5F20.50 - Series and Parallel Light Bulbs

John Prineas 50 & 100 Watt Bulbs in Series
John Prineas - Three 50 Watt bulbs bottom bulb disconnected
John Prineas - Three 50 Watt bulbs bottom bulb connected
Code Number:
Demo Title:
Series and Parallel Light Bulbs
Series and Parallel Circuits
Area of Study:
Electricity and Magnetism
Demo Stand with Bulbs (4) and Conducting Rods (2), Variac, 0 to 150 VDC Power Supply, Circuit Board, 12 Volt Lights, Batteries or 0 to 20 VDC Power Supply, 12 Volt Battery, Iron "Rabbit Ears", and Light Bulbs with Magnetic Connectors.

Video Credit: Jonathan M. Sullivan-Wood

The circuit board demo is an easier and less lethal version of the older demo.

Place the two iron "rabbit ears" into the outer banana connections on the battery.  Connect the light bulbs with the magnetic connectors across the ears to show parallel bulb connections.  Series connections can also be made with this apparatus.

Connect a 12 volt car battery to the stand.  Turn on the circuit switch.  The light bulbs may be arranged as desired or removed and replaced with the metal conduction rods.  12 volt DC bulbs of 25 watts, 50 watts, and 100 watts are available for use with this demonstration.

John Prineas has two circuits he uses on the 12 volt antique pipe stand.  The first above is just a 50 watt and a 100 watt bulb in series with the battery to show the brightness difference in bulbs that have different resistances.  The second uses three 50 watt bulbs.  Two are in series with battery and will glow with the same brightness when switched on.  Connect the bottom bulb so that it is in parallel with one of the series bulbs and one bulb glows bright and the bulbs that are in parallel will glow dimly.  A voltmeter is also added to this demonstration so that you may measure the voltages at any point in these circuits.


NOTE: The original variation of this demonstration used 120 volts AC.  We have converted this to 12 VDC for obvious safety reasons.  Since the 12 VDC bulbs require larger currents for operation, the 12 volt car battery is the power supply of choice.  You will probably have to polish all the connections on the bulbs and the stand so that they make good connections during operation.

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Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.