric charges move through a conductor. Measured in amperes (A). increased current = increased speed of electricity flow

Ohm’s Law Voltage or electrical potential is the ability to move an electric charge from one point to another. The voltage difference between two points in a circuit is called the potential difference. Measured in volts (V).

Ohm’s Law Voltage tells us how much work a battery can do. More voltage is like a stronger pump, giving more force and more current. To increase voltage you could use a stronger battery OR add batteries.

Ohm’s Law Electrical Resistance is a measure of how much an object opposes the passage of electrons. Measured in Ohms (Ω). Caused by internal friction in a circuit. Resistance slows down electrical current. Adding devices in a circuit increases resistance.

Ohm’s Law A resistor is a material with a high resistance that is inserted into a circuit to increase its resistance. Example: Filament in a light bulb.

Ohm’s Law Differences in resistances: Conductors have low resistances while insulators have high resistances. Below a certain temperature some substances can actually exhibit no resistance (superconductors). Semiconductors have an intermediate resistance between conductors and insulators.

Ohm’s Law Resistance can be calculated using Ohm’s Law: Resistance = voltage/current R=V/I (R – Ohms Ω, V – Volts V, I – Amperes A)

Ohm’s Law Find the resistance of a portable lantern that uses a 24 V power supply and draws a current 0f 0.80 A. V = 24 V R = ? Ω I = 0.8 A R = V / I V I * R R = 24 V / 0.8 A R = 30 Ω

Ohm’s Law The current in a video game is 0.50 A. If the resistance of the game’s circuitry is 12 Ω, what is the voltage of the battery? V = ? V R = 12 Ω I = 0.5 A V = I * R V I * R V = 0.5 A * 12 Ω V = 6 V

Ohm’s Law A 1.5 V battery is connected to a small light bulb that has a resistance of 3.5 Ω. What is the current in the bulb? V = 1.5 V R = 3.5 Ω I = ? A I = V / R V I * R I = 1.5 V / 3.5 Ω I = 0.43 A

Circuits A circuit is one or more complete, closed paths for electron flow. Electricity flows through circuits made of conductors that are connected in a complete loop. (closed circuit). Any break in the circuit will cause the circuit to fail (open circuit). Open Closed

Circuits A schematic diagram is graphic representation of an electric circuit with standard symbols for the electrical devices. The electrons leave the battery from the negative terminal and travel to the positive terminal.ALWAYS!

Circuits When the electric charges in a circuit have only one path in which to flow, the circuit is called a series circuit. If one light bulb goes out, they all go out! Flow Interrupted

Circuits If the circuit has different branches in which the electric charges can flow, the circuit is called a parallel circuit. Parallel circuits also reduce the total resistance making the lights brighter. No Interuption

Circuits

Circuits A short circuit can occur if a wire’s insulation breaks down and two wires touch and create an alternate pathway. Circuit breakers and fuses help prevent this.

Circuits Electric Power is the rate at which electrons are moved across a circuit. Electric companies use electric power to charge you for your electricity used (kW / h).

Ohm’s Laws in Series Circuits The total voltage (VT) is calculated by adding all of the voltages in the circuit. VT = V1 + V2 + … VT = 6 V + 6 V VT = 12 V

Ohm’s Laws in Series Circuits The total resistance (RT) in a is calculated by adding all of the resistances in the circuit. RT = R1 + R2 + … RT = 4 Ω + 1 Ω + 1 Ω RT = 6 Ω

Ohm’s Laws in Series Circuits The total current (IT) is calculated by using Ohm’s Law. IT = VT / RT IT = 12 V / 6 Ω IT = 2 A

Ohm’s Law in Parallel Circuits The total voltage (VT) is calculated by adding all of the voltages in the circuit. VT = V1 + V2 + … VT = 1.5V + 1.5 V VT = 3V

Ohm’s Law in Parallel Circuits VBranches = VT VT = 3 V VB1 = 3 V VB2 = 3 V 3 V 3 V

Ohm’s Law in Parallel Circuits Use Ohm’s Law to find the I in each branch: Branch 1: I1 = 3 V / 1 Ω I1 = 3 A Branch 2: I2 = 3 V / 1 Ω I2 = 3 A 3 V 3 V 3 A 3 A

Ohm’s Law in Parallel Circuits IT = I1 + I2 + … IT = 3 A + 3 A IT = 6 A 3 V 3 V 3 A 3 A 6 A

Ohm’s Law in Parallel Circuits Use Ohm’s Law to find the total resistance (RT): RT = VT / IT RT = 3 V / 6 A RT = 0.5 Ω 3 V 3 V 3 A 3 A 6 A

Ohm’s Law in Parallel Circuits The total resistance (RT) in a parallel circuit is can also be calculated by adding the inverses of the resistances in the circuit. 1/RT = 1/R1 + 1/R2 + 1/R3 + … 1/RT = 1/1Ω + 1/1Ω 1/RT = 2/1 (Take the inverse to find the answer!) RT = 1/2 or 0.5 Ω 3 V 3 V 3 A 3 A 6 A

Magnets A magnet is a device made of a ferromagnetic metal (typically iron or nickel) that gives off a magnetic field. Magnets are created due to the alignment of several small magnetic fields in a magnetic material called domains. Non Magnet Magnet

Magnets Permanent magnets: never lose their magnetism. Temporary magnets: lose their magnetism over time Magnets can be man- made, but the first magnets used were natural (ex. lodestone, magnetite)

Magnetic Fields A magnetic pole is an area of a magnet where the magnetic force appears to be strongest. There are two types: North Pole South Pole

Magnetic Fields Unlike magnetic poles (south pole- north pole) will attract each other while like magnetic poles (north pole- north pole) repel each other.

Magnetic Fields A magnetic field is a region around a magnet or current- carrying wire where magnetic forces can be measured. Magnetic fields come out of the north pole and into the south pole.

Magnetic Fields Compasses are a magnet suspended on top of a pivot so that the magnet can rotate freely. Compasses can track magnetic fields.

Magnetic Fields The Earth’s geographic “North” and “South” poles are different from Earth’s magnetic poles. The geographic poles are straight up and down versus the magnetic poles that are slightly tilted (magnetic north is in Canada).

Magnetism and Electric Current A solenoid is a coil of wire with an electric current in it. The electric current creates a magnetic field around each loop of the wire. more loops = more magnetic force more current = more magnetic force

Magnetism and Electric Current The magnetic force of a solenoid can also be strengthened by adding a soft iron core to its center. This is called an electromagnet.

Creating Electric Current Faraday’s Law of Induction describes the production of a current in a conducting circuit by a change in the strength, position, or orientation of an external magnet.

Creating Electric Current Electrical generators change mechanical energy to electrical energy using electromagnetic induction. In a commercial generator, an electric current is produced when a large coil of wire is rotated through a strong magnetic field.

Creating Electric Current Electrochemical cells change chemical energy into electrical energy. Electrochemical cells “batteries” contain an electrolyte (a solution that conducts electricity) and two electrodes, each a different conductor.

Types of Batteries There are two types: Dry Cell: (contain electrolyte paste) Wet Cell (contains electrolyte liquid)

Creating Electric Current Electricity from a generator changes direction moving back and forth in cycles. This is called alternating current (AC). Electrochemical cells have direct current (DC) which means that the charges always move in the same direction through a circuit.

Using Electric Current Electric Motors convert electrical energy into mechanical energy by using magnets to create motion. Inside an electric motor, the attracting and repelling forces of two magnets create a rotational motion.