Download Voltage, Current, and Resistance

Chapter 7
Voltage
 The energy difference between 2 places in a circuit
 Measured in volts (V)
 Flows from areas of high voltage to low voltage
 Negative end of the battery = 0 volts
 Anything that uses voltage (light bulb, motor, etc.)
reduces the voltage
:
Voltage cont.
 To add voltage we stack batteries
 If each battery is 9 volts, what is the
total voltage of each stack?
Multimeter
 Black is connected on
the left
 Red is connected on the
right
 Red MUST always lead
back to the positive end
of the battery
Measuring Voltage
 Black on left
 Red on right
 Knob turned to 200 on
the voltage side
 Touch the black probe to
the (-) end of the battery
 Move the red probe to
the numbered spots on
the diagram
Current
 Flow of electric charges, generally through wires
 Measured in amperes (A)
 Current flows from high voltage to low voltage (+ to -)
Types of current
 There are two types of current
 AC (alternating current) – This is the type of current
coming to and from your home
 DC (direct current) – The current of a battery
Currents have a path
 Currents can either follow one path
 Series circuit
 Or they can have more than one path
 Parallel circuit
Measuring Current
 Black on left
 Red on FAR right
 Knob turned to red amps
section
 Keep the red probe
closest to the (+) end of
the battery
 Move the meter to
designated spots
Resistance
 How easily charge flows through an object
 High resistance = not much current
 Low resistance = lots of current
 Electrical devices have resistance
 More devices = more resistance
 Measured in Ohms (Ω)
Short Circuit
 A circuit with an abnormally low amount of resistance
 Example:
 Battery, wire, back to battery
 Creating a parallel path with very low resistance
 Cause high current = DANGER!
Resistance
 Conductors allow charge to flow through them easily
and have little resistance
 Metals (ex. Copper)
 Insulators do not allow charge to flow
 Glass and plastic
Compare to Water
 Wires carry voltage just like pipes carry water
 Current flows just like water
 Resistance affects the flow of water just like it does
electricity
 A jar with a narrow opening has high resistance and
water flows slowly
 A jar with a wide opening has low resistance and water
flows quickly
How are they related?
 If voltage goes up, current goes up
 If resistance goes up, current goes down
 Voltage and resistance determine the amount of
current in a circuit
Ohm’s Law
 This law relates voltage, current and resistance
 We saw how they are related in the previous slide but
how does it look mathematically?
I = V/R
Current
(amps)
Voltage
(volts)
Resistance
(ohms)