Download little-engineers-09

Voltage, V
• Voltage tells us how hard a positive charge is
pushed between two different points.
• Something, such as a battery, is needed to create
a voltage.
Current, I
• Current tells us the amount of charge flowing through
something (similar to gallons per minute).
• Current must have a path through which to flow.
• Wires provide a path for current flow (and offer no
no resistance to the flow).
What Are These?
+
V
–
Battery
Wires
Switch
Light Bulb
New Symbols
V
+
V
–
Battery
Switch
Old Circuit Drawing
A
Push to
Close
Y
New Circuit Drawing
V
How Much Current Flows?
V
Switch is open.
Zero.
This is an “open circuit.”
How Much Current Flows?
V
Switch is
closed.
TOO MUCH!!!
This is a “short circuit.”
How Much Current Flows?
V
Light bulb has resistance
to flow of charge.
Amount of resistance is
some number R.
Resistor Symbol
R
Electrically: Light Bulb = Resistor
V
V
I
Current, I = V / R
R
LED: A Different Kind of Light Bulb
• LED = Light Emitting Diode
• Current can only flow in one direction
(in direction of arrow).
• Light only emitted when current flows.
• A lot of current may flow if a large
large voltage is across an LED.
Dangerous LED Circuit
V
When switch is closed, too much
current may flow!
Almost behaves as a short circuit.
Need to modify circuit to limit
current…
Good LED Circuit
V
When switch is open, light is off.
When switch is closed, light is on.
Resistor limits current flow.
R
Good LED Circuit
5V0 V
R
GND