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# III. Creating an electromagnet

Wrap an insulated copper wire around a nail.
Connect the ends to a single 1.5 v battery.
It will become magnetized; try picking up staples!
Caution – the resistance is low so the current will be high.
Much of the current’s energy turns into waste heat.
After a few seconds it might burn one’s fingers.

# IV. Creating a generator

### A. Rotate a magnet through a coiled wire (less common)

Example “A dynamo is an energy-generating hub built into the front wheel of a bicycle that typically powers lights. Dynamos can also power USB ports and all manner of fun things, if you’re interested.”

### B. Rotate wire through a permanent magnet (more common)

PBS American Experience series: Inside the AC Generator

But how do we rotate any of these things to begin with?
Won’t happen by itself
We could study the generation of power, to learn how this happens.
Common sources of power to do this include:
Human powered: Check out the bicycle power dynamo, above!
Fossil fuels: Burning oil, coal, natural gas
Nuclear fission: urnanium nuclear reactors
Renewable energy: solar, wind, geothermal, tidal power, hydropower

## MCAS questions

Questions assume that you know the names of common electrical equipment!

Questions assume that you know what a circuit schematic looks like
Here we see a circuit:
A wire was broken, and reconnected with an ammeter inside the wire – so the ammeter feels the current flowing through it.
We also see a voltmeter being used. Nothing needs to be broken. We just put one lead on side of a component, and the other lead on the other side. The voltmeter then tells us the potential difference (voltage drop) across the component.

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### Which of the following forces allow a battery-powered motor to generate mechanical energy? (2014)

A. magnetic and static             B. electric and magnetic

C. static and gravitational       D. electric and gravitational

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### Which of the following statements describes an electric generator? (2013)

A.  A magnet is rotated through a coil of wire to produce an electric current.

B.  Electric potential in a rotating coil of wire creates a permanent magnet.

C.  An electrical current causes a coil of wire to rotate in a magnetic field.

D.  Forces from a permanent magnet allow a coil of wire to rotate.

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This next one is from 2010

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### Which of the following would cause the galvanometer needle to move?

A. wrapping additional wire around the tube

B. uncoiling the wire wrapped around the tube

C. moving a magnet back and forth inside the tube

D. moving an aluminum block up and down inside the tube

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## Electromagnet conceptual exercises

Questions & animations from Dynamic Science (Australia)  http://www.dynamicscience.com.au/tester/solutions1/electric/electromagexe.htm

A wire was spotted protruding from a wall. Both Jonathon and Stephen wanted to know if a current was flowing through the wire. They placed two magnetic compasses near the wire as shown in the animation on the right. Jonathon concluded that the wire carried a steady current. Stephen thought that someone was turning the switch off and on and did not agree with Jonathon. Who is right? Explain.

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Irene bought a new house and found that an unknown wire was coming up through a hole in the floor. She wanted to know if it had a current running through it. She placed two magnetic compasses around the wire and noticed the deflection of the needles.

Is there a current flowing through the wire? How can you tell?
If a current is flowing how is it changing? Explain.

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An electrician was working on a building site when he came upon an insulated wire. He was told that all the power to the site was turned off, but he wanted to make sure. He pulled out a magnetic compass and placed it near the wire as shown in the animation on the right. What can he conclude from his observations?

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A magnetic compass was brought close to two wires as shown on the left. What can you conclude from your observations?

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### Textbook/resources: Glencoe Physics

Chapter 24, Section 1, Section 2. Chapter 25 section 1

## Learning Standards

Massachusetts 2016 Science and Technology/Engineering (STE) Standards

7.MS-PS2-5. Use scientific evidence to argue that fields exist between objects with mass, between magnetic objects, and between electrically charged objects that exert force on each other even though the objects are not in contact.

7.MS-PS3-2. Develop a model to describe the relationship between the relative positions of objects interacting at a distance and their relative potential energy in the system. {Examples could include changing the direction/orientation of a magnet.}

HS-PS2-4. Use mathematical representations of Newton’s law of gravitation and Coulomb’s law to both qualitatively and quantitatively describe and predict the effects of gravitational and electrostatic forces between objects.

HS-PS2-5. Provide evidence that an electric current can produce a magnetic field and that a changing magnetic field can produce an electric current.

HS-PS3-2. Develop and use a model to illustrate that energy at the macroscopic scale can be accounted for as either motions of particles and objects or energy stored in fields [e.g. magnetic fields.]

HS-PS3-5. Develop and use a model of magnetic or electric fields to illustrate the forces and changes in energy between two magnetically or electrically charged objects changing relative position in a magnetic or electric field, respectively.