Electromagnetic Induction Created for CVCA Physics By Dick Heckathorn 25 April 2K + 5

Table of Contents 1 19.1 Electromagnetic Age 8 F on wire in B 11 Insert magnet into a coil 19 I transmitted by iron core 25 19.4 Lenz’s Law 31 Examples of Induced direction 37 19.5 Electrical Generators 46 19.6 The Transformer 55 Energy Transmission 61 Demonstrations

What physics principles does this picture illustrate?

Purpose for Chapter 19 To investigate how one can generate electrical energy (electricity) 2. Techniques for distribution

Only known source of continuous electric potential 19.1 Electromagnetic Age 738 Voltaic Cell Only known source of continuous electric potential

Can a magnetic field cause electrons to move? 19.2 Faraday’s Discovery 738 Question? Can a magnetic field cause electrons to move?

Large magnet – wire – Galvanometer Demonstration #1 Move a wire through the jaws of a horseshoe magnet. Results? Large magnet – wire – Galvanometer

N FMag FMech IInd B that is equal in magnitude gives rise to a magnetic force A Mechanical Force is but in the opposite direction. to the mechanical force This induced current in a B field An induced current is produced. exerted on a wire in a B field. N FMech FMag IInd B

when the conductor was moving through the magnetic field. Demonstration #1 Electrons only flowed when the conductor was moving through the magnetic field. They were moving in a direction opposite to the induced current as the induced current was the movement of positive charges.

Bar magnet – coil – wire – Galvanometer Demonstration #2 Plunge a bar magnet into and out of the core of a coil. Bar magnet – coil – wire – Galvanometer

Demonstration #2 FMech I B Due to mechanical force to right Direction of blue arrows Magnet’s field has direction of: Or coil moves to right Magnet plunge into the coil. B field of magnet at bottom of coil is in what direction? Thus induced current is in direction….

Demonstration #2 FMech I B Magnet’s field has direction of: Due to mechanical force to left Magnet pulled out of the coil. B field of magnet at bottom of coil is what direction? Direction of blue arrows Or coil moves to left Thus induced current is in direction….

Factors affecting magnitude of induced current Number of turns of wire in the coil Strength of magnetic field of the magnet 3. Rate at which magnetic field changes relative to wire (relative speed)

Direction of the Magnetic Field relative to right side of coil is: Direction of the mechanical force on wire is: B I FM Direction of the Induced Current is:

Direction of the Magnetic Field relative to right side of coil is: Direction of the mechanical force on wire is: B I FM Direction of the Induced Current is:

B Direction of the Magnetic Field relative to right side of coil is: Direction of the mechanical force on wire is: none B Direction of the Induced Current is: there is none

the bar magnet is moving Conclusion Charges flow only when the bar magnet is moving into or out of the coil or when the coil moves relative to the magnet.

What happens to the meter? The two wires are not connected. Demonstration #3 What happens to the meter? Close the switch. Anything surprising? The two wires are not connected. Green or large power source – iron ring or my coils - wire – Galvanometer

What happens to the meter? Demonstration #3 Open the switch. What happens to the meter? Green or large power source – iron ring or my coils - wire – Galvanometer

Closing the Switch I ΔB ΔB Iind Close Switch B changes from zero to maximum throughout the iron ring. Current changes from zero to max Induced current in secondary will flow to set up ΔB opposite ΔB Results ?

Opening the Switch I ΔB ΔB Iind Open Switch B changes from maximum to zero throughout the iron ring. Current changes from max to zero Induced current in secondary will flow to set up ΔB opposite ΔB Results ?

There is an induced current Conclusion There is an induced current only when the magnetic field is changing in the iron ring.

19.3 Magnitude of Induced Electric Potential 738 Ohm’s Law Says:

19.4 Direction of Induced Current: Lenz’s Law 741 Know so far? S-Pole enters coil Current in one direction S-Pole removed from coil Current in opposite direction Know so far? S-Pole enters coil Induced current is in a direction opposite that when N-Pole was involved

inducing field of the magnet. Lenz Reasoned The induced current sets up an induced magnet field. This induced field interacts with inducing field of the magnet.

How do they interact? Either one or the other.

an induced magnetic field in coil The current would produce Lets assume S an induced magnetic field in coil R-hand rule says right end is: The current would produce S of bar magnet pulling them together. attract the N-Pole S-pole would Lenz reasoned: Impossible Why?

Lets look at other option an induced magnetic field in coil R-hand rule says right end is: The current would produce N Must do work to bring them together N-pole coil opposes N-pole magnet

flows in such a direction Conclusion An induced current flows in such a direction that the created induced field opposes the action of the inducing field.

What is direction of Iinduced? Lower end of coil must be: N Why? Coil must oppose removal of S-pole N R-hand rules says current flows across front of the coil. to left

What is the pole of magnet? Left end of coil must be: S Why? Right hand grasping coil correctly. Right pole of bar magnet must oppose South pole of coil therefore it must be: S

Polarity of Coil? Direction I ? Top of coil must be: N Why? Must oppose N-pole of magnet. N Current in coil must be (in wire near us): in direction:

Polarity of Coil? Direction I ? Bottom of coil must be: S Why? Must oppose S-pole of magnet. S Current in coil must be (in wire near us): in direction:

Polarity of Coil? Direction I ? R-end of coil must be: N Why? Must oppose S-pole of magnet. Current in coil must be in direction (in wire near us)

Polarity of Coil? Direction I ? S R-end of coil must be: S Why? Must oppose N-pole of magnet. Current in coil must be in direction (in wire near us)

19.5 Electrical Generators: AC and DC 745 Ready to produce a device capable of producing a continuous electric current and electric potential difference by electromagnetic induction

AC Generator B I F Look at segment X-W Force in direction? Induced current in direction? B in direction?

AC Generator B F Induced current in direction? Force in direction? Look at segment X-W ½ turn later B F Induced current in direction? Force in direction? B in direction?

AC Generator Summary I I

AC Current vs Time

DC Generator B I F Force in direction? Induced current in direction? Look at segment X-W B I F Force in direction? Induced current in direction? B in direction?

DC Generator B F I Force in direction? B in direction? Look at segment X-W ½ turn later B F I Force in direction? B in direction? Induced current in direction?

DC Generator - Summary I I

Maximizing Output Increase # turns on coil Winding coil on soft iron core Increase speed of rotation Increase strength of B-field

electrical generating 19.6 The Transformer All large scale electrical generating systems generate electricity using AC generators.

electric potential difference (V) The Transformer changes the electric potential difference (V) by varying number of windings of two different coils around a common soft iron core.

Green Power Source – Dissectible transformer – 2 multimeters Demonstration Repeat the potential difference and current measurements as done with coil within a coil. Investigate the construction of a dissectible transformer. Green Power Source – Dissectible transformer – 2 multimeters

Conclusion If power source is connected to the coil with the smaller number of turns, the output potential difference is greater than the input potential difference.

Conclusion If power source is connected to the coil with greater number of turns, the output potential difference is less than the input potential difference.

Conclusion If power source is connected to the coil with the smaller number of turns, the output current is less than the input current.

Conclusion If power source is connected to the coil with greater number of turns, the output current is greater than the input current.

Question How does the output power compare to the input power? Did Poutput = Pinput ? If so, there is a Conservation of Energy as the potential difference is changed.

Designing Transformers Copper coils – have low R to reduce power loss Core – High Permeability to reduce energy to ΔB in core Core’s Shape to maximize induction

Energy Transmission 12,000 V 240,000 V 2400 V 240 V The voltage must then be reduced to a value that is acceptable for home usage. The voltage is increased to reduce the energy lost as it is transferred through the wires over a long distance.

It is being transmitted at a rate The wire has a total resistance Transmission of Power Electrical energy is being transmitted on a wire of 1.2 cm diameter for a distance of 100 km. It is being transmitted at a rate of 550 watts (J/s). The wire has a total resistance of 16 ohms.

Transmission of Power If the potential across the two ends of the wire is 110 volts, what is the current? P = 550 W R = 16 Ω I = ? %Ploss ?

Transmission of Power P = 550 W R = 16 Ω I = ? %Ploss ? If the potential across the two ends of the wire = 110,000 volts, what is the current? P = 550 W R = 16 Ω I = ? %Ploss ?

Analyzing Converter Units Cell Phone Converter Analyzing Converter Units Input: 120 V-AC, 60-Hz, 8-W Output: 12 V-DC, 300-mW 1. Convert 120-V AC to 12-V AC 2. Ratio of turns is: 10 to 1 3. Convert 12-V AC to 12-V DC 4. Current relationships: In: 0.066 Amp Out: 0.025 Amp

Analyzing Innverter Unit Cell Phone Converter Analyzing Innverter Unit Input: 12 V-DC, ________W Output: 120 V-AC, 350-W 1. Convert 12-V DC to 12-V AC 2. Convert 12-V AC to 12-V DC 3. Ratio of turns is: 1 to 10 4. Current relationships: In: ___ Amp Out: ___ Amp

Demo - Coil 1. Used as Magnetizer 2. Two Rings – Adjust Height Induced Voltage Various Size Coils Bulb connected to coils Radio Transmission

Demo - Coil 7. Magnetic Braking 8. Dropping Magnet 9. Dropping Copper Tube 10. Ball Magnet

That’s all folks!