## Why is a Metal Plate “Colder” Than a Plastic Plate?

No, it isn’t!

### What is Cold?

According to the dictionary, a body at a relatively lower temperature, especially when it is compared to the temperature of a human body is described as a colder one. So, any object below the normal human body temperature – about 37 degrees Celsius – is a cold thing. But wait a minute!

When you touch an object, what does it tell you about the temperature of the object? Can you really judge if it is a cold one or a hot one? Unfortunately, our bodies aren’t thermometers, we are not so smart when it comes to judging the temperature. Consider the following case.

A book and a steel plate kept in the same environment for a long time attain the same temperature eventually (it is called thermal equilibrium). This can be checked by using a thermometer on both the objects. But, when people are asked to touch a metal plate and a book, they find the former to be much cooler. You can try this out yourself by touching different materials around you. You’ll see how some things ‘feel colder’ while the others feel warmer. A YouTube channel Vertasium conducted a social experiment to record this on camera. See the video below:

### There is no cold – only heat

So, in the video, ice melts faster, if kept on steel plate than on a plastic plate, even when the steel plate ‘feels colder’. Common sense dictates that the colder thing is supposed to sustain the ice block for a longer time, just like your refrigerator does. So why does the opposite happen?

A better way to understand this ‘contradiction’ (not really a contradiction) can be this:

According to thermodynamics, simply put, everything has heat in it. So, even a cold ice block has some amount of heat stored in it (say, around 273.15 Kelvin or 0 degree Celsius). When one object comes in contact with other object, it loses or gains heat till their temperatures get equal or till they attain ‘thermal equilibrium’. Which object loses heat and which one gains it, is decided by their relative temperatures. In case of ice and steel, ice has a lower temperature than steel (assuming it isn’t already freezing out there). Therefore, here, ice gains heat from steel till they attain the same temperature and ice melts.

Side note: The ice is also in contact with a relatively ‘hotter’ atmosphere. Hence, it gains heat from there also. In this case, we are only concerned about the steel and ice interaction.

### Why does it melt faster on steel?

There is a particular property which depends on the kind of material and is called thermal conductivity. This is the parameter which decides which objects lose heat quicker and which ones do it slower.

Here, for instance, steel has a higher thermal conductivity than plastic. Hence, the steel plate gives away heat to the ice block faster than a plastic block does. As a result, ice melts faster on a steel plate than on a plastic one.

Incidentally, this effect can also be used to explain why one plate feels colder than the other, in our hands. Think of it like this, the ice is replaced by our hand. So, a steel plate, due to its better thermal conductivity, draws heat faster from our hand than a plastic plate. This makes us feel that the steel plate is colder than the plastic one.

As checked by a thermometer, both the plates have the same temperature, our bodies are only fooled into believing that the thing we feel is temperature; it isn’t. None of the plates is actually colder than the other (according to the dictionary – see first paragraph). We don’t feel the temperature. What we feel is actually the rate of heat being drawn away from our hand. Faster an object draws heat, the colder it feels.

## Understanding the Impending Helium Crisis

### There is too much Helium?

Helium is the second most abundant element in the observable universe, present at about 24% of the total elemental mass. Helium is also the second lightest element. So, 24% by mass is too huge a mass for a single light element. It equates to a measure that is probably millions of times more than what humanity could use up in millions of years. Close to about 12 times the mass of all the heavier elements combined, this element will almost never run out. But, that is only when we talk about the universe. Back in Earth, it is completely a different story.

### Helium sources for us

On Earth, Helium is relatively rare. It amounts to only a 0.00052% volume of the earth’s atmosphere. Although 0.00052% is not too less, you also can’t consider it as an abundant element. Moreover, extracting Helium from air is almost 10,000 times more costly than fractional distillation (mentioned in the next paragraph). So, all that Helium in air is nearly useless to us till better methods of extraction are invented.
Thankfully, Helium is also present under the surface of the earth. The source of this kind of deposit is, radioactive decays which take place down there. It mixes with the natural gas and is lost to space, if released into the atmosphere. It is separated from natural gas using a process called fractional distillation – The best process to make Helium.

The largest known underground reserve estimated to contain about 10 billion cubic feet of Helium is a federal reserve (mostly under Texas and Kansas). For years US reserves had been the largest global suppliers of Helium (90%). Even today, these reserves contribute to more than 35% of the total global supply. The price of Helium coming from this source has remained almost unchanged for a long time. While during the same period (10 years) privately held Helium prices have tripled. The gap in prices is increasing every day, creating a big distortion in the market.

### Helium Usage

Uses of Helium range from manufacturing smart phone screens (all LCD screens) to optical fibers (Internet cables) to health care (MRI scanners) to scientific research etc. [Uses of Helium]

### The Problem

Since Helium has been made artificially cheap due to the Helium privatization act, it is popularly believed to be a cheap gas and is wasted a lot. Instead of using it up for important things, we consume it by filling up party balloons, distort voices and other entertaining activities. In fact, the warning issued by the Nobel Prize winner Robert Richardson that Helium could be depleted within a generation, seems to have had no effect on us. We still continue to waste a lot of Helium, release it into the air and keep losing it forever. Not many realize that it is a non-renewable resource.

We have almost reached a crisis already, but it was temporarily averted by the congress. In the future, after about 6-7 years, when the Federal Reserve stops supplying it (at below-market prices), it could be a big problem. I’m not very optimistic about market adjusting within such a small span either. In under a decade, we’ll probably see smart-phone prices, optical fiber prices and health care (MRI scans etc.) prices shoot up precipitously due to this artificial market distortion, if we do not start using Helium properly.

## Plasma Speakers

###### by Anupum Pant

Not many would have heard of speakers other than those which use magnetic materials to produce sound. But if you still haven’t heard about Plasma speakers or ionic plasma tweeters, you are really missing something great. Read on for more.

I talked about sound a few days back and mentioned that it is something that propagates through a medium due to pressure changes. Normally, magnetic speakers create these pressure waves by moving a diaphragm with the help of a varying magnetic field. But, plasma speakers do this by varying the air pressure through a high energy electric arc. This arc is produced by ionizing the gas present in between two terminals (ionizing reduces the electrical resistance of air which creates a visible arc).

These speakers use an extremely high energy arc which also increases the temperature of surrounding volume of gas to very high levels. So, before learning anything about them, the first thing you have to know is that these seemingly harmless things can kill you.

### The Dangers

Plasma speakers are not toys. Old men, people with heart problems, kids etc should stay away from them. Even if an adult is handling them, they need to be informed about what they are doing first. It is better to have someone close who knows well, how these things work. Although the commercially available speakers are fairly safe, DIY kits can prove to be fatal. The kind of dangers involved with these devices:

1. The electric discharge – Think of it as a lightning. The dangerous high voltage device has the potential to kill you, if any of your body part comes close. Keep all bodily parts away.

2. Gas danger – The constant supply of ozone used for this project can actually be much more dangerous than the electric arc. Ozone used in this project, silently increases in concentration which can be fatal. It is important to keep the room well ventilated.

A few more things about them

Invented by WIlliam Duddells in the year 1900 these are not speakers, but tweeters. That means, that there will be no window cracking bass that is going to come out of them. Unlike magnetic diaphragms, the arcs have no weight and are able to produce a very crystal clear sound by moving back and forth very quickly. See the video below.

They work by changing temperature inside the gas chamber which makes them go red to purple as the frequencies of a song change. However, an un-modulated arc will just produce noise, something like you hear at first in the video. Also, they need a constant supply of Helium and Ozone coming into the chamber. These gases get ionized inside to produce the arc.