aim: how can we explain parallel circuits? do now: a series circuit has 3 resistors, 20 Ω, 40 Ω,...
TRANSCRIPT
Aim: How can we explain parallel circuits?
Do Now:
A series circuit has 3 resistors, 20 Ω, 40 Ω, and 60 Ω. What is the total resistance?
RT = R1 + R2 + R3
RT = 20 Ω + 40 Ω + 60 Ω
RT = 120 Ω
RT in series is always larger than the largest resistor!
Parallel Circuits
•A circuit with 2 or more current loops
Draw 2 resistors and a battery in a parallel circuit
Or…
Or…
Light Bulb Demo
If one goes out, the others remain lit
In a parallel circuit…
• Voltage is constant
• Total current is the sum of the currents through each resistor
And resistance…
Straw Demo
RT in parallel is always smaller than the smallest resistor!
R1 = 10Ω, R2 = 20Ω, R3 = 30Ω, in parallel with a VT = 100V
• Draw this circuit
• Calculate the current though each resistor
R1 = 10Ω R2 = 20Ω R3 = 30Ω
VT = 100V
V I R
1 100V 10 A 10Ω
2 100V 5 A 20Ω
3 100V 3.3 A 30Ω
T 100V 18.3 A 5.5 Ω
Draw a parallel circuit with a battery, 3 resistors, an ammeter reading the current through R1 and an ammeter reading the current through R3. R1 = 2Ω, R2 = 4Ω, R3 = 8Ω, and the ammeter for R3 reads 2.5 A.
R1 = 2ΩR2 = 4Ω
R3 = 8Ω
I3 = 2.5A
V I R
1 20V 10 A 2Ω
2 20V 5 A 4Ω
3 20V 2.5 A 8Ω
T 20V 17.5 A 1.1 Ω