304. Q. & A.s SCI. & TECH. – 15

Q. &  A.s  ‑‑‑  SCI.  &  TECH. – 15

401Q  What are the uses of harmonic currents?

Most power systems can accommodate a certain level of harmonic currents but will

experience problems when harmonics become a significant component of the overall load.

As these higher frequency harmonic currents flow through the power system, they can

cause communication errors, overheating and hardware damage, such as:

• Overheating of electrical distribution equipment, cables, transformers, standby

generators, etc.

• High voltages and circulating currents caused by harmonic resonance

• Equipment malfunctions due to excessive voltage distortion

• Increased internal energy losses in connected equipment, causing component failure

and shortened life span

• False tripping of branch circuit breakers

• Metering errors

• Fires in wiring and distribution systems

• Generator failures

• Crest factors and related problems

• Lower system power factor, resulting in penalties on monthly utility bills

402Q.  Answer split versus window AC

Split AC is usually whole house where the condenser is outside and the evaporator is in the furnace. Window AC is simply that where it is all in one unit for one or two rooms.

403 Q.  Reasons Why Silicon Is the Semiconductor for Electronics

A silicon wafer contains millions of transistors.

silicon holds up well under heat and is an inexpensive material.

Semiconductors

A few elements -- silicon, germanium, and arsenic -- make good semiconductors.

They are neither good conductors nor good insulators but fall in between the two extremes.

A semiconductor becomes useful when mixed with traces of other elements, such as boron and phosphorus, in a process called "doping."

The resulting substance "prefers" either positive or negative electrical charges but not both.

Transistors, the foundation of the electronics revolution, are made of sandwiched layers of doped silicon.

Heat Tolerance

Silicon does have heat-dependent electrical characteristics, requiring cooling fans and heat sinks for some applications.

Abundance

It is easy to obtain, making raw materials inexpensive.

Germanium, on the other hand, is relatively rare, amounting to 1400 parts per billion (ppb) of the Earth.

Arsenic, the other common semiconductor, is somewhat more common than germanium at 2100 ppb.

Leakage Current

Silicon diodes leak far less than those made of germanium, producing circuits with better efficiency.

Silicon Production

Scientists and engineers understood that silicon transistors had better characteristics;

404Q.  Transmission electron microscopy

Transmission electron microscopy (TEM) is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through. An image is formed from the interaction of the electrons transmitted through the specimen; the image is magnified and focused onto an imaging device, such as a fluorescent screen, on a layer of photographic film, or to be detected by a sensor such as a CCD camera.

TEMs find application in cancer research, virology, materials science as well as pollution, nanotechnology, and semiconductor research.

405Q.  scanning transmission electron microscopy (STEM)

With the development of TEM, the associated technique of scanning transmission electron microscopy (STEM) was re-investigated and did not become developed until the 1970s, with Albert Crewe at the University of Chicago developing the field emission gun and adding a high quality objective lens to create the modern STEM.

406Q.  Water vapor is present in

• Atmosphere of Mercury: 3.4%, and large amounts of water in Mercury's exosphere
• Atmosphere of Venus: 0.002%
• Earth's atmosphere: ~0.40% over full atmosphere, typically 1–4% at surface
• Atmosphere of Mars: 0.03%
• Atmosphere of Jupiter: 0.0004%
• Atmosphere of Saturn – in ices only
• Enceladus (moon of Saturn): 91%
• exoplanets known as HD 189733 b and HD 209458 b.

Liquid water is present on

• Earth: 71% of surface
• Europa: 100 km deep subsurface ocean

407Q.  Water ice is present on

• Earth – mainly as ice sheets
• polar ice caps on Mars
• Moon
• Titan
• Europa
• Saturn's rings
• Enceladus
• Pluto and Charon
• Comets and comet source populations (Kuiper belt and Oort cloud objects).

408Q. What are different types of rays?

A few of them are:
-- Channel 4 TV
-- microwave oven cooking power
-- heat
-- green light
-- the sun's tanning rays
-- the dentist's X-rays
-- gamma rays
-- cosmic rays

409Q. Why should we be thankful to Steve Jobs?

1.      The IPOD and ITunes

2.      Focusing on design

3.      Inspiring others

4.      The IPAD

5.      Wowing investors

6.      Being a visionary

7.      Forcing other corporate giants to be innovative

8.      For proving that a dramatic turnaround can be possible

9.      Boosting employment

10.  Money secondary

410Q. What are different estates called?

It was first used in 18^th C, in France.

1.      1^st Estate  is  Religious leaders/clergy

2.      2^nd  Estate  is Nobles

3.      3^rd Estate is Poor People

4.      4^th Estate Media

5.      5^th Estate is Journalism

411Q. Why new drugs are created for  treatment?

1.      Every 10 years body resistance changed

2.      “mg” value differs

3.      For changing body, molecule is also to be changed

4.      Old drugs are deleted and new ones are to be introduced eg. actifed

5.      Sustainable release  tabs are introduced so single type ones are replaced

6.      The need of one chemical in different forms is needed

7.      If blood group changes

8.      If artificial limb is introduced  etc.

412Q. Why frequency drifts?

1.      Component aging

2.      Environmental changes

3.      Voltage fluctuations

4.      Improper tuning

5.      Temperature changes

6.      Illegal interference

7.      Adjacent channel

413Q. Why  frequency can be controlled?

1.      By placing a crystal of that frequency

2.      Maintenance of component

3.      A/C

414Q. What are bad cholesterol?

Cholesterol can’t dissolve in the blood. LDL = Low density lipoprotein is bad cholesterol.

1.      It covers walls of arteries that feed the brain and heart

2.      Can increase heart disease

3.      Palm oil has highest cholesterol

4.      It cannot be removed from blood

5.      It is accumulated by unwanted oily, creamy, sugar, foods having high carbohydrates etc.

6.      It increases over weight, physical inactivity, cigarettes, alcohol, high carbon etc.

415Q. What is good cholesterol?

1.      HDL = high density lipoprotein is called good cholesterol

2.      It is 1/3^rd of blood

3.      It takes it from liver

4.      It can be removed from body

5.      It is accumulated by natural food

416Q. Why ocean water is salty?

All the living things of ocean use all types of minerals for their some or other use. What is not need by all is sodium chloride. That is why ocean is salty.

417Q. Why doesn’t blood clot?

For clotting of blood plateletes are required. They are called thrombocytes. In 1 cu.mm.s generally 150000 – 350000 are observed. If the number decreases to less than 66000 they won’t clot. This disease is called purpura.

418Q. what is called stone in kidney?

Calcium oxalate, calcium phosphate

Laxalo bacter phyarmy is bacteria that produces enzymes which produces enzymes that break.

If those enzymes are artificially made it can be broken.

419Q. How can so many channels be transmitted from a single wire?

1.      Frequency division multiplexing

2.      Sine waves are of 

[1] different magnitudes

[2] different frequencies

[3] different harmonics

420Q. Why the flesh of farm animals should not be eaten?

1.      Powerful antibiotics are used to avoid diseases

2.      More flesh hormones are given

3.      Feed chemicals cannot be digested

4.      Due to high power drugs used, we get plenty of digestive disorders

421Q. What does CIGARETTE stand for?

C         cancer in lungs

I           ischaemic disease

G         gastric ulcer

A          atherosclerosis

R         respiratory disorders

E          emphysema

T          Thromboembolic disease

T          TB

E          eye sight

422Q. After  100^o C temperature does not rise. Why?

Whatever heat that we supply  is utilised to change the state of liquid into vapour. That is why temperature does not rise.

423Q. When a bulb breaks why there will be sound?

Inside the bulb  there is vacuum. When a bulb breaks air rushes to fill the gap where there is vacuum. So sound is heard.

424Q. When we sprinkle water on hot bulb or heat a glass tumbler it breaks. Why?

Glass is bad conductor of heat. When we sprinkle water on a hot bulb, it is due uneven  expansion of heat of the surface. It makes it break.

425Q. Why do mountain climbers cook food in low pressure?

At higher places water boils at low temperatures. So food cannot be cooked. To avoid this the mountaineers carry pressure cookers to cook food.

303. Q. & A.s SCI. & TECH. – 14

Q. &  A.s  ‑‑‑  SCI.  &  TECH. – 14

371Q. Problems of Nuclear Reactors

Concerns about the safety of nuclear fission reactors include the possibility of radiation-releasing nuclear accidents, the problems of radioactive waste disposal, and the possibility of contributing to nuclear weapon proliferation.

Although most technical analyses have rated nuclear electricity generation as comparable in safety to coal-powered generation, the low public confidence in nuclear power has blocked further development of nuclear power in the United States. No new nuclear power plants have been ordered since the Three Mile Island accident, and some partially completed projects have been abandoned. As of 1990 about 20% of electricity in the U.S. was generated by nuclear plants, compared to about 75% in France.

372Q. Reactor Accidents

The nuclear accident at Chernobyl was the worst nuclear accident to date, spewing about 100 million Curies of radioactive material into the environment. By contrast, the accident at Three Mile Island released only some 15 Curies. Though its health effects were minimal, Three Mile Island did perhaps irreparable damage to the level of public confidence in nuclear reactors for electric power production in the United States.

Preceding these two high-profile accidents are a number of nuclear accidents with radiation release. These include accidents at the Fermi I reactor near Detroit, at the NRX reactor at Chalk River, Canada, at the Windscale reactor in England, and the SL-1 Reactor at Idaho Falls.

373Q. Radioactive Waste Disposal

The nuclear fission of uranium-235 produces large quantities of intermediate mass radioisotopes. The mass distribution of these radioisotopes peaks at about mass numbers 95 and 137 , and most of them are radioactive. The most dangerous for environmental release are probably cesium and strontium because of their intermediate half-lives and propensity for reconcentration in the food chain.

When spent fuel assemblies are removed from nuclear reactors, they are transported to "swimming pool" storage facilities to dissipate the heat of decay of short-lived isotopes as well as for isolation from the environment. The long term disposal of these wastes remains a major problem. It was assumed that these wastes would be encased in glass and placed in geologic disposal sites in underground salt domes. The site at Yucca Mountain was chosen as a first site,

374Q. Nuclear Weapons Proliferation

One concern about nuclear reactors is that the fuel could be diverted for the production of nuclear weapons. While the the uranium fuel is enriched to only 3-5% and could not easily be further separated to the >90% U-235 needed to produce a bomb, the spent fuel elements contain plutonium-239. The plutonium could be separated chemically and diverted to nuclear weapons production. Security concerns about the plutonium has thus far blocked any reprocessing of fuel from nuclear power plants.

A similar concern exists for fast breeder reactors, where the breeding process produces plutonium-239 for future generations of reactors.

375Q What is top quark ?

It is 200 times massive than proton. It consists an entire mass of gold Top quark consists 174 billion e.v.  It is the heavitiest ever created. It was formulated in 1960.  Anti protons led to top quark.

376Q. What do you mean by good cholesterol and bad cholesterol?

Cholesterol can't dissolve in the blood. It has to be transported to and from the cells by carriers called lipoproteins. Low-density lipoprotein, or LDL, is known as "bad" cholesterol. High-density lipoprotein, or HDL, is known as "good" cholesterol. 

These two types of lipids, along with triglycerides and Lp(a) cholesterol, make up your total cholesterol count, which can be determined through a blood test.

LDL (Bad) Cholesterol
        When too much LDL (bad) cholesterol circulates in the blood, it can slowly build up in the inner walls of the arteries that feed the heart and brain. Together with other substances, it can form plaque, a thick, hard deposit that can narrow the arteries and make them less flexible. This condition is known as atherosclerosis. If a clot forms and blocks a narrowed artery, heart attack or stroke can result. Palm oil food items very high.

HDL (Good) Cholesterol
        About one-fourth to one-third of blood cholesterol is carried by high-density lipoprotein (HDL). HDL cholesterol is known as "good" cholesterol, because high levels of HDL seem to protect against heart attack.

Low levels of HDL (less than 40 mg/dL) also increase the risk of heart disease.

Medical experts think that HDL tends to carry cholesterol away from the arteries and back to the liver, where it's passed from the body.

Some experts believe that HDL removes excess cholesterol from arterial plaque, slowing its buildup.

Triglycerides
Triglyceride is a form of fat made in the body.

Elevated triglycerides can be due to overweight/obesity, physical inactivity, cigarette smoking, excess alcohol consumption and a diet very high in carbohydrates .

(60 percent of total calories or more).

People with high triglycerides often have a high total cholesterol level, including a high LDL (bad) level and a low HDL (good) level.

Many people with heart disease and/or diabetes also have high triglyceride levels.

Lp(a) Cholesterol
Lp(a) is a genetic variation of LDL (bad) cholesterol. A high level of Lp(a) is a significant risk factor for the premature development of fatty deposits in arteries. Lp(a) isn't fully understood, but it may interact with substances found in artery walls and contribute to the buildup of fatty deposits.

377Q. What are the differences of Petrol and Diesel?

PETROL	DIESEL
1.      Ignition byt spark plug	1.      No spark plug is required.
2.      During in take stroke petrol and air mixture is simultaneously introduced	2] in the intake stage air is sucked in the cylinders where it is compressed to 1/16th of its original bolume
3.      Air is not required to be preheated.	3] it is to be heated.
4.      Plug ignites the fuel air mixture	4] no

378Q. Write the differences of TV Screen and Computer monitor?

TV	Computer
1] Broadcast	1] CPU
2] 6 MHz pixels	2] 15 MHz bits
3] Fixed 15.6 KHz	3] 15 to 155 KHZ scanning
4] Modulation and demodulation	4] nothing

379Q. Why Frequency is drifted?

Frequency drift is An undesired progressive change in frequency with time.

In electrical engineering, and particularly in telecommunications, frequency drift is an unintended and generally arbitrary offset of an oscillator from its nominal frequency.

1] Frequency drift can be caused by component aging 

2] Environmental changes.

3] Voltage fluctuations

4] improper tuning

5] temperature fluctuations

6] drift into an adjacent channel,

7] causing illegal interference.

Note:- Frequency drift may be in either direction (higher or lower frequency) and is not necessarily linear.

380Q How to stabilise frequency fluction?

A temperature-compensated, voltage-controlled crystal oscillator (TCVCXO) is normally used for frequency modulation.

381Q. What are the failures of UNO?

UNO is called the costliest dust bin of the world. For what purpose it is established, it failed. It is for maintaining the piece of the world. Except that everything is there.

It could  not stop the II World War.

It could not stop the Vietnam war.

It could not stop the Korea war.

It could not stop the gulf war.

It could not stop the collapse of AIG, ENRON, …

And many more.

382Q. What is oscillating universe theory?

      The present universe is expanding. It  does not spread out unlimitedly. There comes a time when the expanding stops and starts contracting.  That contracting will meet upto a point. This to and fro process is done. This is called oscillating theory of universe.

383Q. What is mono-polarity?

      Before and after I world war, England, Germany, Italy, France…etc countries dominated the world. It was called poly-polar world.

      Before,  during and for sometime after II World War, USA and USSR dominated the world.

      After the Ghorbhachev, USSR was collapsed. USSR became only Russia.

      Then on wards USA has been playing a vital role in the world politics, finance, decision making, etc. that is why it is called mono-polar world.

384Q. Can we store lightening ?

Would this be a viable way to store lightning?
What would make the best insulator/dielectric?

      Some liquid insulator, a noble gas, or just a vacuum? (I am leaning towards vacuum)
If you cannot predict the charge deposited by lightning, how can you adjust your wonder capacitor?

      Once arcing in a capacitor began, it's too late to adjust anything. Usually, lightnings last for less than 1 sec. Why would you want to store lightning? Despite impressive voltages, power of a lightning isn't that great.

      Capacitors are very lousy vessels for energy storage (low energy density=huge sizes of capacitors to store practically significant amounts of energy). That's why cars, submarines.... have chemical batteries for the energy storage instead of capacitors.

      I don’t really have a reason to store lightning; it is just a concept for discussion and thought.
      I know chemical batteries are better at storing energy, but how do you store a lightning bolt directly into a battery? The chemical reaction would not be a happy one.

      Instead of solutions thousands of questions arise.

.

[ OR ]

.

Why can't we store the electricity of lightning?

      No. We can’t store lightning electricity because this electricity is at too high potential that no device can store it. 

      It will burnout if it tries to, by relation Q=CV where Q is charge and C is capacitance V is potential of light for a quantity of charge at given potential.

      We can find the capacitance required and capacitance above 1Farad can ionize air and all charge goes to ground but earth can bear it because its potential is zero and capacitance nearly infinite because of such a large radius

385Q. What is the temperature of a star?

The color of a star's visible light indicates its surface temperature: a relatively cool star glows red (longer wavelength), and very hot ones glow bluish-white or even blue (shorter wavelengths).

• Blue                             more than        30,000 °Kelvin
• Blue to blue white                                10,000 to 30,000 °Kelvin
• White                                                   7,500 to 10,000 °Kelvin
• Yellowish White                                   6,000 to 7,500 °Kelvin
• Yellow                                                             5,200 to 6,000 °Kelvin
• Orange                                                3,700 to 5,200 °Kelvin
• Red                                                      1,000 to 3,700 °Kelvin
• Brown                                     less than          1,000 °Kelvin
• Black                           close to            0 °Kelvin

386Q. Why can’t audio signal disturb the video signal in a TV?

1.      Channel to channel  the difference is 6 MHz.

2.      Audio signal to video signal the difference is 4.5 MHz.

3.      Audio is FM modulated and video is AM modulated.

4.      Channels cannot be tuned.

That is  why audio cannot disturb video in TV transmission

387Q. Why star delta starter is preferred with induction motor?

Star delta starter is preferred with induction motor due to following reasons:
• Starting current is reduced 3-4 times of the direct current due to which voltage drops and hence it causes less losses.
• Star delta starter circuit comes in circuit first during starting of motor, which reduces voltage 3 times, that is why current also reduces up to 3 times and hence less motor burning is caused.
• In addition, starting torque is increased and it prevents the damage of motor winding.

388Q. State the difference between generator and alternator

Generator and alternator are two devices, which converts mechanical energy into electrical energy. Both have the same principle of electromagnetic induction, the only difference is that their construction. Generator persists stationary magnetic field and rotating conductor which rolls on the armature with slip rings and brushes riding against each other, hence it converts the induced emf into dc current for external load whereas an alternator has a stationary armature and rotating magnetic field for high voltages but for low voltage output rotating armature and stationary magnetic field is used.

389Q. Why AC systems are preferred over DC systems?

Due to following reasons, AC systems are preferred over DC systems:
a. It is easy to maintain and change the voltage of AC electricity for transmission and distribution.
b. Plant cost for AC transmission (circuit breakers, transformers etc) is much lower than the equivalent DC transmission
c. From power stations, AC is produced so it is better to use AC then DC instead of converting it.
d. When a large fault occurs in a network, it is easier to interrupt in an AC system, as the sine wave current will naturally tend to zero at some point making the current easier to interrupt.

390Q. How can you relate power engineering with electrical engineering?

Power engineering is a sub division of electrical engineering. It deals with generation, transmission and distribution of energy in electrical form. Design of all power equipments also comes under power engineering. Power engineers may work on the design and maintenance of the power grid i.e. called on grid systems and they might work on off grid systems that are not connected to the system.

391Q. What are the various kind of cables used for transmission?

Cables, which are used for transmitting power, can be categorized in three forms:
• Low-tension cables, which can transmit voltage upto 1000 volts.
• High-tension cables can transmit voltage upto 23000 volts.
• Super tension cables can transmit voltage 66 kV to 132 kV.

392Q. Why back emf used for a dc motor? highlight its significance.

The induced emf developed when the rotating conductors of the armature between the poles of magnet, in a DC motor, cut the magnetic flux, opposes the current flowing through the conductor, when the armature rotates, is called back emf. Its value depends upon the speed of rotation of the armature conductors. In starting, the value of back emf is zero.

393Q. What is slip in an induction motor?

Slip can be defined as the difference between the flux speed (Ns) and the rotor speed (N). Speed of the rotor of an induction motor is always less than its synchronous speed. It is usually expressed as a percentage of synchronous speed (Ns) and represented by the symbol ‘S’.

394Q. Explain the application of storage batteries.

Storage batteries are used for various purposes, some of the applications are mentioned below:

• For the operation of protective devices and for emergency lighting at generating stations and substations.
• For starting, ignition and lighting of automobiles, aircrafts etc.
• For lighting on steam and diesel railways trains.
• As a supply power source in telephone exchange, laboratories and broad casting stations.
• For emergency lighting at hospitals, banks, rural areas where electricity supplies are not possible.

395Q  Write details of star distances ?

The common distance measures we use depend on what we are measuring.

1. For distances within our solar system, or other solar systems, the common unit is the 'Astronomical Unit' (A.U.)

1 A.U. = the average distance between the Earth and the Sun

2. For most everything else, stars, galaxies etc..., the distance unit is the parsec (pc). This is a convenient unit when measuring distances to stars by triangulation (what astronomers call parallax).

1 pc = 3.26 light years = about the distance to the nearest star

1 pc = 60 x 60 x 180/pi A.U. = 206265 A.U. --- by definition.

for distances within our galaxy or other galaxies it is kiloparsecs (kpc): 1 kpc = 1,000 pc

for distances between galaxies, and cosmology it is Megaparsecs (Mpc):

1 Mpc = 1,000,000 pc 3. The exception to these is when one is studying smaller object, such as a star or a planet. Then we might use kilometers. For dust grains, we might use microns (1/1,000,000 of a meter).

4. It is also common to compare objects. For example, if one is studying a star one might say "its radius is 5 solar radii", meaning it is 5 times the size of our sun. Similarly with galaxies, is it bigger or smaller than the Milky Way.