Category Archives: Science

Neon on the periodic table

Neon is a chemical element with the symbol Ne and atomic number 10. It is a noble gas, meaning that it is chemically inert and does not react with other elements. Neon is the fifth most abundant element in the universe, and it is the second most abundant noble gas in Earth’s atmosphere.

On the periodic table, neon is located in group 18 (or group VIIIA) and period 2. This means that it has 8 electrons in its valence shell, and it is a member of the noble gas family.

Neon has a very low melting point (-248.62°C) and a very low boiling point (-246.04°C). This means that it is a gas at room temperature. Neon is also a very light element, with a density of 0.9002 g/L.

Neon is a colorless, odorless, and tasteless gas. It is also non-flammable and non-toxic. Neon is often used in neon signs, because it glows a bright red-orange color when it is excited by electricity. Neon is also used in lasers and other electronic devices.

Here are some other interesting facts about neon:

  • Neon was discovered in 1898 by William Ramsay and Morris Travers.
  • The name “neon” comes from the Greek word “neos,” which means “new.”
  • Neon is the rarest of the noble gases in Earth’s atmosphere, making up only about 0.002% of the gas.
  • Neon is the second most abundant element in the Sun, after hydrogen.
  • Neon is used in a variety of applications, including neon signs, lasers, and electronic devices.

How many valence electrons does phosphorus have?

Phosphorus has 5 valence electrons. Valence electrons are the electrons in the outermost shell of an atom that are available to participate in chemical bonding. Phosphorus is in group 5A of the periodic table, which means that it has 5 valence electrons.

The electron configuration of phosphorus is [Ne]3s23p3. This means that the outermost shell of phosphorus has 2 electrons in the 3s orbital and 3 electrons in the 3p orbital. The 3p orbital can hold up to 6 electrons, so the 3 electrons in the 3p orbital are the valence electrons.

Phosphorus can form bonds with other atoms by sharing its valence electrons. For example, phosphorus can form a single bond with each of the 3 oxygen atoms in a molecule of phosphorus trioxide (P4O6). In this molecule, each phosphorus atom shares its 3 valence electrons with the 3 oxygen atoms, and each oxygen atom shares its 6 valence electrons with the 3 phosphorus atoms.

How to calculate the atomic mass?

There are two ways to calculate atomic mass:

  • By adding the number of protons and neutrons in an atom. The number of protons in an atom is its atomic number, and the number of neutrons is the difference between the mass number and the atomic number. For example, the atomic mass of carbon-12 is 12 because it has 6 protons and 6 neutrons.
  • By averaging the masses of the naturally occurring isotopes of an element. Isotopes are atoms of the same element that have different numbers of neutrons. For example, carbon has three naturally occurring isotopes: carbon-12, carbon-13, and carbon-14. The atomic mass of carbon is calculated by averaging the masses of these three isotopes, weighted by their natural abundance.

The formula for calculating the atomic mass of an element by averaging the masses of its isotopes is:

atomic mass = Σ(isotope abundance * isotope mass)


  • Σ means “sum of”
  • isotope abundance is the percentage of the element that is made up of that isotope
  • isotope mass is the mass of the isotope

For example, the atomic mass of carbon is calculated as follows:

atomic mass = (0.9893 * 12 amu) + (0.0107 * 13 amu) + (0.0000 * 14 amu)
= 12.011 amu

The atomic mass of an element is usually listed on the periodic table.

How to find an atomic number?

The atomic number of an element is the number of protons in the nucleus of an atom of that element. It is unique to each element and is always listed on the periodic table. The atomic number is also the same as the number of electrons in a neutral atom of that element.

There are a few ways to find the atomic number of an element:

  • Look up the element on the periodic table. The atomic number is always listed at the top of the element’s box on the periodic table.
  • Use a periodic table app or website. Many periodic table apps and websites allow you to search for elements by name or symbol. Once you have found the element, you can see its atomic number.
  • Calculate the atomic number from the mass number and number of neutrons. The mass number of an element is the total number of protons and neutrons in the nucleus of an atom of that element. The number of neutrons is the difference between the mass number and the atomic number. For example, the atomic number of carbon is 6 because it has 6 protons and 6 neutrons. The mass number of carbon is 12 because 6 + 6 = 12.

Here are some examples of how to find the atomic number of an element:

  • The atomic number of oxygen is 8.
  • The atomic number of hydrogen is 1.
  • The atomic number of carbon is 6.
  • The atomic number of gold is 79.

Petroleum Products Tnpsc

Petroleum Products

Petroleum products are a broad category of products derived from crude oil. Crude oil is a fossil fuel formed from the remains of ancient marine plants and animals that lived millions of years ago. It is extracted from underground reservoirs and undergoes various refining processes to produce different petroleum products.

Some common petroleum products include:

  1. Gasoline (Petrol): Gasoline is the most widely known petroleum product and is used as fuel for cars, motorcycles, and other vehicles. It is a volatile mixture of hydrocarbons that are refined to meet specific octane ratings.
  2. Diesel: Diesel fuel is used in diesel engines, commonly found in trucks, buses, trains, and some cars. It is a heavier, less refined product compared to gasoline and contains higher energy content.
  3. Jet Fuel: Jet fuel, also known as aviation turbine fuel (ATF), is used to power aircraft. It needs to meet strict specifications and performance requirements to ensure safe and efficient flight.
  4. Heating Oil: Heating oil is used for residential and commercial heating purposes, particularly in colder regions. It is similar to diesel fuel but with different additives to improve its performance in heating systems.
  5. Propane: Propane is a liquefied petroleum gas (LPG) commonly used for heating, cooking, and powering appliances like gas grills and generators. It is stored under pressure in tanks and can easily convert between gas and liquid states.
  6. Lubricants: Lubricants are used to reduce friction and wear between moving parts of machinery and engines. They include motor oils, hydraulic fluids, greases, and specialty lubricants for various applications.
  7. Petrochemicals: Petrochemicals are chemical compounds derived from petroleum products. They are used as raw materials in the manufacturing of plastics, polymers, synthetic fibers, fertilizers, detergents, and many other products.

Definition of atomic mass

The atomic mass of an atom is the average mass of all the isotopes of that element, taking into account their relative abundance. It is usually expressed in atomic mass units (amu).

The atomic mass considers the sum of the masses of protons, neutrons, and electrons in the atom. The atomic mass is crucial in chemical calculations, such as determining the mole-to-gram conversion or finding the percentage composition of elements in compounds.

The SI unit of mass is the kilogram, but atomic mass is often expressed in amu because it is a more convenient unit for measuring the masses of atoms.

The atomic mass of an element can vary slightly, depending on the isotopes of that element.

The atomic mass of an element is an important property of that element. It is used to calculate the mass of a mole of that element, and it is also used to determine the chemical properties of that element.


Properties of matter physical and chemical Tnpsc

Matter is anything that has mass and occupies space. It exists in various forms and can undergo physical and chemical changes. Here are the properties of matter based on physical and chemical characteristics:

Physical properties of matter:

  1. Mass: The amount of matter in an object.
  2. Volume: The amount of space occupied by an object.
  3. Density: The ratio of mass to volume.
  4. Color: The visual appearance of an object.
  5. Texture: The feel or consistency of a surface.
  6. Melting point: The temperature at which a solid turns into a liquid.
  7. Boiling point: The temperature at which a liquid turns into a gas.
  8. Solubility: The ability of a substance to dissolve in a solvent.
  9. Odor: The scent produced by a substance.
  10. Conductivity: The ability of a material to conduct heat or electricity.

Chemical properties of matter:

  1. Flammability: The ability to burn or react with oxygen.
  2. Reactivity: The tendency of a substance to undergo chemical changes.
  3. Acidity: The level of acidity or basicity of a substance.
  4. Toxicity: The harmful effects of a substance on living organisms.
  5. Corrosiveness: The ability to deteriorate or damage other materials.
  6. Oxidation: The process of combining with oxygen.
Basics of force in physics Tnpsc

Basics of force in physics Tnpsc


A body needs a ‘push’ or ‘pull’ to move or to bring a moving body to rest or change its velocity. Hence this push or pull is called force. Force has both magnitude and direction. Therefore force is a vector quantity.

Definition of force in physics

Types of Forces

Force is classified into types as:

  • Like parallel force – Two or more forces of equal or unequal magnitude acting along the same direction, parallel to each other.
  • Unlike parallel force – Two or more forces either equal or unequal forces act in opposite directions parallel to each other.

Unit of Force: SI unit of force is newton(N) and in the C.G.S system its unit is dyne.

Definition of 1 newton (N) – The amount of force required for a body of mass 1 kg to produce an acceleration of 1 kg⋅m/s2.

1 N = 1 kg m/s2


One dyne is the amount of force required for a body of mass 1 gram produces an acceleration of 1 cm/s-2.

1 dyne = 1 g cm/s-2 ; also 1 N = 105 dyne.

Unit Force

The amount of force required to produce an acceleration of 1 ms-2
in a body of mass 1 kg is called ‘unit force’.

Gravitational unit of force

The gravitational unit of force is kilogram-force, represented by kg f in SI units. In the C.G.S system, its unit is gram force, represented by gf.

1 kg f = 1 kg × 9.8 ms-2 = 9.8 N;
1 g f = 1 g × 980 ms-2 = 980 dyne

Issac Newton formulated three laws of motion.

  • Newtons 1st Law
  • Newtons 2nd Law
  • Newtons 3nd Law

These three are discussed later in the notes.


Mechanics is a branch of physics that studies the effect of force on bodies. It is divided into Statics and dynamics.

  • Static – Static deals with the bodies that deal with the bodies that are at rest under the action of force.
  • Dynamics – Dynamics deals with moving bodies under the action of forces. Dynamics is further divided into Kinematics and Kinetics
    • Kinematics – Kinematics studies the motion of bodies without considering the cause of movement.
    • Kinetics – Kinetics studies the motion of bodies considering the cause of movement.


When a force is applied to bodies, they resist change in their state. This property is called Inertia.

Example: We tend to move forward when the bus suddenly stops. Or We move backwards when the bike starts suddenly.

Inertia is defined as the interesting property of a body to resist the state of rest state of uniform motion unless it is influenced by an external unbalanced force.

Types of Inertia

  • Inertia of rest – The resistance of a body to change its state of rest is known as Inertia of rest.
  • Inertia of motion – The resistance of a body to change its state of motion is called Inertia of motion.
  • Inertia of direction – It is the resistance of a body to change its direction of motion is called Inertia of direction.

Linear Momentum

Linear momentum measures the impact of force on a body. The impact of a force is more when the velocity and the mass of the body are more.

The product of mass and velocity of a moving body provides the magnitude of linear momentum. It acts in the direction of the velocity of the object.

Linear Momentum = Mass x Velocity

That is: p = mv. It helps to measure the magnitude of a force.

The unit of momentum in the SI system is kg ms-1and in the C.G.S system, its unit is g cms-1.

Newton’s Laws of Motion

Newton’s First Law of Motion

This law states that “a body continues to be in its state of rest or state of motion along a straight line unless an external force at act on it”.

This gives the definition of force as well as inertia.

Newton’s Second Law of Motion

According to this law,” The force acting on a body is directly proportional to the rate of change of linear momentum of the body. And the change in momentum takes place in the direction of the force.”

This law is used to measure the amount of force. So this is also called as ‘law of force‘.

F = m x a

Force = mass x acceleration

Newton’s Third Law of Motion

This law states that ‘for every action, there is an equal and opposite reaction ‘.

Example: Recoil of Gun, Swiming, Birds flying etc.

Principal of Conservation of Linear Momentum

As per this principle, there is no change in the linear momentum of a system of bodies as long as no net external force acts on it.

Moment of Force

The rotating effect of a force about a fixed point or fixed axis is called the moment of the force about that point or torque (τ). Torque is a vector quantity and its SI unit is N m.

The torque is measured by-product of the force (F) and the perpendicular distance (d) between the fixed point or axis and the line of action of the force.

τ = F × d


When two equal and unlike parallel forces are applied simultaneously at two distinct points, is a couple.

The line of action of the two forces does not coincide and does not produce translator motion. This is because the resultant is zero. But a couple causes the rotation of the body.

This rotating effect of a couple is called the moment of a couple. The unit of the moment of the couple is Newton metre (N m) in the SI system and dyne cm in the C.G.S system.

Example: Turning of Tap, winding a Screw, Spinning of top

Moment of a couple = Force × perpendicular distance between the
line of action of forces

M = F x S


This article is for Tnpsc, for the topic ‘Force‘. This article provides a brief description of basic concepts of force in Physics. For detailed notes please refer to the Samacheer Kalvi book, Science 10th Std, Unit-1, Laws of Motion.

Halogen lamp working principle

How does a halogen lamp work?

A Halogen lamp is an incandescent lamp. It is also called Tungsten Halogen or quartz-halogen or quartz iodine lamp. It consists of a tungsten filament that is sealed in a transparent envelope. This envelope is filled with an inert gas mixture.

The inert gas mixture consists of a small amount of halogen i.e iodine or bromine. This halogen gas and tungsten filament produce a halogen cycle chemical reaction.

This chemical reaction redeposits the evaporated tungsten on the filament. This increases the life and maintains the clarity of the envelope. This process allows the filament operates at a higher temperature that a standard incandescent lamp.

Different types of battery cells and their uses

An electric cell converts chemical energy into electrical energy to produce electricity. It contains two electrodes immersed in an electrolyte called Anode and Cathode. A number of electric cells are connected together to form a battery.

When a cell or battery is connected to a circuit, electrons flow from the negative terminal to the positive terminal through the circuit. By using chemical reactions, a battery produces a potential difference across its terminals and this cell is called the Electrochemical cell

In an Electrochemical cell, the chemical energy is converted into electric energy and vice versa. This potential difference provides the energy to move the electrons through the circuit. The starting point to the electric cell is the experiment by Luigi Galvani and his wife Lucia on the dissected frog hung from the iron railing with brass hooks.

Primary cells are one in which the electric energy is derived by irreversible chemical action is called Primary cells.

Simple diagram for electric cell with electrodes, electrolyte solutions in a jar
Simple diagram for electric cell

Voltaic Cell

  • The simple cell or voltaic cell consists of two electrodes, one of copper and the other one is zinc dipped in dilute sulphuric acid in a glass vessel.
  • The anode is copper.
  • Cathode is zinc
  • The potential difference is 1.08 V
  • The electrolyte is dilute Sulfuric acid.

Daniel Cell

A simple diagram for Daniel cell, that  has two container with different electrodes and electrolytes connected by salt bridge
A simple diagram for Daniel cell
  • A galvanic cell example is Daniel Cell.
  • Invented in 1836 by John Frederic Danell.
  • It is a type of Galvanic cell or Voltaic Cell
  • The electrolyte is Copper Sulphate Solution in Copper Pot or Container dipped with a copper rod which acts as Cathode.
  • Zinc rod immersed in Zinc sulphate solution which acts as an Anode.
  • The two containers are connected by Salt Bridge which is a glass tube having potassium chloride or ammonium nitrate in a gelatin form.
  • Salt bridge allows ionic movement but prevents mixing
  • It cannot supply a steady current for a long time.

Leclanche Cell

  • It produces an Emf of 1.5 V and supplies current up to 0.25 A.
  • The anode is Carbon Rod.
  • The Cathode is Zinc Rod.
  • The electrolyte used is Ammonium Chloride.

Secondary Cells

  • The anode is lead.
  • The cathode is lead oxide.
  • The electrolyte is Sulphuric acid.
  • The advantage of a secondary cell is they are rechargeable.
  • The chemical process of obtaining current from a secondary cell is called Discharge.

Electromotive Force and Internal Resistance

The emf of a battery or cell is the voltage provided by the battery when no current flows in the external circuit. The electromotive force determines the amount of work a battery or cell does to move a certain amount of charge around the circuit.

It is denoted by Symbol ξ, pronounced as Xi. An Ideal battery has zero internal resistance and the potential difference across the battery is equal to its emf.

Practically, the battery is made of electrodes and electrolytes, there will be resistance to the flow of charge within the battery. This resistance is called Internal resistance r. For a real battery, the terminal voltage is not equal to the emf of the battery.

A brand new has low internal resistance and increases with aging.

Cell in Series

Several cells can be connected to form a battery. In a series connection, the negative terminal of one cell is connected to the positive terminal of the second cell. Then the negative terminal of the third cell and so on.

The free positive terminal of the first cell and the free negative terminal of the last cell becomes the terminal of the battery. Suppose n cells, each of emf ξ volts and internal resistance r ohms is connected in series with an external resistance R.

Series connection of cells is advantageous only when the effective internal resistance of the cells is negligibly small compared with R.

Cells in Parallel

In Parallel connection, all the positive terminals of the cells are connected to one point and all the negative terminals to a second point. These two points form the positive and negative terminals of the battery.

The current to the whole battery is the same for the connection of the Parallel cells. Hence it is advantageous to connect cells in parallel when the external resistance is very small compared to the internal resistance of the cells.

Domestic electric circuit explanation

The electricity generated from the power station is distributed to domestic and industrial users by overhead and underground cables. The first stage of the domestic circuit is to get the power supply to the main box from a distribution panel like a transformer.

The main components of the main box are the Fuse Box and Meter. The meter records the usage of electrical energy. The fuse box contains either fuse wire or MCB(Miniature Circuit Breaker)
The prime application of MCB or Fuse Wire is to protect the electrical appliances in the home from overloading due to excess current.

Mcb diagram: Mcb which is used for saving electrical devices in the time high voltage, electrical leakage etc
mcb diagram

An MCB is a switching device that can be activated automatically and manually. The MCB has a spring attached to the switch which is attracted by an electromagnet when an excess current passes through the circuit.

Thereby the circuit is broken and the protection of the appliance is ensured. The electricity is brought to the house by two insulated wires. One wire has red insulation called the live wire.
The other wire has black insulation called the neutral wire.

The alternating current of the electric potential of 220 V is supplied for domestic purposes. Both the live and neutral wires enter the box where the main fuse is connected with the live wire.

After the electricity meter, these wires enter into the main switch, which is used to discontinue the electricity supply whenever required.

After the main switch, these wires are connected to live wires of two separate circuits.
Out of these circuits, one circuit is of a 5A rating, which is used to run the electric appliances with a lower power rating, such as tube lights, bulbs, and fans.

The other one is a 15A rating, which is used to run electric appliances with a high power rating, such as air conditioners, refrigerators, electric iron, and heaters.

All the circuit is home is connected in parallel so that the disconnection of one circuit does not affect the other circuit.

Also, the parallel connection of circuits is that each electric appliance gets equal voltage.
In India domestic circuits are supplied with an alternating current of potential 220/230V and frequency 50Hz.

In countries like the USA and UK, an alternating current of potential 110/120V and frequency 60Hz is supplied.

Overloading and Short-Circuiting

The fuse wire or MCB will cut the circuit if there occurs overloading and short-circuiting. Overloading occurs when a large number of devices are connected in series to the same source of electric power.

This points to a flow of excess current in the electric circuit. If the quantity of current passing over a wire surpasses the highest allowable limit, the wires are heated to such a level that may cause a fire. This is called overloading.

When a live wire gets in touch with a neutral wire, it creates a short circuit. This occurs when the insulation or the packing of the wire gets degraded due to temperature variations and some other outside forces.

Due to the short circuit, the effective resistance in the circuit becomes very small, which starts the flow of a high current via the wires. This results in the heating of wires to such a level that a fire may be caused in the building.


A third wire called earth wire has a green covering or insulation connected to the body of the metallic electric appliance. Another end of the earth wire is connected to a metal tube or a metal electrode, which is buried into the ground.

This wire provides a low resistance path to the electric current. The earth wire conducts the current from the body of the electric device to the Earth, whenever a live wire unexpectedly touches the body of the metallic electric device.

Thus, the earth wire helps as a shielding conductor, which protects from electricity.

Consumption of electrical energy

Usage of Consumption of electricity is based on two factors: Amount of electric power duration of usage example 100 watt of electric power is used for 2 hours, then the power consumed is 100 x 2 = 200-watt hour.

Consumption of electrical energy is measured in Watt Hour, though its SI unit is watt-second.In practical terms, a larger unit is called kilowatt-hour (kWh). One kilowatt-hour is also called one unit of electrical energy.

One kilowatt-hour means an electrical power of 1000 watt used for one hour.Thereby, 1kWh = 1000 watt hour = 1000 x (60×60) watt second = 3.6 x 106 J.