Infrared Thermometer

[Ralph]

Anyone got recommendations for a infrared thermometer for finding cold spots? I've looked at a few on Amazon and the reviews and error margin seems to make some of them pointless.

[SteamyTea]

I got a cheap one from Lidl.

I would not worry too much about precision and accuracy, you will be using it as a comparator i.e. is this bit hotter than that bit.

[ToughButterCup]

1 hour ago, Ralph said:

...  error margin seems to make some of them pointless.

 

Look for @Jeremy Harris recommendation on this board. I agree with the point above: you're looking for relative temperature difference.

 

In a fit of lust, I bought the Bosch colour thermometer a couple of  years ago.

 

 

Works a treat.

It's good enough to act  as a thermal imager to identify rats 20 meters away.

 

 

Yes, @SteamyTea, yes, I know.

[Russdl]

If you get tempted by the Bosch thermometer you’ll be in the ‘Flir 1 Pro’ price territory. Brilliant bit of kit that attaches to the base of your iPhone (I hear rumours that other types of phone exist as well?)

 

Heres one I made earlier of an open bedroom window. Various temps identified, should be self explanatory. 
 

 

 

[Redbeard]

@Russdl, what was the minus 12.6 degree 'item'? How cold is it in Salisbury at the moment? Had a guess or two but the siting (above a bedroom) seems illogical for my guess.

[ToughButterCup]

9 minutes ago, Russdl said:

If you get tempted by the Bosch thermometer you’ll be in the ‘Flir 1 Pro’ price territory. Brilliant bit of kit that attaches to the base of your iPhone (I hear rumours that other types of phone exist as well?)

 

Heres one I made earlier of an open bedroom window. Various temps identified, should be self explanatory. 
 

 

 

 

Clearer display than the Bosch .................

[Russdl]

@Redbeard that’s the zinc roof and it’s definitely not that cold but the zinc always seems to throw back some weird numbers. I’ve no idea why zinc would do that.
 

Actually, scratch that theory. It’s the sky/deep space maybe it’s a real temperature???

Edited October 5, 2022 by Russdl
When I realised I probably couldn’t have seen the roof from where I was stood taking the picture.

[Radian]

34 minutes ago, Russdl said:

@Redbeard that’s the zinc roof and it’s definitely not that cold but the zinc always seems to throw back some weird numbers. I’ve no idea why zinc would do that. 

You're probably looking at the temperature of the sky. Point an IR thermometer at the sky and it's generally -20 or less. Emissivity also plays a role in that low emissivity surfaces like metals read lower than their surface temperature because the IR sensors only respond to radiation. You can readily see reflections so you may even be seeing a reflection of the sky.

[Russdl]

@Radian yep. Just worked bits of that out (and edited my post)

[SteamyTea]

1 hour ago, Russdl said:

I’ve no idea why zinc would do that.

Ask Einstein, he is to blame.

 https://byjus.com/physics/einsteins-explaination/

[Russdl]

21 minutes ago, SteamyTea said:

Ask Einstein

I can’t!

 

[SteamyTea]

45 minutes ago, Russdl said:

I can’t!

You must have been naughty and had your IP blocked.

 

Einstein's Explanation Of Photoelectric Effect

 

The photoelectric effect is a phenomenon where electrons are emitted from the metal surface when light of sufficient frequency is incident upon it. The concept of the photoelectric effect was first documented in 1887 by Heinrich Hertz and later by Lenard in 1902. But both the observations of the photoelectric effect could not be explained by Maxwell’s electromagnetic wave theory of light. Hertz (who had proved the wave theory) himself did not pursue the matter as he felt sure that it could be explained by the wave theory. However, the concept failed in the following accounts:

 

1. According to the wave theory, energy is uniformly distributed across the wavefront and is dependent only on the intensity of the beam. This implies that the kinetic energy of electrons increases with light intensity. However, the kinetic energy was independent of light intensity.
2. Wave theory says that light of any frequency should be capable of ejecting electrons. But electron emission occurred only for frequencies larger than a threshold frequency (ν₀₎.
3. Since energy is dependent on intensity according to wave theory, the low-intensity light should emit electrons after some time so that the electrons can acquire sufficient energy to get emitted. However, electron emission was spontaneous no matter how small the intensity of light.

Following is the table with links of other experiment related to the photoelectric effect:

Hertz And Lenard’s Observations Of The Photoelectric Effect

Einstein’s Explanation of Photoelectric Effect

Einstein resolved this problem using Planck’s revolutionary idea that light was a particle. The energy carried by each particle of light (called quanta or photon) is dependent on the light’s frequency (ν) as shown:

E = hν

Where h = Planck’s constant = 6.6261 × 10^-34 Js.

Since light is bundled up into photons, Einstein theorized that when a photon falls on the surface of a metal, the entire photon’s energy is transferred to the electron.

A part of this energy is used to remove the electron from the metal atom’s grasp and the rest is given to the ejected electron as kinetic energy. Electrons emitted from underneath the metal surface lose some kinetic energy during the collision. But the surface electrons carry all the kinetic energy imparted by the photon and have the maximum kinetic energy.

We can write this mathematically as:

Energy of photon

= energy required to eject an electron (work function) + Maximum kinetic energy of the electron

E = W + KE

hv = W + KE

KE = hv – w

At the threshold frequency, ν₀ electrons are just ejected and do not have any kinetic energy. Below this frequency, there is no electron emission. Thus, the energy of a photon with this frequency must be the work function of the metal.

w = hv₀

Thus, Maximum kinetic energy equation becomes:

KE = 1/2mv²_max=hv–hv₀

1/2mv²_max=h(v−v₀)

V_max is the maximum kinetic energy of the electron. It is calculated experimentally using the stopping potential. Please read our article on Lenard’s observations to understand this part.

Stopping potential = ev₀ = 1/2mv²_max

Thus, Einstein explained the Photoelectric effect by using the particle nature of light.

The below video is a quick revision of what is photoelectric effect:

[Ralph]

8 hours ago, ToughButterCup said:

 

Look for @Jeremy Harris recommendation on this board. I agree with the point above: you're looking for relative temperature difference.

 

In a fit of lust, I bought the Bosch colour thermometer a couple of  years ago.

 

 

Works a treat.

It's good enough to act  as a thermal imager to identify rats 20 meters away.

 

 

Yes, @SteamyTea, yes, I know.

 

7 hours ago, Russdl said:

If you get tempted by the Bosch thermometer you’ll be in the ‘Flir 1 Pro’ price territory. Brilliant bit of kit that attaches to the base of your iPhone (I hear rumours that other types of phone exist as well?)

 

Heres one I made earlier of an open bedroom window. Various temps identified, should be self explanatory. 
 

 

 

Those are both pretty impressive but jeezo £380 is a bit more than I was thinking of. That FLIR is very nice.