Current Electric Current: (I) the net movement of electric charge in a single direction. Measured in Amperes (Amps) How do the e- move? They travel like a bunch of bouncy balls thrown down a staircase. Fun fact: 1 ampere = 6.24 x 1018 electrons flowing past a point EVERY SECOND! 6.24 x 1018 = 6,240,000,000,000,000,000 (can be read as 6,240 million billion e-)

Voltage Difference Voltage Difference: (V) the push (force) that causes charge to move. Measured in Volts (V) Charge flows from high voltage areas to low voltage areas. So the larger the difference, the greater the current. I like to compare voltage difference to a slide. The steeper the slide (the greater the voltage difference) the higher the “flow” of current

Current Circuit: a closed path an electric current flows through. Necessary in order for electric charge to move. Key part of circuit… know what it is? If switch is open, current will not flow. If switch is closed, current will flow.

Batteries Battery: a device that converts chemical energy to electrical energy. Chemical reactions provide a voltage difference between the (+) and (-) terminals of the battery. When the terminals are connected, an electrical current pushes through the conductor/wire because of the voltage difference. e- flow from the (-) end to the (+) end.

Resistance Resistance: (R) the tendency of a material to oppose the flow of electrons through it. Measured in Ohms (Ω) Affected by 4 factors: Material Insulators have more resistance than conductors. Size of the wire Smaller diameter wire has more resistance. Length of wire Longer wire has more resistance. Temperature of wire Higher temperature has more resistance. To transition to this slide I explain how current doesn’t always flow easily! That’s where resistance comes into play.

Ohm’s Law Ohm’s Law: the amount of current is directly proportional to the voltage difference. The higher the voltage, the higher the current. The lower the resistance, the higher the current. V = IR Current (flow) depends on the voltage difference and resistance. The greater the voltage difference the greater the flow, because there is a stronger push to move more electrons through. The lower the resistance the greater the flow because resistance causes some energy to be converted to thermal energy. I know Ohm’s Law is traditionally written as I = V/R, I just always write it this way because it is simpler for students to rearrange to isolate different variables from here. V = voltage difference Measured in V I = current Measured in Amps R = resistance Measured in Ω

Example #1 V = 7.5 V V = ? I = 0.75 amps R = 10 Ω V = (.75)(10) V = IR What is the voltage difference that flows through a copper wire if a current of 0.75 amps is flowing through it? The resistance of the wire is 10 Ω. V = ? I = 0.75 amps R = 10 Ω V = (.75)(10) V = 7.5 V V = IR

Practice Time A fan is drawing 2 amps and has 4.5 ohms of resistance, what is the voltage of its power source. What is the current produced with a 9 V battery through a resistance of 100 ohms? An electric toothbrush operates on 120 V and has a current of 0.0125 amps. What is its resistance? Answer: V = 9 V I have students work these out in their notes and I walk around and help them as they work. Then we go over the answers all together. I especially encourage CP students that if they don’t know what to do, they at least need to set up the problem (labeling values that they know and writing the appropriate equation.) They should NEVER leave a problem blank! Answer: I = 0.09 amps Answer: R = 9.600 Ω