What happens when matter and anti-matter collide? Do they just destroy each othe…

Lou Bloomfield Leave a comment

What happens when matter and anti-matter collide? Do they just destroy each other? I thought that matter couldn’t be created or destroyed? – S

As Einstein’s famous formula points out, mass and energy are equivalent in many respects. In most situations, mass is conserved and so is energy. But at the deepest level, it’s actually the sum of those two quantities that’s conserved. When matter and anti-matter collide, they often annihilate one another and their mass/energy is converted into other forms. For example, when an electron and an anti-electron (a positron) collide, they can annihilate to produce two or more photons of light. There is no fundamental law that prevents matter from being created or destroyed but there is a fundamental law that mass/energy must be conserved. In this case, the masses of the electron and positron become energy in the massless photons. Overall, mass/energy has been conserved but what was originally mass has become energy. The fact that when matter and anti-matter annihilate, the product is usually energy, makes this mixture attractive as a possible super-rocket fuel. But don’t hold your breath; anti-matter is incredibly difficult to make or store.

How can we measure magnetic fields or magnetic potentials of solvent atoms that …

Lou Bloomfield Leave a comment

How can we measure magnetic fields or magnetic potentials of solvent atoms that reside interstitially inside solid solutes? — DR, Tampa, FL

You can measure the magnetic fields in which certain atoms reside with the help of nuclear magnetic resonance (NMR). This technique examines the magnetic environment of the atom’s nucleus by determining how much energy it takes to change the orientation of the nucleus. Since the nucleus is itself magnetic, it tends to align with any magnetic field—like a compass. The stronger that magnetic field, the harder it is to flip the nucleus into the wrong direction.

How do Oven Cooking Bags work? I know they are made of heat resistant nylon resi…

Lou Bloomfield Leave a comment

How do Oven Cooking Bags work? I know they are made of heat resistant nylon resin, but can you explain what that means? — HY, Halifax, Nova Scotia

There are two broad classes of plastics: (1) thermoplastics that can melt, at least in principle, and (2) thermosets that can’t melt under any circumstances. Thermoplastics consist of very long but separable molecules and common thermoplastics include polyethylene (milk containers), polystyrene (Styrofoam cups), Nylon (hosiery), and cellulose (cotton and wood fiber). Thermosets consist of very long molecules that have been permanently cross-linked to one another to form one giant molecule. Common thermosets include cross-linked alpha-helix protein (hair) and vulcanized rubber (car tires).

Most common plastic items are made from thermoplastics because these meltable plastics can reshaped easily. But different thermoplastics melt at different temperatures, depending on how strongly their long molecules cling to one another. The plastic in an Oven Cooking Bag is almost certainly a thermoplastic form of Nylon, but one that melts at such a high temperature that it doesn’t change shape in the oven. It’s possible that the Nylon has been cross-linked to form a thermoset, so that it can’t melt at all, but I wouldn’t expect this to be the case.

How does ultrasound detect cracks or imperfections in metal? Is this to do with …

Lou Bloomfield Leave a comment

How does ultrasound detect cracks or imperfections in metal? Is this to do with density or is it just reflecting off surfaces? — PA, Essex, UK

Like all waves, ultrasound reflects whenever it passes from one material to another and experiences a change in speed (or more accurately, a change in impedance). Any inhomogeneity in a metal is likely to change the speed of sound in that metal and will cause some amount of sound reflection. With the proper instruments emitting sound and detecting the reflected sound, it’s possible to image the imperfections. The same technique is used in medical ultrasound to image organs or fetuses, and even to image the insides of the earth.

Is it possible to eat a microwave while you eat food that was cooked in the micr…

Lou Bloomfield Leave a comment

Is it possible to eat a microwave while you eat food that was cooked in the microwave oven? – PTW

Not one that came from the microwave oven. Microwaves are all around us and are completely innocuous. Your body emits weak microwaves all the time, as part of its thermal radiation! Like light, microwaves don’t remain still in objects so you can’t eat one that was put in the food by the oven.

If the condenser in a microwave is bad, what is the most likely reaction the mic…

Lou Bloomfield Leave a comment

If the condenser in a microwave is bad, what is the most likely reaction the microwave generator will exhibit? — IF, Bakersfield, CA

According to a reader, most microwave oven capacitors have fuses in them so that when they fail, they usually become open (they lose all of their ability to store separated charge and behave as a simple open circuit). You’d need a capacitor checker to find this open circuit within the capacitor.

How can we clean the microwave oven? – PTW

Lou Bloomfield Leave a comment

How can we clean the microwave oven? – PTW

Since the cooking chamber of a microwave oven doesn’t get hot, there is no way to make a “self-cleaning” microwave oven. Instead, you have to clean it by hand with a sponge and perhaps a little soapy water. As long as you get the soap or any other cleaning agents out, you can clean the cooking chamber just as you’d clean the top of a stove.

Don’t microwaves penetrate metal at all?

Lou Bloomfield Leave a comment

Don’t microwaves penetrate metal at all? — DR, Tampa, FL

If the metal is a good conductor, then the microwaves don’t penetrate more than a fraction of a millimeter. That’s because the microwave electric fields push on the metal’s mobile electrons and those electrons immediately rearrange in such a way that they cancel the microwave fields inside the metal. Only the skin of the metal responds to the fields and it shields the rest of the metal from the microwaves.

I am interested in finding out if and what materials affect magnetic fields.

Lou Bloomfield Leave a comment

I am interested in finding out if and what materials affect magnetic fields. — HLD, Jacksonville, FL

Magnetic fields are associated with lines of magnetic flux, invisible structures that stretch between north and south magnetic poles or that curve around on themselves to form complete loops. Unless a material has its own north or south magnetic poles, it can’t terminate the magnetic flux lines and can have only small effects on magnetic fields. The few materials that do affect magnetic fields substantially are ones such as iron or steel that are intrinsically magnetic and that can easily develop strong north and south magnetic poles. These magnetic materials can significantly shift the paths of the magnetic flux lines. If you put an iron or steel box in a magnetic field, the flux lines will tend to travel through the walls of the magnetic box. As a result, there will be few magnetic flux lines inside the box and almost no magnetic field. This effect is used to shield sensitive equipment such as the picture tubes in televisions from magnetic fields.