Ch. 6 Electricity (Unit 5b) Electric Current Electric Current: the net movement of electric charges in a single direction Measured in amperes (A) 1 ampere = 1 coulomb of electric charge flowing past a point per second (1 C/s) A voltage causes charges to move, which in turn
produces a current. A circuit must be closed for a current to be produced. Open vs Closed Circuit Closed circuit allows electron to flow, lights on Open circuit does not, lights off A charged object has electric PE due to its position in an electric field.
Potential difference or voltage is the difference in electrical PE per unit charge. SI unit for pot. diff. are volts (V). 1 volt = 1 Joule/coulomb Ex. 12V vs. 9V
Conventional electric current flows from higher voltage to lower voltage Voltage sources (like batteries or generators) provide force that causes electric charges to flow _ _ _ _ _ _ _ _ _
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Charge Flow
_ _ _ _ Current Low Voltage _
_ _ _ _ _ _ _ High Voltage
Electric circuit: a closed path that electric current follows Current and Flow Direction is due toofa conventional historical errorelectric The This direction current
always from a higher voltage thatisstuck to a lower voltage, but The electrons in a circuit actually flow from a lower voltage to a higher voltage Resistance Resistance: the tendency for a material to resist the flow of electrons and to convert
electrical energy into other forms of energy Measured in ohms ( ) Caused by internal friction which slows the movement of charges through conducting material Resistor: a special type of conductor used
to control current Resistance Good conductors have low resistance Insulators or poor conductors have high resistance Thicker wires have lower resistance Thinner wires have higher resistance Water works
analogy Water is analogous to charge (electrons) Water flow (total volume passing a point per second) is analogous to current Water works analogy How high the water starts relative to how low it
ends up is analgous to voltage (potential difference) Water works analogy (alternatively, a voltage source (like a battery) can be thought of as a pump. How much pressure the the pump generates is analogous to voltage)
Water works analogy The narrowness of pipe channels, which reduces the total flow (current), is analogous to resistance Water works analogy Water works
analogy Putting it together: Ohms Law V is voltage, in volts (V) I is current, in amperes (A) R is resistance, in ohms ()) V = IR What it means: For a given voltage, if there is lower
resistance, there is more current (flow) For a given voltage, if there is higher resistance there is less current Alternating Current/Direct Current (AC/DC) Many power sources produce alternating current that is continually reversing flow This is the kind of current supplied to US households
Current reversal occurs 60 times per second (60 Hz) Appliances like toasters, fans, and lights often designed to use AC Alternating Current/Direct Current (AC/DC) Current that has a constant flow in a single direction is called direct current Many electronic devices need DC, so in order to
work when plugged in, an AC adaptor is required AC adaptors allow conversion from ACDC Batteries: Ex. DC Source of Dry Cell Voltage Wet Cell Batteries Batteries
Consist of 2 electrodes surrounded by a material called an electrolyte Electrolyte enables charges to move from one electrode to another Chemical reaction occurs when the 2 terminals are connected in a circuit Voltage difference between
these 2 terminals causes a current through a closed circuit Example: flashlight battery Contains 2 connected plates made of different metals or metallic
compounds in an electrolyte The electrolyte is a conducting liquid solution Example: car battery Dry - Cell
Wet - Cell Semiconductor Semiconductors in pure state are insulators. However, as atoms/impurities are added, or become compounds, these materials begin to be able to conduct electric charge.
Schematic Diagram or drawing used to build a circuit. There are two types of circuits. Series: one path for electrons, if one bulb goes out they all do Parallel: more than one path for electrons, if one bulb goes out the rest can still shine
Series and Parallel Schematics Schematic Symbols Battery Switch Wire Ammeter
Resistor Voltmeter Light Bulb Series Circuit Parallel Circuit
Ammeters & Voltmeters Ammeters read current (in A), placed in series with circuit Voltmeters read V, placed in parallel with device/resistor Circuit Breakers and Fuses Too many appliances on at the same time in a home cause
the overall resistance of the circuit to be lowered. Result is a circuit carrying more electrical current than is safe it is Overloaded. Fires can result when this happens. Circuit Breakers act as a switch and open the circuit. Fuses physically break and open the circuit
Power Formula Unit for Electric Power (P) = Watts (Watts) --- Formula: Power = Current x Voltage --- With symbols: P= IV Remember, power is Energy per Time Using higher wattage appliances will use more energy in less time, and be more costly
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