Parallel circuits Current changes for each resistor Voltage

Parallel circuits Current changes for each resistor Voltage stays the same

Parallel circuits have the resistors stacked up together x x There is more than one path the current can follow – it is split at the junction

Parallel circuits have the resistors stacked up together x x Voltage stays the same, but current changes depending on the strength of the resistors

Parallel circuits have the resistors stacked up together x x If the resistors are the same, the current is divided equally in half

Parallel circuits have the resistors stacked up together x x If the resistors are different, the current is split proportionally

Parallel circuits have the resistors stacked up together x x Strong resistors have weak current, and weak resistors have strong current

The emf (Ԑ) at the power supply stays the same – it is the total power in the circuit x V x The current (I) will change across each resistor because each of them takes up some current

Kirchhoff’s First Law:

Kirchhoff’s Second Law:

How to solve a parallel circuit Step 1. Identify what you have, and what you need Step 2. Calculate the equivalent resistance Step 3. Find the voltage Step 4. Find the current for each resistor Step 5. Find the total current, and make sure it adds up

How do we do measurements if we have more than one resistor in parallel? Combine the resistors into the equivalent resistance (Req) as if it was one resistor

if we have resistors in series and in parallel (aka combination circuits)? There are no calculations needed! Use what you know about series and parallel circuits (current, voltage)

Find the missing values Ԑ = 12 V I 1 = 4 A I 2 = 3 A V 3 = 10 V V 2 = ? I 3 = ? R 2 R 1 R 3

Step 1. Identify which resistors are in series, and which are in parallel Ԑ = 12 V I 1 = 4 A I 2 = 3 A V 3 = 10 V V 2 = ? I 3 = ? R 2 R 1 R 3

Step 1. Identify which resistors are in series, and which are in parallel Ԑ = 12 V I 1 = 4 A I 2 = 3 A V 3 = 10 V V 2 = ? I 3 = ? R 2 R 1 R 3 Series: R 1 Parallel: R 2, R 3

Step 2. Identify which values should be the same for each resistor Ԑ = 12 V I 1 = 4 A I 2 = 3 A V 3 = 10 V V 2 = ? I 3 = ? R 2 R 1 R 3 Series: R 1 Same current Parallel: R 2, R 3 Same voltage

Step 3. Find the missing values Ԑ = 12 V I 1 = 4 A I 2 = 3 A V 3 = 10 V V 2 = 10 V I 3 = ? R 2 R 1 R 3 Since V 2 is in parallel with V 3, they have the same voltage V 3 = V 2 = 10 V

Step 3. Find the missing values Ԑ = 12 V I 1 = 4 A I 2 = 3 A V 3 = 10 V V 2 = 10 V I 3 = 1 A R 2 R 1 R 3 Since I 3 is in parallel with I 2, adding both values gives It = I 1 I 3 = I 1 – I 2 = 4 A – 3 A = 1 A

Why do we bother with series and parallel circuits? Who cares?

Series circuit Airfield lighting Christmas lights Series circuits are used when the lights all need to be on at the same time or they use the same current

Parallel circuit Car headlights Lamp Parallel circuits are used when the lights need to be turned on independently or they use the same voltage