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.