# Why is it that lower frequency EM waves are aloud to pass through objects, but high

1. Nov 8, 2012

### jaydnul

But high frequency are absorbed, like gamma rays. I would think it would be the opposite. So whats the physical reason?

2. Nov 9, 2012

### Simon Bridge

Re: Why is it that lower frequency EM waves are aloud to pass through objects, but hi

I believe you'll find that gamma rays have higher penetration in, say, steel, than infra-red rays.
I can stop a lot of visible light with a black sheet of paper - but this has almost no effect on high energy gammas.

Where did you get this idea from?

3. Nov 9, 2012

### andrien

Re: Why is it that lower frequency EM waves are aloud to pass through objects, but hi

This does not seem right even if one invokes the concept of plasma frequency.Metals having plasma frequency higher than frequency of light will reflect it otherwise transmit.May be you can see feynman lectures vol. 2 ,last 1/4 part for it.

4. Nov 9, 2012

### superdave

Re: Why is it that lower frequency EM waves are aloud to pass through objects, but hi

Radio waves (low f) pass through walls that visible light doesn't. But x-rays (high f) also pass through things visible light doesn't. So frequency isn't the determining factor here perhaps?

5. Nov 9, 2012

### ZapperZ

Staff Emeritus
Re: Why is it that lower frequency EM waves are aloud to pass through objects, but hi

But x-rays, which has a higher frequency than visible light, can penetrate through your skin/body, while visible light can't!

So now we have a contradiction to your assertion, which is something that you should have brought up (I'm assuming you are well-familiar with x-rays). So now how would you proceed in your thinking? Is this whole thing really an issue with EM wave, or is this really more of a function of the material that interacts with that EM wave? Remember, there are two parties involved here - the light and the material that it is impinging upon. You seem to have dismissed the latter.

Just because the bride wears all the fancy dress and gets all the attention doesn't mean that you can ignore the groom!

Zz.