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Showing posts from 2015

### The Cathode Ray Oscilloscope

Introduction  The following should give the student some familiarisation with the function and uses of the cathode ray oscilloscope (C.R.O.).

Consider a simple sine wave electrical signal from some source as in Fig. 1a. If we can arrange things so that this sinusoidal voltage is applied to two horizontal conducting plates then in the region between these plates, the electric field will be alternating with period T seconds. It will increase in strength to a maximum, decrease to zero, turn over, and increase in the opposite direction to an equal maximum, then decrease to zero again, in each period of time T.

Now, if there is a beam of charged particles (electrons) streaming between these horizontal plates, the oscillating electric field there will bend the beam first up, then down, then back to the undeflected position in each time period T. Further, if the beam strikes a plate of material which fluoresces, one would see a spot of light on this plate (screen) which moves vertically up …

### Does water swirl counter-clockwise in the Southern Hemisphere?

Answer:Yes and no. When applied to toilets and sinks, this is one of those “too good to be true” science factoids, I’m afraid. But it does apply in some situations.

The myth goes that if you flush a toilet in Australia the water swirls down the drain the opposite way than in the northern hemisphere, due the Coriolis effect (an apparent force which describes how objects veer to the left or right when traveling on something that’s rotating — see the link above for a good visualization of this).

If there were no other forces on that water in the sink or toilet, that would be true. The Coriolis effect does actually make hurricanes rotate the opposite direction in the two hemispheres. But for toilets and sinks it’s another story. The toilet myth is easy to dispell — just peek around the rim of the toilet and you’ll see that the water is jetted into the bowl at an angle, which determines the direction the water swirls. Sinks, however, are a little more tricky.

I’ve heard of charlatans who …

### Transformer and Hysteresis

Transformer Hysteresis Losses are caused because of the friction of the molecules against the flow of the magnetic lines of force required to magnetise the core, which are constantly changing in value and direction first in one direction and then the other due to the influence of the sinusoidal supply voltage.

This molecular friction causes heat to be developed which represents an energy loss to the transformer. Excessive heat loss can overtime shorten the life of the insulating materials used in the manufacture of the windings and structures. Therefore, cooling of a transformer is important.

Also, transformers are designed to operate at a particular supply frequency. Lowering the frequency of the supply will result in increased hysteresis and higher temperature in the iron core. So reducing the supply frequency from 60 Hertz to 50 Hertz will raise the amount of hysteresis present, decreased the VA capacity of the transformer.

### Frogs Levitate in Strong Magnetic Field

Some things like iron nails are known for their magnetic properties, but why should frogs levitate in a magnetic field? The trick is to get the magnetic field right – you can’t just use any old bar magnet to make a frog levitate.

Frogs, like everything around and inside us, are made up of millions and billions of atoms. Each of these atoms contains electrons that whizz around a central nucleus, but when atoms are in a magnetic field, the electrons shift their orbits slightly. These shifts give the atoms their own magnetic field so when a frog is put in a very strong magnetic field, it is essentially made up of lots of tiny magnets. And there’s nothing special about frogs. All materials – including strawberries, water and gold – are ‘diamagnetic’ to some extent, but some are more convenient to levitate than others.

Frogs are convenient not only because they have a high water content, which is a good diamagnetic material, but also because they fit easily inside a tube-shaped Bitter ele…

### Have you ever been on a train going through a tunnel or a plane and your ears pop? Why does this happen?

A: Inside your ear there is a pocket of air. This pocket is normally at the same pressure as the air outside your ear to help you hear, but if the air pressure around you changes, you feel the air pushing on your eardrum. Your ear has a small tube for equalising the pressure between the inside and outside of the ear that is opened when you swallow and when the pressure is equalised you often feel a pop.

In a plane, the high altitude means the air is thinner and although planes are pressurised, the air pressure is still much less than on the surface. This difference in air pressure can be felt by the ears, particularly on takeoff and landing when changes in altitude make the pressure difference happen more quickly.

The train in a tunnel is slightly different. When the train enters the tunnel it squeezes the air in front of the train creating high pressure in the cabin and you sense this change in pressure.

There are some ways to equalise the pressure between the inside and outside of …