What are the differences between jet airplanes and rockets?

Newton's third law of motion holds good for motion of both jet air planes and rocket engines. They move by expelling hot gases opposite to the direction of desired acceleration. The momentum imparted to the gases is exactly opposite to the momentum imparted to the vehicle.

The biggest difference between a jet engine and a rocket lies in their propulsion systems.

 A jet engine works like this: It sucks in air from the front of the engine. This air is burned with the fuel within the engine. The resulting large mass of gas is ejected towards the rear at high velocity, which both propels the airplane forward, and gets more air sucked into the engine. In normal flight, the engines are used to propel the airplane forward. The actual 'uplift' is gained through the wings using the strong flow of the wind. 

A rocket, in contrast, carries both fuel (which may be solid or liquid) and oxygen. Therefore it does not suck in air from the front. All it does is burn the fuel with the oxygen, and eject it at very high velocities backward. This momentum is used to both lift and propel the rocket. There are no wings for uplift. Any wings are for steering purposes. 

In a nut shell, rocket carries its own supply of oxygen for combustion. A jet engine requires oxygen from the atmosphere for combustion, and so cannot operate in the vacuum of space. 

 

How does ice form on a window pane in winter?

Its is related to "relative humidity", which is a measure of the amount of actual water vapor in the air compared to the maximum amount of water vapor the air can hold at a particular temperature. Warmer air can support more water vapor than cold air. As warm air comes in contact with a cold window pane, it's temperature is lowered and the water vapor that it can no longer hold condenses. If the temperature of the pane is below 0°C (32°F). that water freezes to become ice on the window pane.

CHEMICAL RESISTANCE & PHYSICAL PROPERTIES OF SOME PLASTICS

Courtesy: Dyna Labs

What is outgassing in vacuum science?

The generation of gas resulting from the desorption is known as outgassing. The outgassing constant is defined as the rate at which gas appears to emanate from unit area of surface, and is usually measured in units of Torr.Liter.Sec-1.Cm-2.     

If the temperature of the material is raised (baking), the outgasssing rate rises to a peak value.

Together with the acceleration of desorption, heating may also have the effect of causing activated chemisorption of physically adsorbed gas (in particular water vapour), which can then be desorbed only by prolonged heating at much high temperatures.

Chemi-adsorbed water vapor continues to be evolved at temperatures in excess of 300 degC. It should therefore appear that a degassing programme should begin with pumping at room temperature to remove physically adsorbed water vapor, before baking is commenced.

What is desorption?

When a material is placed in Vacuum, the gas which was previously adsorbed begins to desorb i.e. to leave the material.

The desorption is influenced by

1.       Pressure

2.       Temperature

3.       Shape of material

4.       Kind of its surface

The pressure has a basic influence on the desorption phenomenon since according to its tendency of increasing over or decreasing below the equilibrium , the phenomenon of sorption or that of desorption appears.

The temperature has a clear influence on desorption phenomena. Desorption is endothermic, thus it is accelerated by increase of temperature.

The shape of the material influences desorption either if the gas is adsorbed or absorbed.

If the gas is adsorbed, then only the amount of surface is the influencing factor, but if the gas has to diffuse from the interior of the material to the surface, then the third dimension “thickness” is also influencing the rate of desorption. 

ABOUT ELECTROLYTIC CAPACITORS

They provide more capacitance for their size than any other type. Electrolytics all have one thing in common, instead of usual plates separated by a dielectric, the electrolytic capacitor has a metallic anode coated with an oxide film. This outer covering is the dielectric, and a liquid electrolyte acts as a cathode. A second metallic conductor serves primarily as the connection to the liquid cathode, providing an external termination.

In actual practice, porous paper is wrapped around the anode and saturated with the electrolyte to eliminate the spillage problem.

There are two common types of electrolytic capacitors: a)  Aluminum  b) Tantalum

Both employ the same basic principle. The aluminum or Tantalum anode is covered with an oxide film. A suitable liquid or solid electrolyte is the cathode. The Aluminum type is by far the most popular because of its lower cost. The aluminum –oxide film has a very high resistance to current in one direction and has very low resistance to current in opposite direction. In other words, film acts as a dielectric in first instance and as a plate in second case. Because of this electrolytic are polarized. If the designated polarity is not observed, the oxide film on anode will breakdown and migrate to cathode connection, resulting in prompt failure of capacitor.

Electrolytics are described as belonging to one of the three basic families;

Polarized type

This type has one anode, the liquid cathode and a cathode connection. Polarity must be observed.

Semi polarized type

In many energy storage applications a certain amount of current reversal is often encountered. In such cases this type is recommended. In this type, the primary anode has a relatively thick oxide surface. The cathode connection now becomes the secondary anode with a thin oxide surface. Also liquid cathode has a slightly different chemical composition.

Non-polarized

This type is used in audio cross over networks and ac motor starting applications. Here there is a complete reversal of polarity; therefore, two anodes are required. The cathode connection now becomes a second, and equal, anode. Obviously size will be affected. Infact, the third type called nonpolarized is just twice as large as a polarized type of equivalent capacitance and voltage rating.