2006 Physics Assessment Task

7/28/2019 2006 Physics Assessment Task

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AC Generator

Aim:Research, design and build an electric AC generator. Control

and record the effects of changing two variables (varying thespace between the magnets and the armature, the velocity of

relative motion between the coil and the magnets).

Hypothesis: As we spin the coil relative to the magnets, the coils should

created an electric current that lights up our light bulb or

makes movement on the galvanometer.

The more coils we add, the greater the current produced when

in action.

The closer the magnets relative to the armature, the greater

the magnetic field on the armature and the greater the current

produced when in action.

The faster the velocity of relative motion between the coil

and the magnets, the greater the current produced.

Equipment:

2 Magnets (to produce a magnetic field in the coils)

Insulated copper wire (for the current to flow through)

Wood block(for the base)

Metal axel (for the armature to spin on)

Wood core (cylinder shape to act as the armature) 2 thin metal rectangular pieces (act as the brushes)

2 metal slip rings (to connect to the brushes)

Light Bulb (test if its producing current)

Tape and glue (stick stuff together)

2 small wood pieces (to support the axel at either end)

Electric hand drill (spin the generator)

Galvanometer(test the current)


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Method:

1. Construct all the parts together as in the diagram below.

2. Make a hole in the middle of the cylinder shape wood

piece and put the axel threw that hole (the wood pieceshould be near the end of the axel as seen in the diagram

below). Glue the ends so it doesnt move (see diagram).

3. Wrap 50 times around the wooded piece (armature) the

insulated copper wire and hold it in place with the tape or

glue (see diagram).

4. Glue the two metal slip rings to the axel. Connect one end

of the copper wire to one of the slip rings and the other end

to the other slip ring (see diagram)5. Make a hole in both the small pieces of wood to support

the axel at either end. Glue the pieces to the big block base

wood (see diagram).

6. Get the two thing metal pieces (brushes) and bend the tips

of one end for each brush. Glue each one down to the base

under a slip ring each so that they just touch (see diagram).

7. Connect one a wire from the bottom of a brush to the

positive hole of the light bulb and another wire from the

other brush to the negative hole of the light bulb (see

diagram).

8. Glue down the light bulb to the base (see diagram).

9. Position the two magnets on opposite sides of the armature

(3 cm away) so that a north pole faces a south pole (see

diagram).

10. Now you are ready to test it. Connect wires from the

2 brushes to a galvanometer. Spin from any side with an

electric hand drill. Record the current reading .

11. Now move the side magnets 5 cms away from their

original position relative to the armature and test it. Record

the current reading. Then move them 2 cms towards the

armature from their original position and test it. Record the

current reading.

12. Now for the other variable, turn the hand drill to a

faster velocity and record the current reading. Then turn


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the hand drill to a slower velocity from the original

velocity and record the current reading.

Results:

Distance of Magnets

from Armature (cm)Current reading on

Galvanometer (A)

3 (default)

8 (further)

1 (closer)

Velocity of the

Hand Drill

Current reading on

Galvanometer (A)


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Medium (default)

Faster

Slower

Risk Assessments Procedure: Be careful not to spin the axel to fast, it could cause a short

circuit or destroy the whole project. Keep the hand drill on

a safe speed .

Resources:

Jacaranda HSC Physics

Spotlight HSC Physics

http://www.phys.unsw.edu.au/~jw/HSCmotors.html

http://www.amasci.com/amateur/coilgen.html

Testing and Modifications:

The way I placed the magnets failed to get the generator

producing current so I had to get more magnets and place

them around the whole armature.

A week before the due date, I borrowed a galvanometer

from school to test my generator at home.

Results:

milli Volts (mV)

Speed Trail 1 Trail 2 Trail 3 Trail 4 Average

Slow 10 12 13 11 11.5

Medium 15 20 18 20 18.25
http://www.phys.unsw.edu.au/~jw/HSCmotors.htmlhttp://www.amasci.com/amateur/coilgen.htmlhttp://www.phys.unsw.edu.au/~jw/HSCmotors.htmlhttp://www.amasci.com/amateur/coilgen.html


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Fast 31 34 35 33 33.25

Conclusion:

The hypothesis stated: As we spin the coil relative to the magnets, the coils

should created an electric current that lights up our light

bulb or makes movement on the galvanometer.

The faster the velocity of relative motion between the coil

and the magnets, the greater the current produced.

As we spined the axle, spinning the coil on the armature relative

to the magnets, the coils created an electric current that gave

readings on the galvanometer. From our results we can concludethat the faster the velocity of relative motion between the coil

and the magnets, the greater the current produced. Therefore our

results support the hypothesis stated earlier and the hypothesis

was true.

My expected results:


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As we spin the coil relative to the magnets, the coils should created an electric

current that lights up our light bulb or makes movement on the galvanometer.

The faster the velocity of relative motion between the coil and the magnets, the

greater the current produced.

Researched results:

My researched results were very similar to my expected results, only they were more

accurate then mine since the way I tested my variables werent that precise. I found

out that the more rotations per minute the higher the voltage, therefore the faster the

velocity of relative motion between the coil and the magnets, the greater the current

producedas stated in my expected results.

Also from the formula

Torque = nBIAcosx

Where:

n = number of coils

B = strength of the magnetic field

I = amount of current

A = the area of the coil

we can clearly see how if we increased the torque, meaning the faster the velocity

of relative motion between the coil and the magnets, then the current (I) show also go

up. Since we only changed the speed, therefore we can say (n), (B) and (A) were

constant. Therefore the torque is proportional to the current and as the torque

increases so should the current.

References:

Author : Ken J Williams and Janet PembertonPublisher : Science PressPublished : 2002Book : Spotlight Physics HSC

Author : Walter FendtPublished : April 27, 2006Website http://www.wvic.com/how-gen-works.htm

If given more time and resources I would of:

Got stronger magnets since the greater the magnetic field the greater the

current. It would have made it easier since the generator needed a strong

magnetic field or a relatively fast torque; therefore it was hard to test it with

small speeds.

Got a smoother material for the axle since there was too much friction and it

made the whole generator very inefficient. Thus making it harder to produce a

current.

More suitable way of measuring the speeds since the hand drill wasnt very

accurate in determining the speed, I couldnt speed a constant for each speedlimit for each trails thus it couldnt be accurate.
http://community.boredofstudies.org/members/smokedsalmon/http://community.boredofstudies.org/members/smokedsalmon/http://www.wvic.com/how-gen-works.htmhttp://community.boredofstudies.org/members/smokedsalmon/http://www.wvic.com/how-gen-works.htm


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Edison VS Westinghouse

In the late nineteenth century Edison chose generating and supplying directcurrent (DC).

In the same period of time as Edison with DC, Westinghouse promoted the use

of alternating current (AC)

Edison had the initial advantage that the technology for generating DC was

well established and DC worked well over short distances, therefore leading to

huge and expensive energy losses over distances of more than 1 or 2

kilometres.

This required many power stations throughout the city and an unattractive

large number of wires.

AC could be transmitted over greater distances than DC, with smaller energy

losses and power stations could be fewer and conductors lighter.

Edison owned hundreds of DC power stations and all of his electrical

inventions to that time ran on DC. In 1892 he attempted to prove that AC was

very dangerous by electrocuting animals and convincing authorities to use AC

for the first electric chair.

The economic advantages of AC, such as the smaller energy losses and the

fewer power stations further apart, along with the unattractive web of wires

required with DC, supported Westinghouses solution over Edisons DC.

AC also got a boost in popularity with Teslas invention of the induction

motor which could operate only on AC.

Edison tried to have AC banned, though at the end he failed and AC becamethe dominant form in which electricity is generated world-wide.

AC vs. DC

AC Generators:

Advantages Disadvantages

easily transformed permitting

transmission over long distances

with less energy loss

requires less maintenance and is

more reliable than a DC

generator

the roles of the rotor and the

stator can be reversed for the

output current

more deadly than DC

has losses through electromagnetic

radiation or magnetic induction.


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brushes do not wear as fast as in

a DC generator

no possibility of creating an

electrical short circuit between

segments in an alternator

because the slip rings are alreadycontinuous

most commercial generators are

AC generators

better suited to high current

demands

DC Generators:

Advantages Disadvantages

output can be made smoother by

the arranging many coils in a

regular pattern around the

armature

use with equipment that needs a

steady voltage rather than

varying voltage (AC)

doesnt cause losses through

electromagnetic radiation or

magnetic induction.

not good for transmission over long

distances without great energy losses

more complicated to make and

maintain

limited usefulness of DC generators

to relatively low current applications

large currents through the

commutator-brush connection

increases the likelihood of electric

arcs forming as the brush breaks

contact with each bar in turn

References:

Author : Ken J Williams and Janet PembertonPublisher : Science Press

Published : 2002

Book: Spotlight Physics HSC

Author: SmokedSalmon

Published: 29 Oct 2003, 5:01 AM

Website: http://community.boredofstudies.org/264/motors-generators/16970/westinghouse-vs-edison.html
http://community.boredofstudies.org/members/smokedsalmon/http://community.boredofstudies.org/members/smokedsalmon/


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By: Mohamad Kobeissi

2006 Physics Assessment Task

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