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Learn the basics of electricity, including electric charges, electric current, and electric circuits. Discover how charges are transferred, the difference between static and current electricity, the role of voltage and resistance, and the properties of conductors and insulators.
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What is a Electricity? • Electricity- the energy associated with charged particles as they move from place to place • While these particles are usually electrons, any charged particles will do
Charges Exert Forces • Electric field- a region surrounding every electric charge in which a force of attraction or repulsion is exerted on the other electric charges • Electric field arrows point away from positive charges and toward negative
Electric Charge • Electric charge- a property of electrons (-) and protons (+) • When particles with these charges come near one another, a force of attraction or repulsion results • Like charges repel and opposites attract
Electric Charge • Electrons in atoms are bound more tightly to some atoms than others • Substances made of atoms with loosely bound electrons can transfer the electrons to substances they come into contact with • Remember that electrons are negatively charged • Protons are stuck in the nucleus
Charge Can Be Transferred By: • 1.) Contact: an object with an excess of electrons touches or rubs a neutral object, electrons are passed to the neutral object • 2.) Induction: the rearrangement of electrons on a neutral object caused by a nearby charged object without contact • Contact vs. induction simulation
Transferring Charges • What causes you to be shocked when you rub your feet across carpet? • The passing of an electrons through the air from a negatively charged object to a positively charge object causes current
Transferring Charges • The Van de Graaf generator deposits electrons on the ball, which travel through the person’s hand touching it • Body and hair temporarily get a negative charge • What up with the hair?
Static Electricity • Static electricity- the accumulation of excess stationary electric charge on an object • Negative charge in cloud builds up and repels that of the ground • The actual flash of lightning you see is the mass of positive ions from the ground surging upward to meet the negative particles • Lightning video
Static Electricity • An electroscope detects static charges
Electric Current • Electric current- the net movement of electric charges in a single direction; represented by “I” and measured in amperes • In a metal wire without current, the electrons are in constant motion in all directions • Stereos, lights, etc. work when electric current is through them • A voltage difference is what causes electric current • Kinetic energymovement!
Static vs. Current Electricity • Static electricity is stationary or collects on the surface of an object, whereas current electricity is flowing very rapidly through a conductor • The flow of electricity in current electricity has electrical pressure or voltage
Voltage Difference • Voltage difference- related to the electrical force that causes charges to flow; represented by “V” and measured in volts • The direction of the current is always from higher voltage (+) to lower voltage (-) but the electrons travel in the opposite direction • Current and voltage applet
Batteries • Batteries are composed of a chemical substance which can generate voltage • There are two kinds of batteries: dry cell and wet cell batteries • This is an example of a dry cell and is called a dry cell because the electrolyte is a moist paste, and not a liquid • One electrode is the carbon rod, and the other is the zinc container
Batteries • Wet cell batteries are most commonly associated with automobile batteries • A wet cell contains two connected plates made of different metals or metallic compounds in a conducting solution
Electric Circuit • Electric circuit- a closed path that electric current follows • In a battery, there is a voltage difference between the two terminals (ends) • Negatively charged electrons flow from the negative terminal of a battery to the positive terminal and the current goes the opposite way
Resistance • Resistance- the tendency for a material to resist the flow of electrons to convert electrical energy into other forms, such as thermal; represented by “R” and measured in Ohms (Ω) • Almost all materials have some resistance • Resistors in electronics are used to reduce current through all or part of a circuit
Resistance • The metal which makes up a light bulb filament has a high electrical resistance which causes light and heat to be given off
What Influences Resistance? • Material of wire • Thickness – the thicker the wire the lower the resistance • Length – shorter wire has lower resistance • Temperature – lower temperature has lower resistance because the atoms of the wire are not moving as much and interferring with flow
Conductors vs. Insulators • Conductor- a material through which electrons move easily because the electrons are not held tightly by the atoms • Metals, skin, solutions • Insulator- a material in which electrons are not able to move easily because the electrons are held tightly by the atoms • Plastics and glass
Ohm’s Law • Ohm’s Law states that the voltage difference (V), current (I), and resistance (R) in a circuit are related • Current (amps) = voltage difference (volts) resistance (ohms) • I = V R Ohm’s Law Interactive
Types of Current • Alternating current (AC)- the kind of current from household electrical outlets in which the current changes direction (120 times/sec in the U.S.) • Direct current (DC)- the kind of current that battery powered devices use in which the current doesn’t change direction
Electric Circuits • There are two types of circuits: • Series circuit- the components are lined up along one path. If the circuit is broken, all components turn off
Electric Circuits • Parallel Circuit – there are several branching paths to the components. If the circuit is broken at any one branch, only the components on that branch will turn off
Electric Circuits • Electrical energy enters the home usually at a breaker box or fuse box and distributes the electricity through multiple circuits • A breaker box or fuse box is a safety feature
Household Circuits • Most household wiring is logically designed with a combination of parallel circuits
Electric Power • Electric power- the rate at which electrical energy is converted into another form of energy • Electrical power is the product of the current (I) and the voltage (V) • The unit for electrical power is the same as that for mechanical power – the watt (W) • Electrical power = current (amps) x voltage (V) • P =IV
Check for Understanding • How much power is used in a circuit which is 110 volts and has a current of 1.36 amps?
Check for Understanding • How much power is used in a circuit which is 110 volts and has a current of 1.36 amps? • P = I V • Power = (1.36 amps) (110 V) = 150 W
Electric Energy • Electric companies provide your house with electrical energy that you can then transform into other forms of energy….thermal (toaster), mechanical (washing machine), etc. • Electric energy = electrical power (kilowatts) x time (h) • E = P x t
Check for Understanding • A microwave has a power rating of 1000 Watts and the family uses it for 30 minutes a day. How much electrical energy has this microwave used?
Check for Understanding • A microwave has a power rating of 1000 Watts and the family uses it for 30 minutes a day. How much electrical energy has this microwave used? • Electric energy = electrical power (kilowatts) x time (h) • E = P x t • 1000 W = 1 kW and 30 minutes = 0.5 h • E = 1 kW X 0.5 h = 0.5 kWh
Check for Understanding • Super challenge! Put it together! • The current flowing through an appliance connected to a 120 V source is 2 A. How many kilowatt-hours of electrical energy does this appliance use in 4 hours?
Check for Understanding • Super challenge! Put it together! • The current flowing through an appliance connected to a 120 V source is 2 A. How many kilowatt-hours of electrical energy does this appliance use in 4 hours? • P = I V = 2 A x 120 V = 240 Watts = 0.240 kW • E = P x t = 0.240 kW x 4 h = 0.96 kWh
Electric Energy • Kilowatt-hours are read on an electric meter and you are charged for each kilowatt-hour by the electric company • It’s the total number of kilowatts used by all appliances times the total number of hours those appliances are used
Magnets • More than 2,000 years ago Greeks discovered deposits of a mineral called magnetite • In the twelfth century Chinese sailors used magnetite to make compasses that improved navigation • Today, the word magnetism refers to the properties and interactions of magnets
Characteristics of Magnets • Every magnet has two poles (N and S) and is surrounded by a magnetic field • This field exerts a force on other magnetic material • Magnetic poles are where the magnetic force exerted by the magnet is strongest • Depending on which ends of the magnets are close together, the magnets either repel or attract each other
What else do you know of that has a North and South Pole? • If you answered Earth you were right! It is one giant magnet with two magnetic poles surrounded by a magnetic field • This field is what causes a compass needle to point in different directions the poles of a magnet to point either north or south • N and S poles do move in time
Magnetic Field Direction • A magnetic field also has direction shown by the arrows • The north pole of a compass points in the direction of the magnetic field • This direction is always away from a north magnetic pole and toward a south magnetic pole
Magnetic Materials • All metal objects are not attracted by magnets • Only a few metal (iron, cobalt, and nickel) are attracted to magnets or can be made into permanent magnets • Every atom contains electrons and these electrons have magnetic properties • These magnetic properties don’t cancel out in magnetic materials
Magnetic Domains • Atoms that have magnetic fields can exert a force on other nearby atoms • This means all the N magnetic poles in the group point in the same direction • These groups of aligned atoms are called magnetic domains • Behave like magnets with a N and S pole • Contain an enormous number of atoms, yet the domains are too small to be seen with the unaided eye
Permanent Magnets • A permanent magnet can be made by placing a magnetic material, such as iron, in a strong magnetic field • The strong magnetic field causes the magnetic domains in the material to line up • The magnetic fields of these aligned domains add together and create a strong magnetic field inside the material • This field prevents the constant motion of the atoms from bumping the domains out of alignment. The material is then a permanent magnet
How are Electricity and Magnets Related? • By the 1700s, scientists everywhere had made many advances in both electricity and the study of magnetism • They then wondered if there was a possible link between the two fields. • The first to discover such a connection was a Danish physicist, Hans Christian Oersted (1777-1851).
Magnets and Electricity • It is now known that moving charges, like those in an electric current, produce magnetic fields • The direction of the magnetic field around the wire reverses when the direction of the current in the wire reverses • As the current in the wire increases the strength of the magnetic field increases
Magnets and Electricity • Magnets are used to generate, or produce, electricity and vice versa • When a conductive wire is wrapped around a piece of metal (like a nail) and current is run through it, magnetism can be induced in the metal • This is called electromagnetic induction
Electromagnets • Electromagnet- a temporary magnet made by passing electric current through a wire coiled around an iron bar • Can see them in junkyards • A crane holding a huge electromagnet can be used to pick up scrap metal when current flows through it • When the crane operator wants to drop the scrap, they shut off the current