Download Electric Current and Ohm`s Law Guided Notes

Electric Current and Ohm’s Law Guided Notes
Name_____________________
Electric Current
Current = _________________________
Symbol:
Unit:
1A = 1 C / s
To have an electric current, you need two things:
• A closed circuit / path for the charges
• A power supply maintain the potential difference
Remember: Current will flow from high potential to low potential, but charges need to be
pushed (by an energy source) back from low potential to high potential.
Closed vs. Open Circuits
Direction of Current
Current is defined as the direction __________________ charges would flow
• From high potential to low potential
• From + side of battery to – side of battery
Fun fact: Benjamin Franklin defined current in this manner long
before we knew much about charges.
Now, we know that positive charges stay put and negative charges
flow. So, electrons actually flow opposite current.
Calculating Current
Current is the rate of charge flow per unit time
I=
𝑄
𝑡
So, if you have 6 C of charges passing through a section of wire every 2 seconds, then your
current is: _________________
An important note about current:
Although potential decreases across a circuit, current is the same everywhere in a circuit!
Electrical Resistance (R)
• Electrons to flow due to potential difference. If the potential difference is removed,
current stops
• As electrons move, they bump into other atoms, this slows them down and impedes
their motion.
Resistance (R) is a measure of the degree to which a object __________________________.
Resistance is measured in Ohms ()
Ohm’s Law: Current, Voltage, and Resistance
Current = the potential difference applied across a circuit divided by the total resistance of the
circuit.
• If a 3 volt flashlight bulb has a resistance of 9 ohms, how much current will it draw?
• If a light bulb draws 2 A of current when connected to a 120 volt circuit, what is the
resistance of the light bulb?
• Which of the following would cause the current in a circuit to decrease the most?
•
•
•
•
Increased voltage and increased resistance
Increased voltage and decreased resistance
Decreased voltage and decreased resistance
Decreased voltage and increased resistance
• If the resistance of a circuit were tripled, then the current through the circuit would be
____.
• one-third as much
• three times as much
• unchanged
• nonsense! There would be no way to make such a prediction.
human body resistance varies:
100 ohms if soaked with salt water;
moist skin - 1000 ohms;
normal dry skin – 100 000 ohms,
extra dry skin – 500 000 ohms.
What would be the current in your body if you touch the terminals of a 12-V battery with dry
hands?
But if your hands are moist and you touch 12 V battery, how much current would you draw?