Transcript erpoi
Static Charge and Current: Student Learning Goal The student will be able to distinguish between conventional current and electron flow (D3.6). Static Charge and Current SPH4C Static Electricity The ancient Greeks knew that static charge could be accumulated by rubbing fur on various substances such as amber, which could then attract light objects such a feather. Static Electricity And if they rubbed the amber for long enough, they could even get a spark to jump. hlektron When scientists returned to the subject in the 1600s, they invented the word electricus from hlektron (elektron), the Greek word for amber, to describe the subject. More 17th Century Progress Guericke invented the 1st electrostatic generator: and learned that like charges repel. More 17th Century Progress Boyle (using a generator and Guericke’s other invention, an air pump that can create a partial vacuum) determined that electric attraction and repulsion can act across a vacuum. Conductors and Insulators In 1729, Gray classified materials as conductors (materials that carry charge easily) and insulators (materials that don’t carry charge easily), although he did not invent the terms. But what was this “electricity”? The One-Fluid Theory Benjamin Franklin argued in favour of the one-fluid theory. The One-Fluid Theory Benjamin Franklin argued in favour of the one-fluid theory. The One-Fluid Theory Benjamin Franklin argued in favour of the one-fluid theory: that electricity was a type of fluid present in all matter and an excess of it resulted in positive charge and a deficit of it resulted in negative charge. The One-Fluid Theory Electrons Actually, positive charge results from not an excess of electrical “fluid” but a deficit of electrons, the negatively charged particles on the outside of atoms that can be given enough energy to free them from their atoms. Charging by Friction Electrons may be removed from or added to an object by rubbing it with another object with a different electron affinity. e.g. a rubber rod will acquire electrons, i.e. a negative charge, when rubbed with fur. The fur , which will have lost electrons, will acquire a positive charge. Charge Conduction Charge acquired by friction can then be conducted to an object with a smaller, opposite, or neutral charge. Charge Conduction: Why? Electrons will flow from a charged object to a neutral object because they want to be as far away from each other as possible. They are like charges and like charges repel. Unlike charges (negative electrons and positive nuclei) attract. Charge Quantized Charge (Q) is measured in Coulombs (C). Qelectron e 1602 . 10 19 C Moving Charge We measure the rate at which charge is moving or flowing past a certain point, i.e. Moving Charge We measure the rate at which charge is moving or flowing past a certain point, i.e. current (I), in Moving Charge We measure the rate at which charge is moving or flowing past a certain point, i.e. current (I), in Amperes (A): Q 1C I and 1 A t 1s Moving Charge: Example A lamp uses a 7 W bulb that draws 0.060 A of current. How much charge passes through this bulb in 8.0 hours? Moving Charge: Example A lamp uses a 7 W bulb that draws 0.060 A of current. How much charge passes through this bulb in 8.0 hours? I 0.060 A 60 60 s 28 800 s t 8.0 h 1h Q? Moving Charge: Example A lamp uses a 7 W bulb that draws 0.060 A of current. How much charge passes through this bulb in 8.0 hours? Q I Q It t 3 Q 0.060 A28800 s 17 . 10 C DC and AC Electrons can be induced to flow by a battery, which will force electrons in a single direction, from the negative terminal to the positive terminal. This singledirection flow is direct current, or DC. DC and AC Electrons can also be induced to flow by an electrical generator, which will force electrons in alternating directions. The direction of the electrons changes 120 times a second. This alternating-direction flow is alternating current, or AC. Conventional Current Note: in either case, the direction of conventional current flow is opposite the direction of electron flow. - - + + electrons conventional current Electrical Energy In either case, the electrons flow because they are given energy (measured in Joules) by the battery or generator. The energy per unit charge is called the potential difference, or voltage. Voltage Voltage is measured in Volts (V): E V Q J 1V 1 C Example What amount of energy does it take to move a charge of 2.0 mC across a potential difference of 1.5 V? Example What amount of energy does it take to move a charge of 0.002 C across a potential difference of 1.5 V? E V E VQ Q E (1.5V )(0.002) 0.003 J More Practice Static Charge and Discharge Lab Activity