Science Buddies: "Ask an Expert"

I am helping my son do the Science Buddies "Does the Size of Wire in a Circuit Matter?" as a science project. The instructions indicate to connect to a 6V battery, an ohm meter, and various wires. We have a standard analog meter from radio shack, http://www.radioshack.com/product/index ... age=search.

In the ohm mode, the instructions for the meter say to never connect to a voltage source when measuring resistence. This is contradictory to the instructions in Science Buddies. When we do follow the instructions for the meter, each wire reads zero. I have a friend who works with electricity. He read the Science Buddies experiment and said that thre should not be any variation in resistance the suggested lengths of wires suggested.

Can someone please help me? Am I missing something in the instructions?

Thank you

rshort wrote:I am helping my son do the Science Buddies "Does the Size of Wire in a Circuit Matter?" as a science project. The instructions indicate to connect to a 6V battery, an ohm meter, and various wires. We have a standard analog meter from radio shack, http://www.radioshack.com/product/index ... age=search.

In the ohm mode, the instructions for the meter say to never connect to a voltage source when measuring resistence. This is contradictory to the instructions in Science Buddies. When we do follow the instructions for the meter, each wire reads zero. I have a friend who works with electricity. He read the Science Buddies experiment and said that thre should not be any variation in resistance the suggested lengths of wires suggested.

Can someone please help me? Am I missing something in the instructions?

Thank you

One of our experts has come to the same conclusion as your friend. He says-

Does the Size of a Wire in a Circuit Matter? - I've done some additional thinking on this one and looked the NEC AWG resistance tables for various copper wire formulations of 16 AWG to 1/0 and a 1960's ARRL (American Radio Relay League) handbook resistance tables for smaller wire sizes. With readily available low cost ohm meters, you need at least 1000 feet of wire between 1/0 and 10 AWG to measure resistance directly to one significant digit. At least 500 ft of 12 AWG to 18 AWG. These are expensive unless you can borrow them. It is only after you get 30 AWG to 40 AWG that you can measure 10 feet of it by simple methods.

He suggests another experiment is much better- while it has a higher difficulty rating, it should work.

https://www.sciencebuddies.org/mentorin ... ?from=Home

Louise

He read the Science Buddies experiment and said that there should not be any variation in resistance the suggested lengths of wires suggested.

I'd state it that there won't be 'any "measurable" variation in resistance in the suggested lengths of wires' using the recommended measurement techniques. There are in fact differences; however, measuring them is a significant challenge for most electrical engineers who have never tried it.

This experimental write-up is an excellent example of what happens somebody comes up with a nice simple idea and "dry labs" it. Obviously, the author never tried it!

As your friend who works in electricity if he as access to some long spools of wire and would be willing to help you measure their length and resistance. A 250 foot carton of 14-2G or 12-2G type NM has three conductors, white, black, and bare (or green) that can quickly be spliced in series at both ends to form a 750 foot length that can be measured.