Parallel CircuitsFriday, April 4, 2015

Unit 9: Electricity Friday, 4/3 Pick up a warm-up sheet of paper from the Physics bin and

use GUESS to solve the following problem:

A handheld radio is powered by two 1.5 V battery. When the radio is turned on there is 40 ohms of resistance. How much resistance is in the circuit?

Upcoming dates: Tuesday, 4/7 – open note quiz (DATE CHANGE) Tuesday, 4/7 – last day to turn in missing electricity assignments Thursday, 4/9 – Electricity test (grade will go on the 6SW) Friday, 4/10 – End of 5SW

Types of Electricity

Dynamic Static

Direct Current (DC)

Alternating Current (AC)

Series ComplexParallel

Unit Overview

Resistors can be connected in series; that is, the

current flows through them one after another.

Series Circuits

KirchhoffKirchhoff’’s Ruless Rules

Loop Rule: Loop Rule: The sum of the potential differences The sum of the potential differences (voltage) around any closed circuit loop is zero(voltage) around any closed circuit loop is zero..

Resistor CircuitsResistor CircuitsSeries

1. 1. total resistancetotal resistance is the sum of the is the sum of the separate resistorsseparate resistors

RRTT = R = R11 + R + R22 + R + R33 + ... + ...

2. 2. currentcurrent is the same through each resistor is the same through each resistor

IITT = I = I11 = I = I22 = I = I33 = ... = ...

3. 3. total potential differencetotal potential difference is the sum of each is the sum of each

VVTT = V = V11 + V + V22 + V + V33 + ... + ...

In other words, in a series circuit,In other words, in a series circuit,resistance and voltage add,resistance and voltage add,but current stays the same.but current stays the same.

Series Circuit Example

Practice

Unit OverviewTypes of Electricity

Dynamic Static

Direct Current (DC)

Alternating Current (AC)

Series ComplexParallel

Circuit – In SeriesOnly one path

Circuit – In ParallelMore than one path

DirectionsUsing the items in your box create a parallel circuit

with three branches. Place a light bulb in each branch.

When all three light bulbs have illuminated do the following:

Disconnect a light bulb from one branch of the circuit. Record your observations.

Disconnect two light bulbs from two branches. Record your observations.

What do you think?If a circuit has multiple branches will the

voltage, resistance, and current behave differently? Write your thoughts in your notes.

KirchhoffKirchhoff’’s Ruless Rules

Junction Rule: Junction Rule: the sum of all currents entering the the sum of all currents entering the junction must equal the sum of all currents leaving junction must equal the sum of all currents leaving

the junction.the junction.

Parallel 1.1. reciprocal of the total resistance reciprocal of the total resistance is is

the the sum of the reciprocals of the sum of the reciprocals of the

separate separate resistorsresistors

1/R1/RTT = 1/R = 1/R11 + 1/R + 1/R22 +1/R +1/R33 + ...+ ...2. 2. total currenttotal current is the sum of the currentis the sum of the current

through each resistorthrough each resistorIITT = I = I11 + I + I22 + I + I33 + ... + ...

3. 3. potential differencepotential difference is the same is the same across across each resistoreach resistorVVTT = V = V11 = V = V22 = V = V33 = ... = ...

In other words, in a parallel circuit, resistance adds as reciprocals,

voltage stays the same, and current splits.

In other words, in a parallel circuit, resistance adds as reciprocals,

voltage stays the same, and current splits.

Practice

Review