VoltageCurrent

Resistance

But first I want to talk about water.

Does the water in bucket #1 have Gravitational Potential Energy?

NO, since the bucket is on the ground it has zero height. It is as low as it can go.

1

Does the water in bucket #2 have Gravitational Potential Energy?

Yes, since the bucket is above the ground it has height. And it would take "work" to move water from the pool to the bucket.

1

2

What about #3? It has even more GPE, since it is higher.

1

2

3

Each drop of bucket #3 has 10 Joules of energy.

1

2

3Each drop of bucket #2 has 5 Joules of energy.

Drops that fall from #3 would hit the ground faster and harder than from #2

Each drop of bucket #3 has 10 Joules of energy.

1

2

3Each drop of bucket #2 has 5 Joules of energy.

The pressure from #2 is 5 psi

The pressure from #3 is 10 psi

The pressure depends on the height of the bucket

5 psi 10 psi

Bucket #3 has more total energy that bucket #2

10 Joules per drop

2

3

5 Joules per drop

5 psi 10 psi

How many Joules per drop would be in #4 ?

4

10 psi

10 Joules per drop

What would the pressure be from #4 ?

10 Joules per drop

2

3

5 Joules per drop

5 psi 10 psi

How is #4 different than #3

4

10 psi

10 Joules per drop

It would have more total energy because it has more drops.

10 Joules per drop

3

10 psi

4

5 psi

5 Joules per drop

Now which as the most pressure?

The higher #3

Which bucket has the most potential energy?

About the SAME#3) 1000 with 10 = 10,000#4) 2000 with 5 = 10,000

Drops of water are like electrons.

Drops of water move through pipes.

Electrons move through wires.

Pressure pushes water through pipes

Volts push electrons through wires

Volts: The amount of the push force (pressure)

causing the charges to move.

Electrons experiencing high voltage have more push trying to make them move.

The water drops coming from the higher bucket were under greater pressure.

Volts can also be defined as the amount of potential energy each electron has.

Volts = Joules per Coulomb of electrons

A Coulomb is: 6 x 1018 electrons( a drop of electrons)

10 Volts = 10 Joules/C

1

5

10

5 Volts = 5 Joules/C

1 Volt = 1 Joule / C

10 Joules per drop

3

10 psi

4

5 psi

5 Joules per drop

2

5 Joules per drop

Since the drops in #2 and #4 all have 5 Joules.

The are all experiencing the same voltage force.5 psi

High voltageHigh pressure

1.5 volts 120 volts

Low voltageLow pressure

Volts: The amount of the push force (pressure)

causing the charges to move.Electromotive force, ( emf )

Volts: The amount potential energy Each

Coulomb of Charge will have

Volts: push on electrons causing them to

move and flow through conductors.

More volts = harder push =

faster flow of electrons

Moving electrons = current

Current: measured in Amperes (amps)

1 amp = 1 C per second (1 drop per second)

(rate of charge/second

A flow of 5 amps means:every second 5 Coulombs of charge go by.

12

12 psi

5

5 psi

5

5 psi

10

10 psi

2

2 psi

Water would flow from 12 to 5 with 7 volts of pressure.

IOW: every Coulomb of charge would loose 7 Joules of energy as it dropped.

20 drops per second

12

12 psi

5

5 psi

5

5 psi

10

10 psi

2

2 psi

Water would flow from 5 to 2 with 3 volts of pressure.

IOW: every Coulomb of charge would loose 3 Joules of energy as it dropped.

8 drops per second

12

12 psi

5

5 psi

5

5 psi

10

10 psi

2

2 psi

Water would flow from 12 to floor with 12 volts of pressure.

Every Coulomb of charge would loose 12 Joules of energy

35 drops per second

12

12 psi

5

5 psi

5

5 psi

10

10 psi

2

2 psi

Water would NOT flow from 5 to 5

In the absence of pressure water and electrons will not flow

12

12 psi

5

5 psi

5

5 psi

10

10 psi

2

2 psi

Notice that the greater the fall (difference in height) the greater the flow.

The greater the volt difference the greater the current of electrons.

35 drops/s

12 drops/s

12

12 psi

5

5 psi

5

5 psi

If it takes 5 seconds for 10 Coulombs to flow through the tube, what was the flow in amps?

amps = Coulombs per second

2 amps = 2 C/ second

There are a number of ways electrons can be pushed.

IOW: there are many sources of emf or voltage.

A charged object brought near a conductor will cause the electrons in the object to be pushed.

IOW: it will create a voltage (emf) on the electrons

A magnet moving past a conductor will cause the electrons in the object to be pushed.(create a voltage )

Friction, or the rubbing of different materials will cause a transfer of electrons

(create a voltage )

Some chemical reactions will result in the build up of electrons on one of the reactants.

(create a voltage )

Resistance( is futile )

12

12 psi

In this previous example we said that 2 drops per second would leave the bucket.

The current out of the bucket depends on how much pressure (height) of the bucket.

The current would also depend on the size of the hose.

This hose would allow a current of 18 amps (drops per second)

Conductors allow the flow of electrons (and water)

Insulators block the flow of electrons (and water)

Resistors allow flow of electrons, but they hold them back and slow them down.

12

12 psi

Both of these hoses are resistors.

They conduct electrons (water) but the electrons encounter resistance and are held back and slowed down.

The resistance of a hose carrying water would

depend on:

1. Material

Is the hose smooth or rough on the inside

1. Size of the hose

Smaller diameter hose has more resistance.

2. Length of wire

Longer hose has more resistance.

The resistance of a wire carrying charge would

depend on:

1. Material type

How easily the electrons get passed from atom to atom

2. Size of the hose

Smaller diameter wire has more resistance.

3. Length of wire

Longer wire has more resistance.

4. Temperature of the wire.

Many substance become more resitive the higher the temp.

Resistance is measure in Ohms. ( )

Current = Volts / Resistance

𝑰 =𝑽

𝑹Ohm’s Law

V = voltage difference Measured in V

I = current Measured in Amps

R = resistance Measured in Ω

Ohm’s Law

Current is directly proportional to the voltage difference.

Higher voltage, results in higher current.

Higher Resistance, results in lower current.

𝑰 =𝑽

𝑹𝑽 = 𝑰𝑹

High Pressure (volts)

High current

Low Pressure (volts)

Low current

High Resistance (ohms)

Low current

Low Resistance (ohms)

High current

12 v 3 amps

300 v 57 amps

12 v 3 amps

12 v 19 amps

20 gallons per second

20 gallons per second

Current is how much water passes per second.

Which pipe has the greater current?

20 gallons per second

20 gallons per second

Which pipe has the faster moving water?

20 gallons per second

20 gallons per second

Amount of water molecurles moving per second is not the same as the speed of the water molecules.

20 amps

20 amps

Which wire has the greater current?

20 amps

20 amps

Which wire has electrons moving faster?

The average speed of the electrons = Drift speed.

20 amps

Which wire has electrons moving faster?

The average speed of the electrons = Drift speed.

Drift speed of electrons are typically around 1 meter per hour.

However, most of you have heard that “Electricity moves at the speed of Light”

Electric impulses move at the speed of light.

So when you push one electron into the end of a wire, another pushes out the other side almost instantly.( similar to a Newton's Cradle )

When I tap on one end of the water column, water on the other end shoots out, almost immediately.

VIDEO: How fast is

Electricity?

VIDEO: What is an Amp?

VIDEO: What is a Volt

What is the voltage difference of a circuit

that has 0.75 amps of current flow

through a resistance of 10 Ω ?

V = 7.5 V

𝑽 = 𝑰𝑹

𝑽 = 𝟎. 𝟕𝟓 ∗ 𝟏𝟎

A fan is drawing 2 amps and has 4.5 ohms of resistance, what is the voltage of its power source.

V = 9 V

𝑽 = 𝑰𝑹

𝑽 = 𝟐 ∗ 𝟒. 𝟓

What is the current produced with a 9 V battery through a resistance of 100 ohms?

𝑰 = 𝟎. 𝟎𝟗 𝒂𝒎𝒑𝒔

𝑽 = 𝑰𝑹

𝟗 = 𝑰 ∗ 𝟏𝟎𝟎

An electric toothbrush operates on 120 V and has a current of 0.0125 amps. What is its resistance?

𝑹 = 9,600. Ω

𝑽 = 𝑰𝑹

𝟏𝟐𝟎 = 𝟎. 𝟎𝟏𝟐𝟓 ∗ Ω

Worksheet # 10