HEAT

          Heat is the form of energy which produces in the sensation of warmth. It is responsible for the change in thermal condition of the body. Its SI unit is joule.

TEMPERATURE

          Temperature is a quantity that expresses the degree of hotness or coldness of a body.

Thermal Capacity

• Thermal or heat capacity of a body is defined as the amount of heat required to raise its temperature by 1K.

Its unit is joule / Kelvin (J/K or JK^-1)

Specific heat capacity (s)

• The amount of heat energy required to raise the temperature of 1 kg of substance through 1 K

Its unit is J kg^-1 K^-1

Change of state

• Solid and liquid states are the most predominant form of matter in our planet.
• That many substances change their state on supply or removal of heat energy.
• The process of converting a substance from one state to another is called change of state.

Melting

• The process in which a substance changes from the solid state into liquid state on heating is called melting or fusion.

Melting point

• The constant temperature at which a solid gets converted into its liquid state is called melting point.
• The melting point of ice is 0^o

Melting point of wax

• Solid without change of temperature. The melting point of wax is 57^o

Boiling

• The process in which a substance in its liquid state gets converted into vapor state is calling boiling.

Boiling point

• Arrange the apparatus as shown in figure.
• Take some water in boiling tube. Fix thermometer, so that its bulb remains just above the water level.
• The Boiling tube is heated. The mercury in the thermometer rises and remains constant at a temperature 100^o This constant temperature is called as boiling point of water.

Kelvin’s scale of Temperature

• There is a limit to the lowest temperature to which a substances can be cooled.
• The lowest possible temperature is taken as zero point of the Kelvin’s scale.
• This temperature is called as absolute zero. This is written as 0 K.
• At absolute zero there is no molecular motion and hence no heat energy in a substances.
• So absolute zero is the lowest temperature possible and denoted by 0 K or -273^o

Lord Kelvin

• He is widely known for his eminent contribution to thermodynamics.
• All objects at all temperature above absolute zero, emit thermal or heat energy.

Kelvin scale(K)=Celsius scale (^oC)+ 273

Celsius scale(^oC)=Kelvin scale (K) -273

Expansion of gases

• Robert Boyle is best known for his work in physics and chemistry. He formulated Boyle’s law. He is regarded as the first modern chemist.

Gas Laws & Gas Equation

Gas laws

• The expansion of gas is usually due to variation of pressure, volume and temperature.

Boyle’s law

• At constant temperature, the pressure of a given mass of gas is inversely proportional to its volume.
• It P is the pressure, V is the volume at constant temperature.

         pv = a constant

Charle’s law

• The relation between volume and temperature by keeping pressure constant, is called Charles law or law of Volume.
• Law of volume: At constant pressure, the volume (v) of a given mass of gas is directly proportional to its absolute temperature (T).

         = constant

Jacques Charles (1746-1823)

• He found the relation between the temperature and volume.
• He constructed the first hydrogen balloon, which brought him popular fame and royal patronage. He also invented hydrometer.

Gas equation:

Pv=RT

• Where R is proportional constant, and is known as gas constant.
• The value of R=8.31 J mol^-1 K^-1
• If n is the number of mole in the gas, pv=nRT
• If is the perfect gas equation .

Light Emitting Diode(Led)

• An electric bulb is used in the electric circuit to confirm the flow of current in the circuit However, the electric bulb may not glow if the electric current is weak.
• LED is light Emitting Diode, made up of semiconductor materials. A very small amount of current is sufficient to make and LED glow.

Applications of Chemical Effects of Electric Current

• Electroplating is the most common application of the chemical effects of electric current.

Electroplating

• What is electroplating?
• The process of depositing a thin layer of a metal on any conducting surface by the process of electrolysis is known as electroplating.
• In electroplating the meal to be coated is taken as cathode. The article to be coated is taken as anode and an appropriate solution is taken as the electrolyte.

Uses of Electroplating

• Electroplating is very useful and widely used in industries. For example chromium plating is employed on many objects like car parts, wheel rims, bath taps.
• Silver plating is used on tableware and electrical contacts; it has also been used on engine bearing.
• Zinc coated iron is called Galvanized from(GI). This iron is used in water taps (GI pipes), since they have high resistance to corrosion Using rubber gloves and shoes will protect us to a certain extent.
• The most extensive use of gold plating is on jewellery and watch cases. Zinc coating prevent the corrosion of steel articles, while nickel and chromium coated articles are used in automobiles and household appliances.

• The atom is made of 3 types of particles. They are (i) electron (ii)proton (iii) neutron.
• The electron is negatively charges, the proton is positively charged and the neutron has no charge, it is neutral.
• Atoms usually have equal number of positive and negative charges(protons and electrons)
• Hence an atom is electrically neutral. This is why most objects around us are electrically neutral.
• An atom is said to be electrically charged when the number of protons and the number of electrons is not equal.
• When the number of protons is higher then the number of electrons, the object is said to be positively charged.
• When the number of electrons is more than the number of protons, the object is said to be negatively charged.
• Hence charged objects can have either positive charge or negative charge.

Electroscope

• An electroscope is a device used to detect and measure electric charges.
• It works on the principle of Transfer of charges by conduction or induction.
• When a charged body comes into contact with a body which is not charged, the electric charges jump from the charged body to the uncharged body till the charges on the two bodies are equal. This process is called as discharging.
• Connecting a charged object to the earth with the help of conducting wires or physical contact is called as Earthing.
• The earth is considered to be huge reservoir of electrons. Depending upon the charge on the object, the earth provides or accepts electrons from a charged object connected to it.
• Many electrically operated devices in our homes(e.g .washing machines, refrigerator wet grinders etc.,) have earth connection.
• This is done so to save human handling them safety, and to save the appliances also

Story of Lightning and Thunder

• The enormous amount of heat produced during lightning causes the air to expand and vibrate suddenly, which is the causes of thunder.

Lightning –Safety

• Lightning is a high energy electric discharge. It strikes the earth with a lot of energy and heat.

Lightning arrester

• In order to protect tall building from lightning. Lightning arresters are used. It was invented by Benjamin Franklin.  It is a metal rod with pointed edges.
• It is fixed at the top of the buildings to be protected. This rod is connected to the ground with the help of a conducting table.
• The lower end of the cable is connected to a copper plate buried deep into the earth.
• Lightning strikes the rod and the electric charges are carried harmlessly to ground through the cable.

Transfer of Heat

• Heat always flows from a higher temperature to a lower temperature.
• There are three different ways in which heat is transferred from one body to the other.
• They are (i) Conduction (ii)convection    (iii)radiation

Conduction of heat

• Heat flows from one object the other when they are in contact with each other. For example a meal spoon left in hot water takes heat from the water and becomes hot.
• This method of transfer of heat from a body at a higher temperature to a body at a lower temperature when they are in direct contact is called thermal conduction.

Convection

• When fluids (liquid and gas) are heated the molecules closer to the source of heat get heated first and expand, thereby the density of the liquid decreases.
• The lighter molecules rise up and cooler and heavier molecules come down. This is called convection.

Radiation

• The sun is far away from earth and most of the space between the sun and the earth is empty. But still the warmth of the sun reaches the earth.
• The heat of the sun cannot reach us by conduction or convection as there are practically no molecules between the sun and earth to carry the heat through.
• The process by which heat is transferred without the help of any material or medium is called radiation.