- molecule of gas moves all direction with all possible velocity during motion,the molecules colloid with one another but the collision do not effect the molecular density of gases
- The motion of molecules is random(the center of mass f gas remain at rest)
- Between two collisiona molecules move in straight line with uniform velocity this is because no force act on the particle b/w the collision.The distance covered by molecules is called mean free path
- The diamension of the molecules may be neglected as compared to the dimension of free path.
- No approciable force of attraction or repulsion by molecule on in another accept during collision
- Collision between melecules and with the wall of the container or perfectlly elastic and the time of impact is of neglagible duration (elastic collision means no change of linear momentum and kenetic energy ) elastic collision means no change of momentum but energy change
- Molecules obey newtons law of motion
Different Assumption made in the study of kenetic theory of gases
Conversion of galvanometer into a voltmeter
Voltmeter is an instrument used to measure potential difference between the two ends of a current carrying conductor.
A galvanometer can be converted into a voltmeter by connecting a high resistance in series with it. The scale is calibrated in volt. The value of the resistance connected in series decides the range of the voltmeter. Galvanometer resistance = G
The current required to produce full scale deflection in the galvanometer = Ig
Range of voltmeter = V
Resistance to be connected in series = R
Since R is connected in series with the galvanometer, the current through the galvanometer,
Ig = V/(R + G)
∴R = (V/Ig )– G
From the equation the resistance to be connected in series with the galvanometer is calculated.
The effective resistance of the voltmeter is
Rv = G + R
Rv is very large, and hence a voltmeter is connected in parallel in a circuit as it draws the least current from the circuit.
The resistance of the voltmeter should be very large compared to the resistance across which the voltmeter is connected to measure the potential difference. Otherwise, the voltmeter will draw a large current from the circuit and hence the current through the remaining part of the circuit decreases. In such a case the potential difference measured by the voltmeter is very much less than the actual potential difference.The error is eliminated only when the voltmeter has a high resistance.
An ideal voltmeter is one which has infinite resistance
A galvanometer can be converted into a voltmeter by connecting a high resistance in series with it. The scale is calibrated in volt. The value of the resistance connected in series decides the range of the voltmeter. Galvanometer resistance = GThe current required to produce full scale deflection in the galvanometer = Ig
Range of voltmeter = V
Resistance to be connected in series = R
Since R is connected in series with the galvanometer, the current through the galvanometer,
Ig = V/(R + G)
∴R = (V/Ig )– G
From the equation the resistance to be connected in series with the galvanometer is calculated.
The effective resistance of the voltmeter is
Rv = G + R
Rv is very large, and hence a voltmeter is connected in parallel in a circuit as it draws the least current from the circuit.
The resistance of the voltmeter should be very large compared to the resistance across which the voltmeter is connected to measure the potential difference. Otherwise, the voltmeter will draw a large current from the circuit and hence the current through the remaining part of the circuit decreases. In such a case the potential difference measured by the voltmeter is very much less than the actual potential difference.The error is eliminated only when the voltmeter has a high resistance.
An ideal voltmeter is one which has infinite resistance
Definition of few Important quantities Thermal Equilibrium, Specific Heat, Water equivalent
Thermal Equilibrium
When two body is in contact and there is no transfer of heat between two body then bodies said to be in thermal equilibrium
Specific Heat
The amount of heat required to increase the temperature of unit mass of the substance by 1 degree centigrade is called specific Heat
Thermal capacity
it is defined as the amount of heat energy required to increase its temperature through 1 degree centigrade.
Its S.I unit is Joule/kelvin
Latent Heat
The heat energy released or absorbed at constant temperature per unit mass for change of state is called latent Heat.
Q = mL
L= latent heat
m= mass of substance
Water equivalent
It is the quantity of water whose thermal capacity is same as the heat capacity of body . it is denoted by W
W= ms
Hoar Frost
The conversion of solid into vapour state is called hoar frost
Sublimation
The direct conversion of solid into vapour state is called Sublimation.
Boiling point
It is the temperature at which liquid get boils is called boiling point
Melting Point
Conversion of solid into liquid at constant temperature is called Melting .
When two body is in contact and there is no transfer of heat between two body then bodies said to be in thermal equilibrium
Specific Heat
The amount of heat required to increase the temperature of unit mass of the substance by 1 degree centigrade is called specific Heat
Thermal capacity
it is defined as the amount of heat energy required to increase its temperature through 1 degree centigrade.
Its S.I unit is Joule/kelvin
Latent Heat
The heat energy released or absorbed at constant temperature per unit mass for change of state is called latent Heat.
Q = mL
L= latent heat
m= mass of substance
Water equivalent
It is the quantity of water whose thermal capacity is same as the heat capacity of body . it is denoted by W
W= ms
Hoar Frost
The conversion of solid into vapour state is called hoar frost
Sublimation
The direct conversion of solid into vapour state is called Sublimation.
Boiling point
It is the temperature at which liquid get boils is called boiling point
Melting Point
Conversion of solid into liquid at constant temperature is called Melting .
Surface tension and Surface energy
Its is the property of any type of liquid by virtue of which it try to minimize its surface area.
it is measured force acting on imaginary line per unit length that is drown tangential to the free surface of liquid
Mathematically given as
S = F/L = (work done)/(change in area)
It is scalar quantity
Surface tension is the molecular phenomenon cause due to cohesive force.
Surface tension of
liquid depend upon
Surface tension of liquid is independent upon
it is measured force acting on imaginary line per unit length that is drown tangential to the free surface of liquid
Mathematically given as
S = F/L = (work done)/(change in area)
It is scalar quantity
Surface tension is the molecular phenomenon cause due to cohesive force.
Surface tension of
- Only Nature of liquid
Surface tension of liquid is independent upon
- The surface area of film
the maximum distance upto which a molecule can exert a force of attraction or repulsion on other molecule is called molecular range
In solid and liquid it is of the order of 10^-9 m .
Surface energy
On increasing the free surface area of liquid ,work has to be done against the force of tension .
this work done stored in liquid surface as a potential energy .
This Additional potential energy per unit area of free surface of liquid is called surface energy.
surface energy = surface tension * increase in surface area .
Alpha, Beta and Gamma Rays Explanation
The existence of the three distinct types of radiations, α, β and γ−rays can be easily found by the following experiment.A small amount of radium is placed at the bottom of a small hole drilled in a lead block, which is kept in an evacuated chamber
A photographic plate is placed at a short distance above the lead block. A strong magnetic field is applied at right angles to the plane of the paper and acting inwards. Three distinct traces can be seen on the photographic plate when it is developed. The trace towards left is due to positively charged particles. They are named α -particles.The trace towards the right is due to negatively charged particles.They are named β-particles.The undeviating trace is due to neutral radiations which are called γ−rays.If an electric field is applied, the α-rays are deflected towards then negative plate,β−rays towards the positive plate and γ−rays are not deflected.
Spectral series of Hydrogen atom
Spectral series of hydrogen atom
Whenever an electron in a hydrogen atom jumps from higher energy level to the lower energy level, the difference in energies of the two levels is emitted as a radiation of particular wavelength. It is called a spectral line.
As the wavelength of the spectral line depends upon the two orbits (energy levels) between which the transition of electron takes place, various spectral lines are obtained. The different wavelengths constitute spectral series which are the characteristic of the atoms emitting them. The following are the spectral series of hydrogen atom.
- Lyman series
- Balmer series
- Paschen series
- Brackett series
- Pfund series
Breif Explanation of Rutherford Model of atom
Rutherford suggested the following Model of the atom.
- Atom may be regarded as a sphere of diameter 10 angstrom but whole of the positive charge and almost the entire mass of the atom is concentrated in a small central core called nucleus having diameter of about 10 to the power -14 m
- As the atom is electrically neutral, the total positive charge of the nucleus is equal to the total negative charge of the electrons in it.
- The electrons in the atom were considered to be distributed around the nucleus in the empty space of the atom.If the electrons were at rest, they would be attracted and neutralized by the nucleus. To overcome this, Rutherford suggested that the electrons are revolving around the nucleus in circular orbits,so that the centripetal force is provided by the electrostatic force of attraction between the electron and the nucleus.
Drawbacks of Thomson Atomic Model
Drawbacks
- According to electromagnetic theory, the vibrating electron should radiate energy and the frequency of the emitted spectral line should be the same as the electron. In the case of hydrogen atom, Thomson’s model gives only one spectral line of about 1300 Å. But the experimental observations reveal that hydrogen spectrum consists of five different series with several lines in each series.
- It could not account for the scattering of α-particles through large angles
Thomson atomic model
From the study of discharge of electricity through gases, it became clear that an atom consists of positive and negative charges J.J. Thomson tried to explain the arrangement of positive charge and the electrons inside the atom. According to him, an atom is a sphere of positive charge having a radius of the order of 10 angstrom. The positive charge is uniformly distributed over the entire sphere and the electrons are embedded in the sphere of positive charge. The total positive charge inside the atom is equal to the total negative charge carried by the electrons, so that every atom is electrically neutral.According to Thomson, if there is a single electron in the atom( hydrogen atom), the electron must be situated at the center of the positive sphere. For an atom with two electrons (helium atom), the electrons should be situated symmetrically with respect to the center of the sphere i.e opposite sides of the center at a distance of 2r, where r is the radius of the positive sphere. In a three electron system of the atom, the electrons should be at the corners of a symmetrically placed equilateral triangle, the side of which was equal to the radius of the sphere. In general, the electrons of an atom are located in a symmetrical pattern with respect to the center of the sphere. It was suggested that spectral radiations are due to the simple harmonic motion of these electrons on both sides of their mean positions. Moreover, the stability of the atom was very well explained on the basis of this model.
Tangent galvanometer
Tangent galvanometer
Tangent galvanometer is a device used for measuring current. It works on the principle of tangent law. A magnetic needle suspended at a point where there are two crossed fields at right angles to each other will come to rest in the direction of the resultant of the two fields.
Construction
It consists of a circular coil of wire wound over a non magnetic frame of brass or wood.The vertical frame is mounted on a horizontal circular turn table provided with three leveling screws. The vertical frame can be rotated about its vertical diameter. There is a small upright projection at the center of the turn table on which a compass box is supported. The compass box consists of a small pivoted magnet to which a thin long aluminium pointer is fixed at right angles. The aluminium pointer can move over a circular scale graduated in degrees. The scale consists of four quadrants. The compass box is supported such that the center of the pivoted magnetic needle coincides with the center of the coil. Since the magnetic field at the center of the coil is uniform over a very small area, a small magnetic needle is used so that it remains in an uniform field even in deflected position. Usually the coil consists of three sections of 2,5 and 50 turns, which are of different thickness, used for measuring currents of different strength.
Theory
When the plane of the coil is placed parallel to the horizontal component of Earth’s magnetic induction and a current is passed through the coil, there will be two magnetic fields acting perpendicular to each other (1) the magnetic induction (B) due to the current in the coil acting normal to the plane of the coil and (2) the horizontal component of Earth’s magnetic induction (Bh),Due to these two crossed fields, the pivoted magnetic needle is deflected through an angle θ. According to tangent Law,
B = Bhtanθ........(1)
If a current I passes through the coil of n turns and of radius a, the magnetic induction at the center of the coil is
B = μnI/2a...........(2)
Substituting equation (2) in equation (1)μnI/2a= Bhtanθ
∴. I = (a2B/μn) *tan θ
I = K tanθ...................(3)
where K = 2aBh/μn is called the reduction factor of the tangent galvanometer. It is a constant at a place. Using this equation, current in the circuit can be determined. Since the tangent galvanometer is most sensitive at a deflection of 45 degree, the deflection has to be adjusted to be between 30 and 60 degree.
Tangent galvanometer is a device used for measuring current. It works on the principle of tangent law. A magnetic needle suspended at a point where there are two crossed fields at right angles to each other will come to rest in the direction of the resultant of the two fields.
Construction
It consists of a circular coil of wire wound over a non magnetic frame of brass or wood.The vertical frame is mounted on a horizontal circular turn table provided with three leveling screws. The vertical frame can be rotated about its vertical diameter. There is a small upright projection at the center of the turn table on which a compass box is supported. The compass box consists of a small pivoted magnet to which a thin long aluminium pointer is fixed at right angles. The aluminium pointer can move over a circular scale graduated in degrees. The scale consists of four quadrants. The compass box is supported such that the center of the pivoted magnetic needle coincides with the center of the coil. Since the magnetic field at the center of the coil is uniform over a very small area, a small magnetic needle is used so that it remains in an uniform field even in deflected position. Usually the coil consists of three sections of 2,5 and 50 turns, which are of different thickness, used for measuring currents of different strength.
Theory
When the plane of the coil is placed parallel to the horizontal component of Earth’s magnetic induction and a current is passed through the coil, there will be two magnetic fields acting perpendicular to each other (1) the magnetic induction (B) due to the current in the coil acting normal to the plane of the coil and (2) the horizontal component of Earth’s magnetic induction (Bh),Due to these two crossed fields, the pivoted magnetic needle is deflected through an angle θ. According to tangent Law,
B = Bhtanθ........(1)
If a current I passes through the coil of n turns and of radius a, the magnetic induction at the center of the coil is
B = μnI/2a...........(2)
Substituting equation (2) in equation (1)μnI/2a= Bhtanθ
∴. I = (a2B/μn) *tan θ
I = K tanθ...................(3)
where K = 2aBh/μn is called the reduction factor of the tangent galvanometer. It is a constant at a place. Using this equation, current in the circuit can be determined. Since the tangent galvanometer is most sensitive at a deflection of 45 degree, the deflection has to be adjusted to be between 30 and 60 degree.
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