NCERT NOTES

2021-06-21 16:41:52 Thomas Alva Edison

The person whose world-changing invention was the result of a 1000 times failures. The bulb was such a great invention that it bred numerous future inventions on its back.

When Edison was a child, his teachers called his parents regularly and tell them that their child is weak and can never succeed in life. His teachers were convinced that teaching a brain as slow as his, is a waste of time.

But no one knew that this person will invent so many things that people won’t forget him even after centuries! And the biggest learning of his success story were his 1000 attempts when he failed at his job. But he never stopped; his drive lead him to astonishing success and now he is one of the world’s most famous success stories.

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2021-06-20 16:48:22 ​​What is a Geiger Counter and How does it work?

A Geiger counter is a metal cylinder filled with low-pressure gas sealed in by a plastic or ceramic window at one end. Running down the center of the tube there's a thin metal wire made of tungsten. The wire is connected to a high, positive voltage so there's a strong electric field between it and the outside tube.

When radiation enters the tube, it causes ionization, splitting gas molecules into ions and electrons. The electrons, being negatively charged, are instantly attracted by the high-voltage positive wire and as they zoom through the tube collide with more gas molecules and produce further ionization.

The result is that lots of electrons suddenly arrive at the wire, producing a pulse of electricity that can be measured on a meter and (if the counter is connected to an amplifier and loud speaker) heard as a "click." The ions and electrons are quickly absorbed among the billions of gas molecules in the tube so the counter effectively resets itself in a fraction of a second, ready to detect more radiation. Geiger counters can detect alpha, beta, and gamma radiation. Open / Comment

2021-06-20 07:45:49 Open / Comment

2021-06-20 07:03:33 Open / Comment

2021-06-20 06:02:46 ​​How does Vacuum or Dewar Flask work?

A vacuum flask or a dewar flask works on the concept of insulation.

A vacuum flask or dewar flask is designed in a way to maximise insulation and limit heat transfer.

Most vacuum flasks have an inner glass chamber, a middle glass or stainless steel layer, and an outer plastic or metal casing.

A tight plastic stopper than can be screwed in or an airtight lid is also provided.

The inner glass chamber is lined with reflective layers and there is a vacuum separating the middle and the outer chambers.

The vacuum flask prevents all three modes of heat transfer by its design, the inner chamber is separated from the middle chamber with a vacuum, preventing convection and conduction, the mirrored layer within the inside chamber reflects any heat being radiated.
Since there is two degrees of separation between the inner and outer layer, there is no conduction.

For example, Let us say boiling water (100°c) is kept in an open vessel in a hotel at room temperature (15-20°c), due to the difference in temperatures, heat travels from the water to its surrounding, and hence the water cools down by losing heat to the environment.

However when the same water is stored in a vaccum flask or a dewars flask, heat transfer is inhibited hence keeping the water hot. Open / Comment

2021-06-19 11:13:11 Why does a magnetic compass point to the Geographic North Pole?

A magnetic compass does not point to the geographic north pole. A magnetic compass points to the earth's magnetic poles, which are not the same as earth's geographic poles.

Furthermore, the magnetic pole near earth's geographic north pole is actually the south magnetic pole. When it comes to magnets, opposites attract. This fact means that the north end of a magnet in a compass is attracted to the south magnetic pole, which lies close to the geographic north pole.

Magnetic field lines outside of a permanent magnet always run from the north magnetic pole to the south magnetic pole. Therefore, the magnetic field lines of the earth run from the southern geographic hemisphere towards the northern geographic hemisphere. Open / Comment

2021-06-17 16:57:53 SCIENTIFIC INSTRUMENTS

Altimeter:- Measures altitudes.

Ammeter:- Measures electric current.

Anemometer:- Measures force and velocity of wind and directions.

Audiometer:- Measures intensity of sound.

Barograph:- Continuous recording of atmospheric pressure.

Barometer:- Measures atmospheric pressure.

Binoculars:- To view distant objects.

Bolometer:- To measure heat radiation.

Callipers:- Measure inner & outer diameters of bodies

Calorimeter:- Measures quantities of heat

Cathetometer:- Determine heights, measurements of levels, etc. in scientific experiments.

Chronometer:- Determines longitude of a vessel at sea

Colorimeter:- Compares intensity of colours.

Commutator:- To change the direction of electrica current.

Cryometer:- A type of thermometer used to measure very low temperature, usually close to 0° C.

Dilatometer:- Measures changes in volume substance.

Dynamo:- Converts mechanical energy into electrical energy.

Dynamometer:- Measures electrical power. Open / Comment

2021-06-17 10:47:51 Results will be declare on 31st of July... We ready guys!! Open / Comment

2021-06-17 10:10:44 Open / Comment

2021-06-17 10:10:44 Why Do Athletes Have a Lower Heart Rate?

Increased cardiovascular fitness causes real physical changes in the structure of the heart. The muscles in the heart wall thicken, and the heart pumps more blood with each beat. That increased efficiency means an athlete's resting heart rate falls to a level that could indicate trouble in a nonathlete. Many athletes don't realize that high levels of conditioning also cause heart symptoms that doctors might mistake for serious problems. During exercise, the untrained heart beats faster, but not as efficiently as in trained athletes. Output during maximum exertion increases to 14 to 20 liters per minute, far below the 40 liters per minute of an elite athlete.

The resting heartbeat of an athlete can fall below 40 beats per minute. When you exercise, your heart works harder when other muscles in the body pump more blood back to the heart. The major muscles of the legs have large veins that fill during the relaxation stage of the movement, and the muscle contraction in the active movement pushes the blood back into the circulatory system. Increasing blood flow triggers a faster heartbeat. Because the heart muscle of conditioned athletes enlarges and strengthens, the hearts of athletes pump more blood per beat. An athlete's maximum heart rate, as well as resting heart rate, falls below the pace of the average heartbeat.

Conditioning causes physical and electrical changes in the heart, creating a beneficial condition called "athlete's heart." Aerobic training, such as running or swimming, causes your heart to develop larger heart chambers. Participants in anaerobic sports, such as weightlifting, increase the thickness and strength of their heart muscles. Mixing the two types of training creates both types of heart improvement. During intense exercise, the hearts of highly trained athletes pump as much as twice the volume of blood as the hearts of untrained people. Open / Comment