Ch. 20 - ElectricityCh. 20 -

ElectricityIV. Electrical Circuits & PowerIV. Electrical Circuits & Power

(p.706-714)Ohms LawSeries circuitsParallel circuitsPower

Things you should already Things you should already know or be able to do…know or be able to do…

• Construct a simple electrical circuit using wires, batteries and light bulbs.

• Can you do this??? You need to do this to pass this weeks test on Electricity

Learning Target:Learning Target:

Describe the relationships between current, voltage, and resistance.

Current, Voltage & ResistanceCurrent, Voltage & Resistance Electricity & Water Analogy: Pressure in a hose

(V), rate the water flows through the hose (I) and the diameter of hose ( R) are all related.

If you change one, it affects the othersThe relationship is known asOhm’s Law…

Voltage = Current x Resistance

V = I x R

Ohm’s LawOhm’s Law

Visual: Relationship between V, I and Rhttp://phet.colorado.edu/sims/ohms-law/

ohms-law_en.html

Learning Target:Learning Target:

Use Ohm's Law to calculate current, voltage, and resistance using correct units.

Ohm’s LawOhm’s Law

E. Ohm’s LawE. Ohm’s Law

Ohm’s Law

V = I × RV: potential difference (V)

I: current (A)

R: resistance ()

• Voltage increases when current increases.• Voltage decreases when resistance increases.

E. Ohm’s LawE. Ohm’s LawA lightbulb with a resistance of 160 is

plugged into a 120-V outlet. What is the current flowing through the bulb?

GIVEN:

R = 160 V = 120 V

I = ?

WORK:

I = V ÷ R

I = (120 V) ÷ (160 )

I = 0.75 A

I

V

R

Practice:Practice:

There is a potential difference of 12 volts across a resistor with 0.50 amps of current in it. The resistance of the resistor is _________.

A. 0.5 ohms

B. 6 ohms

C. 12 ohms

D. 24 ohms

Practice:Practice:

If there is a current of 6 amps flowing through a 3 ohm resistor, what is the potential difference in the circuit?

A. 0.5 volts

B. 2 volts

C. 9 volts

D. 18 volts

Practice:Practice:

If a circuit has a potential difference of 120 volts and a resistance of 10 ohms, what is the current that flows through the circuit?

A. 0.08 amps

B. 12 amps

C. 120 amps

D. 1200 amps

Practice:Practice:A bunch of science students get together every

Friday night for a science party. Last Friday, they watched a couple of episodes of Bill Nye the Science Guy. They used a TV requiring 2.00 amps and a DVD player requiring 0.50 amps and they used 120V outlets.

What is the resistance of the TV? A. 12 ohmsB. 60 ohmsC. 240 ohmsD. 1200 ohms

NEED Ohm’s Law Worksheet

Complete today in class (We’ll review in 15 minutes)

Practice:Practice:

Ohms Volts Amps4 100 25

15 150 102 30 159 45 56 48 8

Learning TargetsLearning Targets

Describe the difference between a series and parallel circuit.

Contrast how voltage and current are applied to light bulbs in series vs. parallel circuits.

A. Circuit ComponentsA. Circuit Components

A - battery C - light bulb

B - switch D - resistor

What are electric circuits?Circuits typically contain a voltage source, a wire conductor, and one or more devices which use the electrical energy.

What is a series circuit?

A series circuit is one which provides a single pathway for the current to flow. If the circuit breaks, all devices using the circuit will fail.

What is a parallel circuit?A parallel circuit has multiple pathways for the current to flow. If the circuit is broken the current may pass through other pathways and other devices will continue to work.

What is the difference between an open circuit and a closed circuit?

A closed circuit is one in which the pathway of the electrical current is complete and unbroken.

An open circuit is one in which the pathway of the electrical current is broken. A switch is a device in the circuit in which the circuit can be closed (turned on) or open (turned off).

B. Series CircuitsB. Series Circuits Series Circuit

current travels in a single path

• one break stops the flow of current current is the same throughout circuit

• lights are equal brightness each device receives a fraction of the total

voltage

• get dimmer as lights are added

C. Parallel CircuitsC. Parallel Circuits Parallel Circuits

current travels in multiple paths

• one break doesn’t stop flow current varies in different branches

• takes path of least resistance

• “bigger” light would be dimmer each device receives the total voltage

• no change when lights are added

A. Electrical PowerA. Electrical Power

Electrical Power rate at which electrical energy is converted to another form of energy

P = I × VP: power (W)

I: current (A)

V: potential difference (V)

A. Electrical PowerA. Electrical Power A calculator has a 0.01-A current flowing through it.

It operates with a potential difference of 9 V. How much power does it use?

GIVEN:

I = 0.01 A

V = 9 V

P = ?

WORK:

P = I · V

P = (0.01 A) (9 V)

P = 0.09 W

I

P

V

D. Household CircuitsD. Household Circuits

Combination of parallel circuits too many devices can cause wires to

overheat

Safety Features: fuse - metal melts, breaking circuit circuit breaker - bimetallic strip bends

when hot, breaking circuit

AssignmentAssignment

Read pages 706 – 714Complete the Electrical Circuits and

Power Review HandoutDue Thursday 6/12