Re: What is the effects of magnets on photographic film and computer diskettes?

Hi Catherine,

Let me preface this by saying that I turned to my colleague, Steve Sklar, who's an audio/video specialist with Zentropy, for help in answering the photographic film aspect of your question. In addition, I also consulted the MadSci archives for the chemistry involved in developing photographs.

The effects of magnetic fields on computer diskettes are pretty well known. Computer disks store information by encoding it magnetically on the disk itself. Thus, if a magnetic field is strong enough, it can lead to data degradation, all the way up to complete data corruption if the magnetic field is really strong. A possible experiment for your student might be to expose disks containing known files (maybe a few text files) to magnets of increasing strength and noting the amount of data loss with variation of the magnetic field.

For photographic film, the situation is drastically different. Photographic positives are pretty neutral to almost everything but I think your question was directed more towards the effects on photographic negatives. Basically, a photograph works by having certain areas of the film react to light and this photsensitivity is governed by the substance that coats these films (usually, some kind of silver salt, like AgBr). Since this is mainly a chemical reaction, magnetic fields don't affect it much... however, ionizing radiation (e.g., X-rays) can affect the film (the amount of radiation required for this depends on the film's ASA rating... the higher the ASA rating, the more photosensitive it is). If you're interested in the chemistry of developing films, I encourage you to check this previous answer from the archives. However, I definitely don't recommend bringing an X-Ray machine into the classroom to test film degradation with increasing X-Ray intensities!

Well, I hope this helped... if you need any further information at all (or if I didn't explain something well), please don't hesitate to drop me a line at science@zentropy.com and I'd be more than happy to discuss this further.

Best regards,

Rick.