CAUTION! Do not leave any circuit connected longer than
necessary to observe bulb brightness. Leaving a circuit connected
for too long can ruin the battery (and is not environmentally
friendly).
Slide 3
Stuff to do Make a bulb light with 1 bulb, 1 battery, and 1
wire What do we need to make the bulb light? What doesnt work?
Complete Circuits
Slide 4
Stuff 2 do Conductors and Insulators Look inside a bulb what is
connected to which other parts? How is this similar to a complete
circuit idea from before?
Slide 5
Stuff 3 do Flashlights Switches
Slide 6
What does it all mean? Electrons are travelling through the
conductors The more electrons pass by every second, the more
brightness we see in the bulb. We call this CURRENT = rate of
charge past a point How can we tell how much current there is?
Slide 7
Series and Parallel Put 2 bulbs in a row connected to the same
# of batteries. How does the brightness change? What will happen
with 3 in a row? Why do you think this happens? Bulbs in a row are
called SERIES
Slide 8
Parallel Put two bulbs in PARALLEL (as shown on the board).
What happens to their brightness compared to before? What about the
total current? Can we tell for sure? How do we test this? The
splits in the wires before parallel bulbs are called JUNCTIONS
Slide 9
Total Current See section 3 Models of electric circuits!
Slide 10
Circuit Parts Battery Voltage Potential Difference Wire just a
connection, path of conductors Bulb Resistance and Brightness
(current) Other Resistors
Slide 11
Diagrams Circuit Diagrams: Battery Wire Bulb Capacitor Resistor
(other than a bulb) Diode/LED
Slide 12
More Stuff Fuses AC/DC Current - Drift velocity vs. velocity of
an electron
http://www.stmary.ws/highschool/physics/home/animations3/electricity/electrons_conductivity.html
Slide 13
meters Charge is said to flow THROUGH a circuit Current is said
to be THROUGH a bulb Voltage is said to be placed ACROSS a circuit
Voltage can be calculated ACROSS a battery Why? (hint: what are the
definitions of the two words) How do we measure current and
voltage?
Slide 14
Meters What are we measuring? Ammeter- # electrons passing by
per second Voltmeter potential difference between 2 points
Slide 15
Ohms Law George Simon Ohm 1789 1854 Taught math Most physicists
did not use math, just observed He combined observations and math
Ohms Law V = IR
Slide 16
Questions How much current is drawn by a lamp that has a
resistance of 60 when a voltage of 12 V is impressed across it?
What is the resistance of an electric frying pan that draws 12 A
when connected to a 120 V circuit?
Slide 17
Kirchhoffs First Rule Kirchhoffs First Rule: The total current
out of a node is equal to the total current into the node. (current
in = current out) i 1 + i 2 = i 3 + i 4 +i 5 The algebraic sum of
the currents at a node is zero. i 1 + i 2 i 3 i 4 i 5 = 0
Slide 18
Resistances Resistors in parallel add together like this: 1/R T
= 1/R1 + 1/R2 + 1/R3 + . Resistors in a row (series) add together R
T = R1 + R2 + R3 +
Slide 19
Rules for Circuit Analysis Redraw the circuit resistors in
series and parallel Simplify combine each set of series and
parallel Find Req for the entire circuit Find I total current
though the battery Use Kirchoffs Law to find other I values
