Why do we have 10-digit mobile numbers? This is probably something most of us do not really think about. But it has a very sound logic to it. 

The logic: The number of digits in a mobile phone number decide the maximum mobile phones we can have without dialing the country code, ie. 91 (for India). To understand this we need to go back to school. Remember permutations & combinations. Suppose I had a pair of jeans (J1-2) and four tee-shirts (T1-4). The possible combinations are: J1T1, J1T2, J1T3, J1T4, J2T1, J2T2, J2T3, and J2T4, ie. 8 combinations {2 (no. of jeans) X 4 (no. of tee-shirts)}.

The same logic is used when computing the digits in a mobile phone number or for that any numbers such as those for vehicles, land-line telephone numbers, etc. Now suppose if we had a 6-digit cell number, the maximum number of unique cell numbers possible would have been (10 x 10 x 10 x 10 x 10 x 10), ie. a maximum of 1,000,000 subscribers. We have already crossed the 100-million mark in India. So obviously we could not have had a 6-digit cell phone number. Not even a 7-digit because that would've resulted in a capacity of 10 million, not even 8-digit (100 million subscribers), and not even a 9-digit (ie. 1000 million or 100 crore, since our population is close to 125 crore and growing).

A 10-digit cell number offers us a capacity to have 10 billion (1000 crore) subscribers, which is far more than what our country can even achieve. We are v.v.v.unlikely to have a population or a subscriber base of 1000 crore but there is a remote likelihood of us having 100 crore subscribers. Hence, a 10-digit mobile phone number.


1.)ANEMOMETER – An instrument for measuring the velocity of flow of a gas, either by mechanical or electrical methods.

2.)ATMOSPHERIC PRESSURE – The force exerted by the weight of the atmosphere on every point with which it is in contact.

3.)ECCENTRIC AND STRAP – An eccentric is a disc having its axis of rotation
out of its centre. It is equivalent to a crankpin which is so large in diameter
that embraces the shaft to which it is attached and dispenses with arms.
Converts rotary motion into reciprocating motion.

4.)EFFICIENCY – Ratio of the useful work performed by a prime mover to the energy expended, that is, the output divided by the input.

5.)ENBLOCK CYLINDERS – Two or more cylinders cast integral, that is all in one casting.

6.)FEATHER VALVE – A valve which consists of a strip of ribbon steel which covers a slightly narrower slot when the value is closed.

7.)FINGER VALVES – Valves consist of narrow strips of stainless. fastened to the seat at one end and free to flex along their length. Suitable for light service.

8.)MULTISTAGE COMPRESSION – Dividing the compression of air into two or more stages so as to obtain the work saving due to a nearer approach to isothermal compression by using intercooling.

9.)PISTON SPEED – The total distance travelled by the piston in one minute, not the actual velocity at any given instant.

10.)PORTABLE COMPRESSOR – A small compressor which is easily moved from place to place


Back in 2013, modern-day Iron Man Elon Musk unveiled his concept for a high-speed transportation system he described as a cross between a Concorde, a railgun, and an air hockey table. Dubbed the "Hyperloop," this futuristic train would theoretically be capable of catapulting passengers at supersonic speeds, up above ground, inside giant tubes. It seemed a little pie-in-the-sky then, and it's still widely misunderstood, so we checked in to see how much progress has been made, and how close we are to ping-ponging cross-country in a flash.

1. It will travel at 800mph

As outlined, the Hyperloop would be capable of traveling faster than the speed of sound. To put that in perspective, a trip on the Hyperloop from LA to SF -- the route initially proposed by Musk -- would take just 35 minutes, compared to a six-hour drive, or hour-plus commercial flight. 
2. The passenger pods float inside giant steel tubes using magnetic pressure. You know those pneumatic tubes at the bank drive-up window that you use to shoot the teller your deposit slip? Imagine that, but big enough to fit a couple dozen passengers, and you've got the right idea. Musk's plan involves using magnets to propel aerodynamic capsules (where the people will sit) through giant steel tubes, sidestepping any friction by keeping it afloat on a constant pressurized cushion of air. 
3. Actual pod concepts will be competing on a Hyperloop test track this year
Based on Elon Musk’s track record, you’d be silly to underestimate him. However, it’s pretty wild how close we are to seeing a real, live Hyperloop in action. Just last month, Musk’s aerospace company SpaceX hosted a competition of 120 teams of high school and college students, challenging them to come up with innovative Hyperloop pod designs (MIT took the top spot, by the way). Additionally, the construction of test tracks in California and Nevada is underway, where the students will test their pod designs later this year.

4. It's self-powering

One of the biggest draws for a Hyperloop, besides speed of course, is that it would be eco-friendly and self-sustaining. The design, as outlined by Musk, involves topping the steel tubes with solar panels, which store the energy that powers the air compressors that cushion the pods, as well as other vital components. Enough energy would be stored so that even at night or in cloudy weather the Hyperloop could continue operating normally.

5. It could only run in a fixed straight line, or else the speed would make you sick

Humans can only handle about 0.2 Gs of acceleration up and down or side to sidewithout turning into walking, talking vomit machines. So essentially, if this thing is rocketing at 800 miles per hour, it will be crucial that it travel along a straight fixed plane. No tubes could go down into valleys or up and across mountains; that means carving a lot of tunnels and constructing giant pylons, which would be hugely expensive. And even under the optimal conditions, moving about the cabin would be incredibly dangerous, especially if it needed to suddenly slow down.
6. Minor malfunctions would be catastrophic When you’re catapulting inside a windowless vacuum at supersonic speeds, even the slightest disruption to the air around it is game over. There would be airplane-style oxygen masks that drop down in the event of a loss of pressure inside the pod, but what about an unexpected jolt from outside the tube (an earthquake, freak explosion, etc.) that cracks the facade? Or what if any of the air compressors that cushion the pod fail? Either of those scenario ends with an out-of-control, train-sized bullet violently bouncing off the walls. That would be bad.

7. It will cost less than you think

According to Musk and others, the Hyperloop route between LA and San Francisco would cost roughly $6 billion to build, which is nearly one-tenth the overall cost of the high speed rail service California has planned. When you put that in perspective with the Hyperloop’s 35-minute one-way trips (compared to the high speed rail’s 180 minute predicted trip time), it sounds like an even more attractive plan. 


Have you ever imagined the state of our lives without this smart and most-demanded invention of the wheel? Sheer misery and the life of caves and hunting. The earliest of humans invented it to their greatest convenience, and gears came thousands of years later. This little invention is as old as 27th Century B.C., but now it continues to be an essential part of nearly every piece of machinery we lay our hands on.
Have you ever considered how these disks of gear wheels are made? Also, how those little details and the intricate and fine teeth on the gear wheels are always perfect and precise? It is not as simple as it might sound, and as painstaking as the process might be, it is an absolute treat to watch.
This video might force you to put in more thoughts into the details of the things that we use in our daily lives.


1) Important Air Conditioner Terms

SEER: Seasonal Energy Efficiency Ratio. Just remember this, higher the SEER, more will be the efficiency of unit, resulting in a lower operating cost.
Blower (Blower Motor): The motor and fan assembly mounted near the evaporator that draws air over the evaporator. In automotive applications, the blower motor may draw outside or inside air, depending on control settings.
Charging: Adding refrigerant to a system.
Flushing: A process of cleaning the internal components of an A/C system. This process requires the removal of refrigerant. This process is used to remove contamination and corrosion from the system.
Compressor: The pump that moves the refrigerant from the indoor evaporator to the outdoor condenser and back to the evaporator again.
Refrigerant Oil: Highly refined oil that is free of contaminants. Used in the A/C system for the sole purpose of maintaining compressor lubrication.
Ductwork: A pipe or conduit through which air is supplied.
Evaporator coil: It is the network of tubes that are filled with refrigerant. It is located inside the home within the indoor unit and takes heat and moisture out of the indoor air when liquid refrigerant evaporates.
2) How Air Conditioner Works?
Air conditioners use the basic refrigeration process to cool indoor air. However, conditioning is different from refrigeration as it also regulates air humidity, quality, and speed besides the temperature. When a liquid (refrigerant) converts into gas, it absorbs heat, and this is called evaporation or phase conversion. This occurs in the evaporator part of the system. Whereas, when the refrigerant is condensed, it turns back into liquid, and this happens in the condenser. Other key components include expansion valve, compressor, and the collector. Air conditioners use phase conversion by forcing refrigerants to evaporate and condense in a closed system of coils repeatedly.

3) Purpose Of Air Conditioner Filters

Filters remove particles from the air to keep the dust out of your car AC’s air ducts. Make sure you change your ‘dirt air filter’ every 1-3 months depending on your surroundings and usage. Not changing your air filters can bring problems like dirty air, reduced airflow, increased fuel consumption, low quality of cooling, and frozen coils.

4) Maintenance Of Air Conditioner

Your air conditioner becomes less efficient, weak, and unreliable when it is not taken care of. This will cause headaches for you and probably increase repair bills in case you ignore it up to the point of busting it.
Just like the rest of your car, your air conditioner needs regular service. If the air conditioner is not running properly, it may be working too hard. This could result in inconsistent air temperatures, heating of the car, and reduced comfort.
If you need more convincing, most manufacturers require routine maintenance for their warranty on the air conditioners to remain valid. So go get your car AC checked up in case you feel it is not working up to the mark.

5) Importance Of Air Ducts

It is important to have your car’s air ducts cleaned and checked for leaks. Sometimes dust or leaves get stuck up in the air ducts, wrecking havoc with your cooling system and the blower. A clean air duct system will help your car AC last longer by removing contaminants that decrease your system’s efficiency and consume more fuel.

6) Increasing Air Conditioner Efficiency

Keeping your air conditioner maintained and tip top is the best thing you can do for its performance and your wallet as well. Sealing leaky ducts, keeping the right refrigerant charge, increasing your thermostat by a few degrees, replacing filters, cleaning coils, using car window tinting, parking in the shadow, insulating the air ducts are all great ways that help to increase the energy efficiency of air conditioner.


Indian Railways, which is operated by Government of India under the Ministry of Railways, is solely responsible for the rail transport in the country. It is considered as the fourth largest railway network in the world, with a running track of 92,081 km and covers a distance of 66,687 km. Indian Railways has carried 8.107 Billion passengers in 2015-16 alone.

That is approximately 22 Million passengers a day. In order to make the rail travel comfortable, 7216 stations are built in different parts of the country. There is a difference in the names of stations, like some are named Junction, some as Terminus and some are named Central. So, have you ever wondered what is the difference between a Junction, Terminus, Central and a Railway Station?

Here’s the answer:

Railway stations are mainly differentiated into 4 types.

1. Terminus

A station is known as a Terminus/Terminal when the trains can enter and leave the station in only one direction. In other words, the track ends in the other direction. A train has to leave in the same direction as it entered. Some examples of Terminus are:Chatrapati Shivaji Terminus (CST),Lokmanya Tilak Terminus (LTT)

2. Central

A Central is a busiest and most important station in a city, which has multiple stations. It deals with a large number of arrivals and departures. These may be the oldest stations, so they are named as central. It is not necessary to have a Central if a city has multiple stations. There are 5 Central stations in India:Mumbai Central (BCT),Chennai Central (MAS),Trivandrum Central (TVC),Mangalore Central (MAQ),Kanpur Central (CNB)

3. Junction

If there are at least 3 different routes coming in and going out of a station, then it is called a Junction. In simpler words, trains entering the station should have at least 2 different routes to leave the station.Some examples of Junction are:Mathura Junction (7 routes),Salem Junction (6 routes),Vijayawada Junction (5 routes),Bareilly Junction (5 routes)

4. Station

A station is simply a place where a train stops for passengers/goods to enter and leave the train.
Note: Chennai Central can also be called as Terminus but as it is one of the oldest stations in India, it is being continued as Central. Same applies to other stations also.


Common types of cross-sections for irrigation canals are trapezoid, parabolic, triangular, circular, and irregular (natural). Square / rectangular cross sections are used normally for concrete ducts.Out of these trapezoidal cross section is widely used due to following reasons :-

1)Heavy rains - The trapezoid has its width gradually increasing towards the top. In case of heavy rains , since the water level increases ,the trapezoid geometry ensures that the channel doesn’t overflow as the water is accomodated in the larger areas at the top of the trapezoid.

2) Velocity - The ratio of flow area to the contact area with the wall is very high. This decreases the effect of viscous forces on the flow velocity of water,thus making it move faster.

3) Safety - If someone or something falls into the canal by mistake, it is easier to climb a wall with a gradual gradient like the trapezoid unlike a vertical wall.

4.)Discharge-The best thing about a trapezoidal channel is that it has maximum discharge i.e., maximum volume of water flows through it within 1 second, when compared to rectangular, circular and triangular channels.

5.)This trapezoidal section offers least frictional resistance. 

6.)It is easy to maintain such as dredging and tile work in trapezoidal canal can be done by even unskilled labour and less equipments.