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Todays Mystery Object?

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Martin King 217/07/2018 18:08:32
540 forum posts
171 photos

Hi All,

Just got back from buying a lot of workshop kit and this unusual item was in one of the boxes. I have no idea what it is? Possibly some sort of level???

odditem 1.jpg

odditem 2.jpg

odditem 3.jpg

Seems to have some sort of mirror inside and appears to be very sensitive to movement.

Any thoughts will be most welcome please. Regards, Martin

SillyOldDuffer17/07/2018 18:27:18
3512 forum posts
687 photos

I think its a mirror galvanometer for precisely zeroing a Wheatstone Bridge. A beam of light is bounced off the mirror onto a distant screen to greatly amplify the scale of any movement.

The meter is likely to be very sensitive and best practice is to short the terminals out to dampen any movement in storage. It also has a mechanical clamp.

Dave

SteveW17/07/2018 18:38:08
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107 forum posts
10 photos

Mirror galvanometer to detect balance point on a Wheatstone bridge? Hint on the picture which shows circuit. Clamp stops the device from swinging free and potentially damaging itself in transport or storage.  SOD beat me to it!

Edited By SteveW on 17/07/2018 18:40:03

Mike Poole17/07/2018 18:45:06
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1571 forum posts
41 photos

It may be the works of a spot reflecting galvanometer the main scale and the rest of the box are missing.

 

Mike

Well while I was looking I was beaten to the answer, but it seems to be three votes for a mirror galvanometer.

Edited By Mike Poole on 17/07/2018 18:47:31

Neil Wyatt17/07/2018 18:48:06
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Moderator
15008 forum posts
638 photos
72 articles

It's been done.

Clamp/free locks the movement.

By reflecting a narrow beam off the mirror onto a remote scale it provide an incredibly sensitive way of comparing the ratios of two pairs of resistors.

Neil

Martin King 217/07/2018 19:20:27
540 forum posts
171 photos

Thanks very much to one and all, what a great place this is!

Cheers, Martin

paul rushmer17/07/2018 20:04:34
69 forum posts
10 photos

If my memory is correct that was made by Cambridge Instruments cam in a bridge !!

Paul

larneyin17/07/2018 21:57:02
12 forum posts
18 photos

Used to repair them many years ago

Eyesight was keener and hands steadier then smiley

Howard Lewis18/07/2018 20:21:18
1525 forum posts
2 photos

The wire across the terminals is to short the movement when travelling and minimise pointer movement. Needed, because it is a very sensitive piece of kit. A light beam, reflected off the mirror has no measureable weight or inertia.

A long "pointer" is therefore obtainable for maximum accuracy.

Howard

Neil Wyatt18/07/2018 20:35:12
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15008 forum posts
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Posted by Howard Lewis on 18/07/2018 20:21:18:

A light beam, reflected off the mirror has no measureable weight or inertia.

But it does have momentum

Neil

peak418/07/2018 21:12:23
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626 forum posts
50 photos
Posted by Neil Wyatt on 18/07/2018 20:35:12:
Posted by Howard Lewis on 18/07/2018 20:21:18:

A light beam, reflected off the mirror has no measureable weight or inertia.

But it does have momentum

Neil

As soon as I read this, I thought "Crookes Radiometer" and went to look for a suitable article in order to provide a hyperlink

On reading the above link, I then found that what I'd been taught at school seems to be wrong; I do like learning new things. blush

Bill

Ian P18/07/2018 21:12:39
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1981 forum posts
86 photos
Posted by Neil Wyatt on 18/07/2018 20:35:12:
Posted by Howard Lewis on 18/07/2018 20:21:18:

A light beam, reflected off the mirror has no measureable weight or inertia.

But it does have momentum

Neil

With my pedant hat on... I don't think the light beam has any momentum

Ian P

Frances IoM18/07/2018 21:39:51
539 forum posts
22 photos
Ian
according to James Clerk Maxwell a light beam does have momentum - eg see https://en.wikipedia.org/wiki/Solar_sail
not done it yet19/07/2018 06:19:17
2379 forum posts
11 photos

Let’s think about it from Einstein’s point of view.

E = mc^2

If light actually had zero mass, that equation would always equal zero!

Wave-particle duality applies?

Neil Wyatt19/07/2018 09:40:10
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Moderator
15008 forum posts
638 photos
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Momentum of a photon = frequency x planck constant

www.nasa.gov/mission_pages/tdm/solarsail/index.html

Edited By Neil Wyatt on 19/07/2018 09:45:07

SillyOldDuffer19/07/2018 09:48:13
3512 forum posts
687 photos
Posted by not done it yet on 19/07/2018 06:19:17:

Let’s think about it from Einstein’s point of view.

E = mc^2

...

If only I could!

Can anyone explain how E=mc² is derived?

I understand the root to be evidence from radioactive decay - it was observed that the mass of an unstable element decreases slightly as it emits energy. If Conservation of Mass and Conservation of Energy are both true then the evidence suggests Mass and Energy must be equivalent, perhaps forms of something else. (My brain is starting to overheat!)

I made a promising start on the explanation here. It notes that Energy is measured in Joules, ie kg m² s⁻², which was a step forward for me, but I came unstuck where it says the equation applies only to Invariant Mass, not Relativistic Mass.

Now I'm baffled.

Help!

Dave

michael potts19/07/2018 10:42:58
33 forum posts

The equation E = mc^2 is the first term in an infinite series giving the energy of an object. The second term is

1/2 mv^2 which is the kinetic energy of the object. The other terms are miniscule as all are divided by c^2 and higher powers of c^2. The series derives from the calculation of the kinetic energy of an object. The mass of the object changes as it moves and is calculated by the equation M = M0 / ( 1 - v^2/c^2 )^0.5. M0 is the rest mass of the object, M is the mass of the object moving at a velocity of v, so if the object is moving, its' mass is M0 divided by something that is less than 1 making it more massive, and the moving mass gets larger as the velocity increases. If the velocity of the object reaches the speed of light then the mass is then infinite. In practice if the velocity of the object is less than 10% of the speed of light then normal Newtonian mechanics can be applied with little error.

The mathematics of relativity become very complex very quickly, making an already difficult subject even more impenetrable. Infinite series of terms do not help either.

Radioactive fusion or fission is another issue. Both processes work because the mass of the resultant particle is less than the mass of the starting particle (s). This loss of mass appears as energy, heat,light or kinetic energy of the particles. The amount of energy can be calculated knowing the loss of mass. All the work of measuring the mass of atomic nuclei was carried out after work began to develop atomic weapons during WW 2.

Mike Potts.

Martin King 219/07/2018 11:51:46
540 forum posts
171 photos

Blimey, talk about 'thread drift'! smiley

Martin

SillyOldDuffer19/07/2018 12:12:03
3512 forum posts
687 photos
Posted by michael potts on 19/07/2018 10:42:58:

The equation E = mc^2 is the first term in an infinite series giving the energy of an object. The second term is

1/2 mv^2 which is the kinetic energy of the object. The other terms are miniscule as all are divided by c^2 and higher powers of c^2. The series derives from the calculation of the kinetic energy of an object. The mass of the object changes as it moves and is calculated by the equation M = M0 / ( 1 - v^2/c^2 )^0.5. M0 is the rest mass of the object, M is the mass of the object moving at a velocity of v, so if the object is moving, its' mass is M0 divided by something that is less than 1 making it more massive, and the moving mass gets larger as the velocity increases. If the velocity of the object reaches the speed of light then the mass is then infinite. In practice if the velocity of the object is less than 10% of the speed of light then normal Newtonian mechanics can be applied with little error.

The mathematics of relativity become very complex very quickly, making an already difficult subject even more impenetrable. Infinite series of terms do not help either.

Radioactive fusion or fission is another issue. Both processes work because the mass of the resultant particle is less than the mass of the starting particle (s). This loss of mass appears as energy, heat,light or kinetic energy of the particles. The amount of energy can be calculated knowing the loss of mass. All the work of measuring the mass of atomic nuclei was carried out after work began to develop atomic weapons during WW 2.

Mike Potts.

Thanks Mike, interesting to find my belief that E=mc² started from radioactivity is wrong - 'All the work of measuring the mass of atomic nuclei was carried out after work began to develop atomic weapons during WW 2.' I'm never quite sure if what I learned in my youth was over-simplified and explained badly, or if I was too dim to take it in. Sadly for me, the evidence suggests the latter...

Dave

Cornish Jack19/07/2018 13:39:39
836 forum posts
105 photos

or, ... for Harry Hemsley fans - "What did Horace say, Winnie?"

rgds

Bill

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