Electric Currents Chapter 34 What is an electric

Electric Currents Chapter 34 What is an electric current? What makes current flow?

An Electric Current is simply electrons traveling through a conductor like currents in a river

Why does the water in a river flow? Gravity is pulling it down, but a general rule of thumb is that an object has a tendency to move towards positions of lower energy. DPE

Water will stop flowing when there is no PE difference This is also when the pressures are equal on both sides

Water will stop flowing when there is no PE difference In order to keep water flowing we would need to maintain a difference in height

The water would have to be continuously pumped to keep it flowing

An electrical current is made up of little charged particles (electrons). What tells you the Potential Energy of an electron. (Hint J/C) Electric Potential (Volts)

Electrons travel from high to low voltages 2. 0 1. 5 1. 0 VV 0. 5 0. 0 - + + As electrons flow the potential difference is reduced.

No current flow when there is no potential difference. 0 V

In order to keep current flowing we need an electron pump. e 1. 5 V A battery keeps current flowing by maintaining a voltage difference (until it “dies”)

Chemical reactions in a battery pump electrons around a loop electrons used up at the cathode electrons are produced when the zinc “corrodes” at the anode

How would you measure the flowrate of water? Volume gallon time minute

The rate at which electrons “flow” is measured in current Q I= t the amount of charge that flows through a wire (C) per time (s) Electrical Current: Amperes or Amps for short 1 ampere = 1 Coulomb 1 second

What does as 15 amp circuit mean

One light bulb draws 1/3 amp Another draws 2/3 amp. How many more electrons pass through the second as compared to the first in one second?

The greater the potential difference (pressure) the faster the flow of water.

The bigger the electric potential difference, the faster the flow of electrons. As Voltage Current Voltage can be thought of as electrical pressure

How does the size of the hole affect flowrate? A small hole provides more RESISTANCE to water flow.

Electrical RESISTANCE of something (like a wire) is how much it resists electrons flowing through it. It is measure in OHMS W

The Electrical Resistance of an object depends on 4 things 1. ) THE MATERIAL Copper wire Glass rod Which will have the higher resistance?

The Electrical Resistance of an object depends on 4 things 2. ) The Length Short Long Which will have the higher resistance?

The Electrical Resistance of an object depends on 4 things 3. ) The thickness THICK THIN Which will have the higher resistance?

The Electrical Resistance of an object depends on 4 things 4. ) The Temperature The hotter an object the more it resists current. When some materials are cooled WAY DOWN, they actually lose all resistance and become SUPERCONDUCTORS

How would the resistance be affected if the wire was stretched out.

As Resistance is measure in Current Ohms W

Tube resistor valve switch pump + battery

pressure drop across Tube voltage drop across resistor valve switch - water flow pump e- flow + battery

Ohm’s Law V I= R Current (amps) Electrical Potential (Volts) Resistance (Ohms)

Ohm’s Law V I= R As Voltage Current As Resistance Current

A 9 -volt battery is place on your wet tongue which has a resistance of about 3000 ohms. How many amps run through your tongue?

Amperage Chart . 001 A. 005 A. 015 A. 100 A mild shock hurts loss of muscle control probable death

If you touch a 120 V circuit WET skin has a resistance of about 3, 000 W high current Dry skin has a resistance of about 500, 000 W low current

Why is the bird safely perched on a power line

A technician installs a bird diverter to keep condors away from points which may be grounded.

What resistance would you want, in order to flow 15 Amps through a 120 V circuit?

How much current flows across a light bulb with a resistance of 25 Ohms connected to a 12 V batter?

Voltage from a 12 V battery (Direct Current or DC) Current T

AC or alternating current Current 0 Time The US use AC current at 60 Hz, what does that mean

What happens to the current that flow through the wire? Current 0 Time At times the current is moving: left or right or not at all

Are there any electrons in a copper wire which is not connected to a battery? e- In a neutral wire, an electron moves randomly but doesn’t really go anywhere

Path of an electron in an electric field - + drift speed

An electron has a total speed of about 1, 500, 000 m/s but usually has a drift speed of about. 0001 m/s Path of an electron in an electric field - + drift speed

With a drift speed of about. 0001 m/s Why does it not take several minutes for the lights to turn on, when you hit the switch? The wires are already full of electrons, when one enters one exits.

The electron bumps into atoms in its path + - This slows its drift speed, & is also why a wire gets hot when current passes through it.

The hotter the wire, the faster the random motion of the electron is. The more frequently bumps into an atom, and loses drift speed. (the greater the resistance) Temp W

Electron motion applet Path of an electron in an electric field - + Which way would field lines point?

The electric company does not sell electrons all they do is jiggle the electrons in your wires which requires ENERGY When you get electric shock, its your own electrons that are shocking you!

In order for current to flow, a circuit must be made Which circuits will have current?

Which light bulb(s) will light?

Which light bulb(s) will light?

BOOK Problems Page 546 2 -16, 26 - 32

Energy No resistance = No energy loss 9 V 9 V battery 0 V

Electric POWER Energy Power = time

If you were looking for the power of a waterfall, what 2 factors would determine it

the height of the falls, the change in PE of the water the flowrate of the water

For electric power, it is very similar the flowrate of electrons the change in PE of the electron P =I V Power J/s (Watt, W) Current C/s Voltage J/C

I P Energy 9 V battery

I P Energy 9 V battery The voltage is the same so each electron gives the same amount of energy, but more electrons pass through each second

V P Energy 9 V battery 0 V

V P Energy 120 V battery Even if the current is the same, the Power increases because each electron drops off more energy!

What power is used by a 2 amp toaster on a 120 V circuit?

A 60 watt bulb is made to flow. 50 A, what voltage is it intended to be plugged into?

If you were to connect 2 resistors together (or anything else) there are two ways to do it.

parallel series

Which will be harder to push water through Twice as hard

When resistor are positioned in series the total resistance just adds up Total or EQUIVALENT resistance 4 W 4 W 4 W 8 W 8 W 4 W 8 W 12 W

What is the total current running through each circuit 4 W 2. 0 A 8 V 4 W 1. 0 A 4 W 8 V

Because the current can only go in 1 path, the current through both resistors is the same 1. 0 A 4 W 1. 0 A 8 V 4 W 1. 0 A

Same flow rate everywhere

Pressure drops after resistance 50 Pa 100 Pa

Voltage drops after each resistor 8 V 0 V 4 W 4 W 1. 0 A 8 V

Voltage drop is given by Ohms Law V = IR 4 W 4 W 4 V drop 1. 0 A 8 V

nd resistor? What the voltage drop across the resistor? Whatisisisthe thevoltagedrop between across thethe resistors? 2 first Energy 4 W Energy 8 W 24 V

A lamp with a resistance of 360 W and one that is 144 W are connected in series to a 120 V circuit. Which burns brighter?

3 light bulbs each with a resistance of 2 W, are connected to a 9 V battery. What is the current and voltage at each point along the circuit Which bulb is the brightest? 9 V

What happens if one bulb burns out? 9 V

What happens if one bulb burns out? 9 V

What happens to the brightness of a bulb, if another is connected in series. ? 9 V 9 V

The bulbs are dimmer, the same voltage with more resistance means… less current 9 V 9 V

Which will be easier to pump water through? There are Twice the paths open to the water The resistance is only 1/2 , so twice as much water will flow

Resistors can also be added in Parallel Which circuit has the higher Resistance to current flow? 4 W 4 W 4 W

Equivalent Resistance 4 W 4 W 2 W 4 W 4/3 W

4 W 4 W 4 W As more resistors are added in PARALLEL, the equivalent resistance DROPS

R 1 R 2 R 3 1 1 = REQ R 1 REQ = + 1 R 2 + 1 R 3 + etc…

Equivalent Resistance 4 W 4 W 1 1 1 = + 2 W 4 W 4 W 1 1 = + + 4/3 W 4 W 4 W

What is the equivalent resistance of a 10 ohm and 20 ohm resistor in series and parallel?

Page 559 3, 4, 5, 6, 9, 10, 11 due next class

What is the equivalent resistance 4 W REQ=2. 7 W 8 W What is the total current out of the battery? I=3. 3 A 9 V Is the current the same through each resistor?

Which resistor has the greatest voltage drop? 4 W 9 V 8 W 9 V 0 V

Which resistor will have the greatest current? 4 W 8 W 9 V

Will the flow rate be the same through both tubes? Both tubes are fed the same pressure

Which resistor will consume the greatest power? 4 W 8 W 9 V

What would happen the Voltage, Current, and Resistance if another resistor was added in parallel? 24 W 4 W 8 W 9 V

How does the brightness change if another bulb is added in series? What changed? ½ Resistance Twice current battery drains twice as fast 9 V 9 V

What if one burns out? 9 V

What if one burns out? 9 V

A light bulb with a thick filament and one with a thin filament are connected in parallel to a battery. Which will burn brighter? 9 V

to other circuit breakers Hot From Power company Circuit Breaker or fuse (15 A) 8 Amp Microwave 7 A Fridge unused outlet

to other circuit breakers Hot From Power company Circuit Breaker or fuse (15 A) 8 Amp Microwave 7 Amp Fridge 1 Amp light

to other circuit breakers Hot From Power company Circuit Breaker or fuse (15 A) 8 Amp Microwave 7 Amp Fridge 1 Amp light

What is the equivalent resistance of the circuit below 4 W 2 W 6 W

What is the equivalent resistance of the circuit below 4 W 4 W 4 W How much current would flow from a 100 V batttery?

Book problems page 560: 16, 17, 28, 29

What is the current out of the battery? Which of these resistors will have more current? 80 W 20 W 12 V I 1 40 W

4 W 20 W 15 W 40 W 10 W 4 W 24 V

What is the equivalent resistance of the circuit below 4 W 6 W 20 W 10 W 2 W 40 W

Book problems: p 561 29 -32

Energy 9 V battery

nd resistor? What the voltage drop across the resistor? Whatisisisthe thevoltagedrop between across thethe resistors? 2 first Energy 4 W Energy 8 W 24 V

8 W 4 W 9 V Energy

Energy 8 W Energy 4 W 9 V