Current Electricity Chapter 22 the charges start to move

Current ElectricityCurrent ElectricityChapter 22Chapter 22

the charges start to movethe charges start to move

Electric CurrentElectric Current

• Imagine a river, how do you Imagine a river, how do you measure its current? Is it the measure its current? Is it the same as speed?same as speed?

• Electric Current = Rate at which a Electric Current = Rate at which a charge moves through a cross charge moves through a cross section. section.

• I = Q/t I = Q/t

= Coulombs/second= Coulombs/second

= Amperes = Amperes

• When you call someone in New When you call someone in New York, how do they hear you? How York, how do they hear you? How does the signal get there?does the signal get there?

• How fast do electrons travel? How fast do electrons travel?

• There would be quite a delay.There would be quite a delay.

• The actual speed is called The actual speed is called Drift Drift VelocityVelocity and is not the same as and is not the same as the speed of the signal.the speed of the signal.


Electric CurrentElectric CurrentWhat if you place the Anode and Cathode from a battery in salt water?

Which way does current flow?Which way does current flow?Current is defined as Current is defined as the flow rate of POSITIVE CHARGEthe flow rate of POSITIVE CHARGE

There are two basic types of currentThere are two basic types of current

•AC and DCAC and DC

•Alternating and Direct CurrentAlternating and Direct Current


e e e e e e

e e e e e e

In a wire 10,000 In a wire 10,000 electrons pass by electrons pass by every nanosecond. every nanosecond. What is the current in What is the current in the wire?the wire?


•Electrical Resistance = Ratio of Electrical Resistance = Ratio of potential difference to current within a potential difference to current within a material.material.

•Ohm’s Law Ohm’s Law

V = IRV = IR

volt = amp * ohmvolt = amp * ohm

•So, what does a resistor do?So, what does a resistor do?

It controls current by turning It controls current by turning electrical energy into other forms of electrical energy into other forms of energy.energy.

Electric ResistanceElectric Resistance

Determine the Determine the electrical resistance of electrical resistance of a toaster. It is plugged a toaster. It is plugged into 115 V wall outlet into 115 V wall outlet and draws a current of and draws a current of 8.0 A.8.0 A.

Electric ResistanceElectric Resistance

Electric PowerElectric Power

• Power = Rate of doing work = Watt Power = Rate of doing work = Watt (J/s)(J/s)

• P = J/C * C/sP = J/C * C/s

• P = Volt * Amp = V * I = Energy from P = Volt * Amp = V * I = Energy from the electric company is not measured the electric company is not measured in joules but instead is measured in in joules but instead is measured in kWh = kilowatt hourskWh = kilowatt hours

• Watt = Joules/sec so Joules = Watt Watt = Joules/sec so Joules = Watt secsec


A 40 W light bulb and a A 40 W light bulb and a 75 W light bulb operate 75 W light bulb operate from 120 V. from 120 V.

a)a)Which bulb has greater Which bulb has greater current?current?

b)b)Which bulb has greater Which bulb has greater resistance?resistance?


In one month, your family In one month, your family uses 600 kWh of electricity uses 600 kWh of electricity from the electric company. from the electric company. If electricity costs If electricity costs $0.20/kWh how much will $0.20/kWh how much will you pay?you pay?


If electricity costs If electricity costs $0.20/kWh, how much $0.20/kWh, how much money will it be if you money will it be if you leave a 60W light bulb leave a 60W light bulb on for a whole day?on for a whole day?

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Current Electricity Chapter 22 the charges start to move