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Putting the Shot and the Physics behind

Sot Put

Live Neutral Earth

Please help to find the answer of the following MCQ question. Thanks in advance

The cable to an electric cooker contains a live wire, a neutral wire and an earth wire.
When the cooker is working correctly, in which wires are the currents equal?

A – the live, the neutral and the earth
B – the live and the earth only
C – the neutral and the earth only
D – the neutral and the live only

Asked Sanka

Answer is D The Neutral and Live only

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When the appliance is switched on, the link is established between the live wire and neutral wire through the appliance and the same current flows through them

LIVE, NEUTRAL AND EARTH WIRE

Live wire:

A ‘live’ or ‘hot’ wire is a wire that is connected to a power source. This wire supplies voltage to a load (light bulb, hair dryer, etc.). When the load is also connected a neutral or another live wire this becomes a path for the flow of current (amps) known as a circuit.

Neutral

Neutral is return path for an AC circuit which is supposed to carry current in normal condition. This current may be because of many reasons, primarily because of phase current imbalance and some time because 3rd and 5th harmonics also.

There may be others reasons too but the magnitude of this current is in fraction of phase current and in few case it can be even double of phase current. So Neutral wire is always assumed to be charged (in active circuit). This neutral wire is given to ground (by grounding) to make the second terminal of neutral wire at zero potential.

Earth or Ground

Earth or Ground is for safety concerns against leakage or residual currents on the system via least resistance path. While phase and neutral is connected to main power wiring, earth may be connected to body of equipment or to any system which in normal condition doesn’t carry current but in case of some insulation failure, is supposed to carry some minor current.

This current is not directly coming from live or phase wire, but is from secondary links which was not in touch with live system in normal condition. This current is usually much lesser than main line current or phase current and mostly is in order of mA. But this leakage current is good enough to kill someone or may risk fire. Such current are being provided a low resistance path and sent to earth via earth wire.

Because of the difference in application we never mix grounding of neutral and earth. However both are made grounded (of-course the process may be different). If both will be mixed then the earth wire which is not supposed to carry any current in normal condition , may have some charges across and will become hazardous.

The circuitry in three phase system is a little different than single phase system.

Interestingly, neutral and earth are both grounded wires with one subtle difference, that is neutral is grounded where the transformer is located and earth is a local ground beside a house with an access to electricity.

Dr. Shashi Tharoor’s Inspirational Speech & Interactions At Sharjah International Book Fair

What is sound ? How does it travel?

What is sound ? How does it travel? (Asked Vivek Patel)

In physics, sound is a vibration that typically propagates as an audible wave of pressure, through a transmission medium such as a gas, liquid or solid.

Shashi Tharoor’s Inspirational speech in the United Nations

“neutron nucleus”

The picture of the atomic nucleus that we are given is that in order for the electrostatic repulsive force of the protons to be “neutralized”, neutrons are required to supply a measure of the “strong” nuclear force to overcome the electrostatic repulsive force. So, why can’t neutrons form their own associations independent of the need for protons? I know “free” neutrons are unstable and decay to protons and electrons, but the half life is about 10 minutes; seems to be plenty of time to form a “neutron nucleus”.

(DAVID KENNEDY posted this)

Answer

There are several issues here. If neutrons are together, They are not much different from free neutrons. The force of attraction between two neutrons will be that of gravitational force, which is so feeble and hence insufficient to hold the neutrons together to form a nucleus. If two neutrons are forced to be together, then one of the neutrons will transform to a proton emitting and electron and become a deuterium atom.

Forcing neutrons together will result in the creation of radioactive atoms.

Further references

https://www.sjsu.edu/faculty/watkins/neutronnucleus.htm

https://en.wikipedia.org/wiki/Neutron

Suresh Sir from S&G Institute responds:
If neutrons only are there in the nucleus, then, because they are neutral, the only force operating b/w them and atom will be gravity. It will be very weak and “neutron nucleus” cannot exist.
http://sandgscience.com/

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An independent neutron will split up into proton and electron, because, the splitting is energy feasible. (Mass of neutron is greater than the sum of masses of proton and electron.)
In case of proton – neutron pair, the splitting is not energy feasible. So neutron in pair with proton is more stable.

If a brass plate is inserted between the plates of a capacitor, what happens to the force between the two plates of the capacitor?

If a brass plate is inserted between the plates of a capacitor, what happens to the force between the two plates of the capacitor?

(Question received from FaceBook chat)

Answer:

The net force will decrease.

Image result for parallel plate capacitor with a metallic slab in between
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