Electric Current The amount of charge that moves past a given point in a conductor per second. The amount of charge that moves past a given point in a conductor per second. I = q I = q t I = current (amperes) q = quantity of charge (coulombs) I = current (amperes) q = quantity of charge (coulombs) t = time (seconds) t = time (seconds) Ampere is the amount of current when one coulomb of charge moves by a point in a conductor in one second. Ampere is the amount of current when one coulomb of charge moves by a point in a conductor in one second.

Calculate the amount of current through a toaster if it takes 900 coulombs of charge to toast two slices of bread in 1.5 minutes. Calculate the amount of current through a toaster if it takes 900 coulombs of charge to toast two slices of bread in 1.5 minutes. Given Given t = 1.5 minutes = 90 seconds q = 900 coulombs q = I 900 Coulombs = 10 C/s or amps t 90 seconds

Measuring devices

Electric Potential When charges are in the presence of an electric field they have potential energy. When charges are in the presence of an electric field they have potential energy. The charges position in the electric field determines how much potential energy that charge will have. The charges position in the electric field determines how much potential energy that charge will have. Remember like charges repel and opposite charges attract. Remember like charges repel and opposite charges attract. Two charges will have potential energy between them just like objects possess potential energy when they are raised above the earth’s surface. Two charges will have potential energy between them just like objects possess potential energy when they are raised above the earth’s surface.

Potential Difference and Voltage Moving charges in an electric field requires work. Moving charges in an electric field requires work. Voltage is the potential difference. Voltage is the potential difference. Voltage = work (change in potential energy) Voltage = work (change in potential energy) charge charge Joules/Coulomb = Volt

One volt is the electric potential difference between two points if it takes 1 Joule of work per coulomb to move a positive charge from one point to another. One volt is the electric potential difference between two points if it takes 1 Joule of work per coulomb to move a positive charge from one point to another. 1 volt = 1 Joule per coulomb 1 volt = 1 Joule per coulomb A 12 volt battery means that 12 Joules of work is done on each Coulomb of charge that flows through it. A 12 volt battery means that 12 Joules of work is done on each Coulomb of charge that flows through it. As charges flow through conductors they lose potential energy. As charges flow through conductors they lose potential energy.

The electrical energy lost or work done by a charge traveling through a conductor can be calculated. The electrical energy lost or work done by a charge traveling through a conductor can be calculated. E = qV like ΔPEg = Δmgh E = qV like ΔPEg = Δmgh E = energy lost or change in energy. (Joules) E = energy lost or change in energy. (Joules) q = charge (Coulombs) q = charge (Coulombs) V = potential difference (voltage) V = potential difference (voltage) q =It substituting It for q in E =qV q =It substituting It for q in E =qV E = ItV E = ItV E = energy lost (Joules) E = energy lost (Joules) I = current (amperes) I = current (amperes) t =time (seconds) t =time (seconds) V = voltage (volts) V = voltage (volts)

Sources of Current Batteries Batteries Provide a source of electrons through a chemical reaction. Provide a source of electrons through a chemical reaction. Voltaic Cells Voltaic Cells Two metal strips called electrodes create ions when submerged in acid (electrolyte) Two metal strips called electrodes create ions when submerged in acid (electrolyte) Since they are two different metals a deficit of electrons is created at one electrode and a surplus of electrons is created at the other electrode. Since they are two different metals a deficit of electrons is created at one electrode and a surplus of electrons is created at the other electrode. When these terminals are connected by a wire, the electrons flow from one electrode to the other. When these terminals are connected by a wire, the electrons flow from one electrode to the other.

Batteries Dry cells (Duracell, Energizer etc..) Dry cells (Duracell, Energizer etc..) Two electrodes are used, carbon and zinc, in a moist paste of ammonium chloride (electrolyte). Two electrodes are used, carbon and zinc, in a moist paste of ammonium chloride (electrolyte). Easier to handle Easier to handle Create 1.5 Volts Create 1.5 Volts Can connect several together to increase the voltage. Can connect several together to increase the voltage. Problem with voltaic and dry cell batteries is when the electrolyte is used up the battery no longer functions. Problem with voltaic and dry cell batteries is when the electrolyte is used up the battery no longer functions.

Solution Secondary or rechargeable batteries Secondary or rechargeable batteries The chemical mixture used can be reversed when current is applied. The chemical mixture used can be reversed when current is applied. The chemical reactants are restored. The chemical reactants are restored. Nickel and cadmium are commonly used in toys Nickel and cadmium are commonly used in toys

Electromagnets Electromagnetic generators Electromagnetic generators Moving a wire through and electric field generates current. Moving a wire through and electric field generates current. Called electromagnetic induction. Called electromagnetic induction. Powered by water, nuclear plants, geothermal steam or burning coal. Powered by water, nuclear plants, geothermal steam or burning coal.

Other Sources of Current Piezoelctricity Piezoelctricity Pressing on piezoelectric material induces small charges. Pressing on piezoelectric material induces small charges. Phonograph needles connected to a piezoelectric crystal pick up vibrations due the grooves in a record and theses vibrations are amplified. Phonograph needles connected to a piezoelectric crystal pick up vibrations due the grooves in a record and theses vibrations are amplified. Thermocoupling Thermocoupling A device that uses different metals attached to a loop of wire to create electrcity when heated. A device that uses different metals attached to a loop of wire to create electrcity when heated. Photoelectricity Photoelectricity The photoelectric effect. Einstein used light to cause metals to release electrons. The photoelectric effect. Einstein used light to cause metals to release electrons. Solar cells Solar cells Semiconductors with a “wafer like” material is treated to form a junction. When the junction is exposed to light a small electric potential difference is created. Semiconductors with a “wafer like” material is treated to form a junction. When the junction is exposed to light a small electric potential difference is created.

In order for current to flow through a conductor there must be a electrical potential difference or voltage present. In order for current to flow through a conductor there must be a electrical potential difference or voltage present. This difference in potential causes charges to flow from a high electric potential to a lower electric potential. This difference in potential causes charges to flow from a high electric potential to a lower electric potential. The amount of current that flows through a conductor depends on the voltage and the material in which the conductor is made of. The amount of current that flows through a conductor depends on the voltage and the material in which the conductor is made of.

Ohm’s Law Relates current, voltage and resistance. Relates current, voltage and resistance. V = I RV= voltage (volts) V = I RV= voltage (volts) R = resistance (ohms) I = current (amperes) Resistance Resistance Property of a material that inhibits the flow of charge. Property of a material that inhibits the flow of charge.

Resistance Factors that affect the resistance of a conductor: Factors that affect the resistance of a conductor: Length of the wire Length of the wire Longer wires pose more resistance than shorter ones. Longer wires pose more resistance than shorter ones. Width of the wire Width of the wire Narrow wires introduce more resistance than wider wires. Narrow wires introduce more resistance than wider wires. Composition of the material Composition of the material Temperature Temperature Higher temperatures introduce more resistance than lower temperatures. Higher temperatures introduce more resistance than lower temperatures.

Electric Power The rate at which electrical potential is converted to other types of energy. The rate at which electrical potential is converted to other types of energy. Electric to light energy - light bulb Electric to light energy - light bulb Electric to mechanical energy – motor Electric to mechanical energy – motor Power = Current x Voltage Power = Current x Voltage P = IV P = IV P = power (watts) P = power (watts) I = current (amperes) I = current (amperes) V = voltage (volts) V = voltage (volts)

Voltmeters must always be connected in parallel

Ammeters must always be connect in series