Lab # 8: Electricity and Magnetism

Background InformationElectromagnetsElectrical current (electrons) flowing through a wire produces a magnetic field, althoughthe field produced is weak. Coiling the wire increases the strength of the magnetic field.The strength of the magnetic field can be increased by the 3 C's:

1. having more Current flow through the wire 2. shaping the wire into a coil and increasing the number of Coils (turns) of wire 3. shaping the wire into a coil and inserting an iron CoreElectromagnets are used on cranes in scrap metal yards for lifting iron and steel, inspeakers, in microphones, in guitar pickups and in all electric motors.

The Motor EffectA force is produced when a current carrying wire (electromagnet) is placed in a magneticfield. The size of the force experienced can be increased by:

1. increasing the strength of the magnetic field 2. increasing the current in the wireIf the wire is parallel to the magnetic field it does not experience a force.

Fleming’s Left Hand Rule is used to determine the direction of the force experienced bythe wire.

Prelab questions:1. Which two of the devices mentioned above (at the end of the electromagnet section)

incorporate the Motor Effect? _____________________________________________

2. What do the concentric circles represent in the picture below?___________________

____________________________________________

3. Is the diagram below showing current going into, or coming out of a the page?_______________

4. Using the left hand rule, which direction will the magnetic field push the wire (Force)? a. upward c. rightward

b. downward d. leftward

Directions:Part 1: Observe magnetic field lines of permanent magnet

Place blank sheet of paper on top of magnet and trace the outline of the magnet. Markwhich end is North and which is South. Lightly sprinkle iron filings uniformly over thepaper and then give the paper some gentle taps to allow the filings to align with themagnetic field. Sketch below (Problems 5-6)

Diagram A

Repeat instructions from above, but this time place two magnets beneath the paper end-to-end with North and North are as close as possible (Problems 7-8)

Diagram B

9. In diagram A, the filings follow the pattern of what invisible lines? ______________________________________________________________________________________

10. What property of an atom causes it to be magnetic? __________________________________________________________________________________________________

11. What is the difference between a non-magnetic and magnetic metal? _____________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Part 2: Build Device to Observe Motor Effect

Using a plastic card, hot glue gun, twosmall ceramic disk magnets and ~20cmof 26 gauge copper wire, build thedevice shown in the photos below.Place the magnets so that the insidesurfaces are opposite and that themagnet closest to the wire ends has itsNorth pole facing into the gap. Placethe wire through the middle of the gapso that it can move freely.

FUNCTIONAL DEVICE CHECKOFF (Problems 12-16: worth 5 points)

Part 3: Observe Motor Effect

Attach alligator clips to the end of each wire. Touch the alligator clip attached to the leftend of the loop to the positive end of a 1.5V D battery. Touch the end of the otheralligator clip to the negative terminal of the battery and observe the wire. Next, reversethe direction of current flow by reversing the battery. Remember that electrons flowfrom the positive to the negative terminal of a battery.

17. What happened when current from the battery flowed through the wire? __________

________________________________________________________________________

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18. What is the name of this phenomenon? _____________________________________

19. What are two devices which operate on this principle? _________________________

20. What happened with you reversed the battery polarity? ________________________

21. Why? _______________________________________________________________

Part 4: Make wire coil and observe magnetic field lines

Make a coil of 5 windings of copper wire about 5cm in diameter. Cut a 5cm long slit in apiece of paper. Attach alligator clips to the ends of the coil and attach to battery.Holding paper horizontally, insert coil halfway through the slit. Lightly sprinkle ironfilings uniformly over the paper and then give the paper some gentle taps to allow thefilings to align with the magnetic field surround the coil passing through the paper.

Diagram C:Sketch the magneticfield lines revealedby the iron filings.(Problem 22-23)

24. What pattern do the iron filings form in diagram C? ___________________________

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25. How are these magnetic field lines different than diagram A? What is missing? ____

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26. What is the same between your sketch of diagram C above and the diagram fromquestion number 2 at the beginning of the lab? __________________________________

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