HEAT

    Heat:-

Heat is a form of energy (heat energy/thermal energy), that is transferred from one body to another, due to the existence of a temperature difference between them.

Transfer of heat energy/thermal energy always takes place from the body at a higher temperature to that at a lower temperature.

•  HEAT AND TEMPERATURE :-

We often observe that when we hear a body, it's temperature rises. This indicates that heat and temperature are related to each other. Heat is the energy of a body that is due to the motion of its constitution particles (molecules). Temperature, on the other hand, is just ab indicator of this energy. Even a cold object possesses heat energy due to the motion of its particles (molecules). When we add, (or remove) heat (from) a body, motion of its molecules becomes faster (or slower).

• EFFECT OF HEAT :-

When a body is heater, various types of physical and chemical changes are observed to take place. We list below some of the main effect of year.

    ● PHYSICAL CHANGES :-

       (a) Change in temperature: We all know that addition, or removal, of heat to, or from, a body brings about a change in its temperature. Addition of heart to a body (usually) raises its temperature, whereas, removal of heat , from a body (usually), lowers is temperature.

    (b) Change of state: Under appropriate conditions, addition, or removal, of heat to, or from, a body, can also bring about a change in its state. For example, on putting a tray of water (liquid form) in the freezer compartment of a refrigerator, the water freezes to form ice. Ice, as we know, is the solid form of water. Similarly, when water is heated over a flame, it starts boiling and gets converted into steam. Steam, as we know, is the gaseous or vapour form of water.

     (c) Thermal expansion: Most of solids, liquid and gases, are known to expand on hearing. This phenomenon is called thermal expansion. For example, the metal rim, to be put on a cart wheel, is designed to have a(slightly) smaller diameter than that of the wheel. When this rim is heated, it becomes 'red-hot', expands, and slips on to the wheel easily. When it is cooled, it contacts and grips the wheel firmly.

   ◆ CHEMICAL CHANGES:-

  Many chemical changes take place only when the reactants are heated up. For example, we can prepare oxygen, in the laboratory, by hearing potassium chlorate (along with manganese oxide as a catalyst) over a flame.

• Thermometer:-

A more reliable method to know the relative hotness or coldness, I.e. the temperature of a given body. We use special instruments fir this purpose. All such instruments, or devices, are known as thermometers.

It is based on the thermal expansion of mercury.

It consist of a narrow capillary tube of glass that is closed at its upper end and has a bulb at its lower end. The bulb is filled with mercury. Inside the capillary tube we can see a small shining thread of mercury. The mercury, present in the bulb of the thermometer, expands when heated. The extent of its expansion, and, therefore, the length of murcury thread in the capillary tube, depends on the extent of hearing of the thermometer. This, in turn, depends on the temperature of the object with which the thermometer bulb has been put in contact. The length of the mercury thread (in the thermometer) can, this, give us a measure of the temperature of the object.

◆Two scales, that have been in common use, are the Fahrenheit and the Celsius.

【the temperature 'T' in degree Celsius (°C) is equal to the temperature 'T' in degree Fahrenheit (°F) minus 32, times 5/9. 】

           T (°C) = [T (°F) - 32] × 5/9

◆The range of a laboratory thermometer can be from -10°C to 110°C and 0°C to 100°C are found more often in school laboratories.

Transfer of heat:-

● Conduction 

In this method, heat is transferred from one particle (molecule), of the object, to the next, and then to the next, and so on, without the particles leaving their places. The particles just vibrate about their mean position, and keep on passing heat energy, to their 'next-in-line' neighbours.

● Convection

The molecule in liquids (and gases), are quite free to move. This is unlike solids whose molecule are quite rigidly fixed. It is this ability of liquid molecules (to move around) that causes a liquid to get heated up. We can this method of heart transfer, in liquid (and gases), as convection.

◆ Land and Sea Breezes:-

Water gets heated up slowly than karne during day time. Hence, the air above the land gets heater up more quickly and rises up. Cooler air, from above the sea, then rushes in to take it's place. We call this movimiento of air as a Sea Breeze.

During night, water cooled more slowly than land. The air, above the water, therefore, because warmer and rises up. It's place is taken up by the cooler air above the land. This movement of air is called as Land Breeze.

◆Radiation

It may be defined as a method of heat transfer in which no material medium is required. The heat energy, received by an object through radiation, is called radiant energy. We say that all hot objects give out, or radiate, heat energy.

Magnetic property of matter

                 MAGNETIC PROPERTIES OF MATTER

INTENSITY OF MAGNETIZATION: -

If a magnetic material (ferromagnetic substance) be kept in magnetic field, the material get magnetized and a magnetic moment get induced. The magnetic moment so induced per unit volume is called intensity of magnetization

                                                                           

                         

               H – Magnetizing field (external field)

M = m × 2l

Volume of the material = A ×  2l

Intensity of magnetization, I = M/volume = m/A

MAGNETIC SUSCEPTIBLITY: -

The magnetic susceptibility refers the ability of the material that to what extent the material can be magnetized by using magnetizing field. If constant magnetic field be given to two different material, the material having the greater susceptibility will have the greater magnetization.

                                                              It is observed that the intensity of magnetization depends directly on the magnetizing field.

                                     I ∞ H

                                Or, I =  ꭙH

 Where, ꭙ is the magnetic susceptibility.

MAGNETIC INDUCTION: -

If a magnetic material be kept in magnetizing field, magnetic moment gets induced and certain magnetic line of the force will pass through the material. The magnetic induction is the total no. of magnetic line of force passes through the material per unit area.

H – given magnetic field intensity

GAUSS’s Law of Magnetization says that 4π lines are associated with unit pole strength.

                              B = H + 4πm/A (for Ferro or Para)

                                  = H + 4πI

                          B = H -  4πm/A ( for Dia)

                                  = H - 4πI

Magnetic permeability: -

It is the ratio of magnetic line of force when a specimen be kept in magnetizing field to the no. of line of force when there is no material

                             µ = B/H

                         MAGNETIC MATERIALS

1)     DIAMAGNETIC SUBSTANCE: -

These substances are repelled by magnet, atoms possess paired electrons.

PROPERTY

A)     If a diamagnetic substance be kept in non-uniform magnetic field, it moves from the region of strong magnetic field to the region of weak magnetic field.

                     Potential Energy of a magnetic dipole 

                   U = MBCosθ

Angle between M and B i.e. θ = 180

                   U = MB

Every body try to be posses minimum P.E.

So B should be minimum

    A)     The susceptibility is -ve.

    B)     Magnetic permeability is less than one.

    C)      The Diamagnetic substance losses its magnetic property immediately after removing the field.

    D)     The magnetic property of diamagnetic substances is independent of temperature.

B)    PARAMAGNETIC SUBSTANCE: -

Thee substances are attracted by magnet but very feebly. The atoms possess unpaired electrons.

PROPERTIES

a)  If a paramagnetic substance be kept in non – uniform magnetic fields, it moves from the region of weak magnetic field to the region of strong magnetic field.

P.E. of a magnetic dipole,

                             U = - MBCosθ

                           Angle between M and B i.e. θ = 0

                     U = - MB

                  Every body try to be possess minimum P.E.

                 So, B should be maximum.

                 

b)      The susceptibility is +ve.

c)      Magnetic permeability is greater than one.

d)      The Paramagnetic substance losses its magnetic property immediately after removing the field.

e)      The magnetic property of diamagnetic substances is independent of temperature.

                                I ∞ 1/T

B)    FERROMAGNETIC SUBSTACE: -

These Substances are strongly attracted by magnet. Some of the paramagnetic substances which having strong magnetism are separately called Ferromagnetic substances because ferrum is the strongest of all Iron, Nickel, Cobalt, Gadalinium, Dysposium are the Ferromagnetic substance

PROPERTIES

a)       If a ferromagnetic substance be kept in non – uniform magnetic fields, it moves from the region of weak magnetic field to the region of strong magnetic field.

P.E. of a magnetic dipole,

                                                        U = - MBCosθ

                           Angle between M and B i.e. θ = 0

                                                   U = - MB

                  Every body try to be possess minimum P.E.

                 So, B should be maximum.

           

b)      The susceptibility is more +ve.

c)      Magnetic permeability is much greater than one.

d)  The ferromagnetic substance does not losses its magnetic property immediately after removing the field.

e)      The magnetic property of diamagnetic substances is independent of temperature.

                                               I ∞ 1/T

            2) A CURRENT CARRYING LOOP BEHAVES AS A MAGNETIC DIPOLE: -

                If a bar magnet be kept in magnetic field, torque acts on the magnet is

                                                       Ⴀ = MBSin θ……………………………………….(1)

                Similarly, if a current carrying loop be kept in magnetic field, Torque act on it is-

                                                       Ⴀ = BIASin θ……………………………………….(2)

   

                  

                   Comparing (1) and (2), we get

                               Magnetic Moment, M = IA

                                               = Current × Area

Let an electron revolve in an orbit of radius ‘r’ with velocity v

                                                                         M = I × A

But              v = r ω

i.e.                 ω = v/r

        M = e v r/2

                 Multiplying and dividing by ‘m’

                    

                  Where L = m v r is called angular momentum

                   

From Bohr’s theory of stationary non – radiation orbit

  mvr(L) = nh/2π

 M = e × nh/2πm

      = n (eh/4πm)

  

                                                                   If n = 1 (Least value)

                                                               (Bohr’s magneton)

Motion

Motion:- We called an object to be in motion when its position changes with time.

Example:- Moving vehicles, flying Birds,  Riding Bicycles Etc.

Rest:-  Any motionless object is said to be at  rest.
                          -:Types of Motion:-

1) Motion in a straight line is called rectilinear motion.
Example:- Book on the table.

Example:- Moving car in a straight path.

2) In circular motion an object moves such that its distance from a fixed point remains the same.

Example:- The motion of a point marked on the blade of an electric fan or the hands of a clock are examples of circular motion

3) Motion that repeats itself after some period of time is called periodic motion.

Example:- A branch of a tree moving to and fro, motion of a child on a swing

Speed:-

We call the distance covered by an object in a unit time as the  speed  of the object.

So, for us the  speed is the total distance covered divided by the total time taken. 

Thus,

             Speed  =  Total distance covered  
                                   Total time taken

                             (Unit of speed is m/s )

In everyday life we seldom find objects moving with a constant speed over long distances or for long durations of time. If the speed of an object moving along a straight line keeps changing, its motion is said to be  non-uniform. On the other hand, an object moving along a straight line with a constant speed is said to be in  uniform motion. In this case, the average speed is the same as the actual speed.