Induction hobs - a question

[Andrew2]

Ever since they arrived on the scene, I thought I knew how induction hobs worked - that is by causing rapid heating of the base of the pan by induced eddy currents and cooking the food contained within simply by 'ordinary' heat from the pan itself. So imagine my surprise when I read (in The Spectator, no less) the following:

'The induction saucepan gets hot, but only because the food inside it does. That is what thrills anyone who has a primarily scientific outlook on the world. Gazing down into the magnetic saucepan, having jabbed first up to ‘nine’, you can remind yourself that the contents are turning from raw to cooked not because something hot is underneath them, but because an alternating eddy current is making a fluctuating magnetic field that, indirectly, is producing heat.'

So according to the author, the food is heated directly by the induction field, rather like in a microwave oven, and the pan gets hot only because the food heats it. Surely some mistake?

[kellys_eye]

The lack of scientific competence seems to be getting more prevelant amongst the media outlets in my experience.

Hardly worth the effort of correcting them. They do far worse on other subjects and similarly don't bother with corrections.

[Cobaltblue]

Hmm apparently radio waves don't travel in a vacuum.

The level of scientific incompetence in the media is frightening.

Cheers

Mike T

[The Philpott]

Every bit as misinformed as the incident where sound waves and radio waves got thoroughly muddled up. The Spectator needs to go to specsavers. (other opticians are available)

I think they were muddling microwaves with induction hobs here..

Dave

[Radio Wrangler]

Did they put a name to the author of that piece?

I just popped into my kitchen and put an empty pan on mine. No food inside so therefore no heat so therefore the pan couldn't get hot?

Simple experiment, good science! Result: The spectator must be a bunch of fools.

I was going to comment that some publications have less connection with reality than others, but didn't the BBC get caught out quite recently as well.

David

[Andrew2]

The article is by Ysenda Maxtone Graham. Full article here:

https://www.spectator.co.uk/2019/02/...y-competition/

I've been a Spectator reader for years and find it an intelligent publication, but this article seems spectacularly (!) ill informed. I would have thought the sub editor would have checked. Perhaps I'm old fashioned.

Pure drivel, not a bit of understanding at all. No wonder moulded on plugs are so popular. I see myself having to work until I drop because of the lack of engineers.

[m0cemdave]

Originally Posted by Andrew2

I would have thought the sub editor would have checked.

I think the print media have been cost-cutting so drastically in recent years that sub editors have been driven to near extinction.
Private Eye (which I find a far more reliable and accurate organ than the Spectator) often republish other people's bloopers under the heading "Bonfire of the Subs".

[Nymrod121]

I seem to recall from a conversation with gezza123 a few years back that he had experience of/within the induction hob business - ? - if so, hopefully he can give some input here.
Best wishes
Guy

[broadgage]

Induction hobs heat the food by the pan getting hot, due to eddy currents induced therein.
That is why conductive pans must be used.

If the food is placed in a non conductive vessel of say Pyrex then it wont heat.

Microwaves by contrast DO directly heat the food and vessel containing the food only gets heated by conduction/radiated heat from the hot food, or by the condensation of steam emitted by the hot food.

[G4YVM David]

Originally Posted by Radio Wrangler

Did they put a name to the author of that piece?

I just popped into my kitchen and put an empty pan on mine. No food inside so therefore no heat so therefore the pan couldn't get hot?

Simple experiment, good science! Result: The spectator must be a bunch of fools.

I was going to comment that some publications have less connection with reality than others, but didn't the BBC get caught out quite recently as well.

David

A true scientist would have done a double blind. Put the food on the job with no pan (I will allow glass) and see what happens...😊

[Andrew2]

Originally Posted by broadgage

Induction hobs heat the food by the pan getting hot, due to eddy currents induced therein.
That is why conductive pans must be used.

If the food is placed in a non conductive vessel of say Pyrex then it wont heat.

Microwaves by contrast DO directly heat the food and vessel containing the food only gets heated by conduction/radiated heat from the hot food, or by the condensation of steam emitted by the hot food.

Oh we're all agreed on that, Broadgage. This post was just to point out the lack of understanding in the article.

[kellys_eye]

Not necessarily 'conductive'. Aluminium is conductive but won't work on an induction hob.

[Radio Wrangler]

Done.

One potato croquette stood directly on hob surface. One more placed in a pyrex basin. The hob tries for ten seconds, decides there's nothing there and stops.

So I put a pan of water somewhat offset one one hob area and the same potato croquette beside it. Brought pan to boil, croquette not defrosted. Selected 'turbo'... water in pan boiling violently, pan buzzing from the field, croquette surface defrosting on side nearest pan, seemingly from radiated heat.

Hmmm It's one thing to complain to an editor, it's another to ask him how he could prove that the rest of his output is any better.

David

[G4YVM David]

Ah very good.

Does the induction obey inverse square law inasmuch as it would still heat a pot stood off by an inch, say, on wooden blocks or does it need really close contact?

[vidjoman]

The manual that came with my hob says NOT to use a copper bottomed pan even if the inside of the pan is iron/steel etc.

We have a stainless steel pressure cooker that tends to dribble condensation down the side from the handle and to keep it clean we used a paper towel under that side of the pan to mop up the water as the food cooks. Could use a cloth as well as it won't burn. Don't try that on a gas or normal electric hob or it will catch fire.

There are some aluminium pans, mostly frying pans, that can be used as they have a stainless plate fitted within the base. They are not as efficient. Stainless steel pans will normally have an aluminium layer sandwiched between 2 steel sheets on the base as the stainless does not distribute the heat very evenly and the ali layer helps to spread the heat.

[Radio Wrangler]

Fairly close contact.

To show visitors you can cook in a pan with a newspaper between it and the the hob. To see if microwave things had any effect (well, for the joke really) I used a spread-open copy of Dubus once.

An inch off and the hob will sense the pan's not there and shut down.

With the rather low heat in the interface between pan and hob, cooking with a pan whose underside is wet produces pops as steam bubbles are ejected from under it.

I definitely wouldn't go back to any other sort of hob.

Perhaps using it as a hob protector may be a better use for the Spectator than reading it.

David

[G4YVM David]

I like the lack of residual heat. The first job I have used was last year...a very expensive ceramic job which stayed very hot even though it was black. Awful risk.

[G8HQP Dave]

but because an alternating eddy current is making a fluctuating magnetic field that, indirectly, is producing heat

That bit is back to front too, quite apart from where this action takes place. It is the magnetic field which makes the eddy current.

New Scientist used to have a section listing these bloopers; maybe it still does?

[Graham G3ZVT]

So this one joins the other kitchen science myths, like microwaves cook food from the inside out, and 2,400MHz is the "resonant frequency of water molecules".