The phenomenon of photoelectric effect is discovered by Hertz in 1887
When the light of certain frequency is allowed to fall on a metal surface and electrons are ejected from the metal surface this phenomenon is called photoelectric effect
Or
The phenomenon of emission of electrons by metals when illuminated by light of suitable frequency
The photoelectric effect involves the conversion of light energy into electrical energy
Photo Electrons --
The ejected electrons from the metal surface when is suitable frequency of light falls on that metal surface are called photoelectrons
Number of photo electrons ejected =
Power / energy of photon
Threshold Frequency --
The minimum amount of frequency of incident light required to eject an electron from the metal surface is known as threshold frequency
Work function --
The minimum energy required by an electron to escape from the metal surface is called work function it is also known as threshold energy
Work function = h v o
Work function is measured in electron volt
1 eV = 1.602×10^-¹⁹. J
The work function depends --
1) properties of metal
2) nature of surface
Photons --
Light consists of packets of energy called photons photons are electrically neutral and not deflected by electric and magnetic field
Energy of photon -- hv.= hc/£
where
£ is wavelength ie lambda h is planck constant and v is frequency
Number of photons emitted = power / energy of photon
The photoelectric current
The photoelectric current depends upon
1) intensity of the light
2)
Potential difference applied between electrodes
3) nature of the emitter material
Cutoff voltage -- cutoff voltage is also known as stopping potential it depends upon
Cut off voltage is directly related to maximum kinetic energy of the emitted electrons
eVo = ½mv²
Stopping potential depends on
Frequency of incident light
Debroglie Wave length
Exercises
Que 1 find the debroglie wavelength for an electron moving with velocity 3.5 ×10⁵ metre per second
Que 2 find de broglie wavelength of a ball of mass 100 g moving with a velocity of 50 metre per second
Que 3. Find the de broglie wavelength of particle accelerating with a potential of 25 volt
Que 4 If kinetic energy of an electron is 3.2 joules find the debroglie wavelength of the particle
NCERT solutions for class 12 -Physics -Semiconductor devices
Semiconductor Devices
Semiconductors are the materials whose conductivity and resistivity lie in between metals and insulators
AC temperature higher than zero degree Kelvin some of the electrons are excited from valence band to conduction band creating an equal number of holes in the valence band
Silicon and germanium are the good examples of semiconductors
Types of semiconductors
Intrinsic semiconductor
The pure semiconductor is called intrinsic semiconductor in intrinsic semiconductors conductivity is due to holes and electrons both which increase with rise of temperature electrons move in antiparallel direction to the external field
Extrinsic semiconductors
When is small quantity of impurity is mixed in a pure aur intrinsic semiconductor the conductivity of semiconductor increases sach and impure semiconductor is called extrinsic semiconductor
There are two types of extrinsic semiconductors
n type
N type semiconductor pentavalent impurity are used as a dopant with silicon or germanium such a impurity called donor impurity because each dopant atom provides one free electron
p type
To prepare a p type semiconductor and trivalent impurity are used as a dopant with silicone or Germany I'm such an impurity is called as chapter impurities as he impurity atoms wants to accept an electron from the crystal lattice in p-type semiconductors each loop and atom provides a hole
Conduction Band
In conductors energy bands are very close or even overlapped by the conduction bands due to this reason the electrons can flow very easily from the valence band to the conduction band by electric field and Thus show conductivity
In the insulators the gap between valence bond and the conduction band is very large due to this reason the electrons cannot flow from valence band to conduction band by an electric field and Thus they do not show conductivity
In semiconductor the gap between valence band and conduction band is very small so the electrons can jump from valence band to conduction band by an electric field and show conductivity
Logic Gates Digital Electronics
Logic gate is a digital electronic circuit which follows a logical relationship between its input and output logic gates following Boolean algebra which consists of three basic operations
AND
NOT
OR
Communication System
This particular attach lecturer I explain the different topics of communication system like what is modulated wave what is amplitude modulated signal height of the antenna range of the antenna
In 1820 O rested observed that a compass needle shows deflection when brought near a current carrying wire this means electric current gives rise to magnetism
Bio t Savart Law --
This law gives magnitude of magnetic field at any point due to current carrying conductor
according to this law magnetic field dB at any point P due to current element idl is
dB = μ0 /4π . idl sin¢/r²
Where μ0 is absolute permeability of air
μ= 4π×(10)-⁷
Magnetic field due to current carrying straight wire
Magnetic field due to current carrying wire of finite length at a point p situated at a normal distance r is given by
B= μ0 I/4πr. (sina+sin b)
If a=b= 90°then
B = μ0 I/2πr
Motion of a charged particle in a uniform magnetic field
Particle carrying a positive charge q moving with a velocity vector v enters a magnetic field B it experiences a force which is given by the expression
F = qv B sin ¢
The force F is always perpendicular to the both velocity and the magnetic field trajectory of a charged particle depends upon the angle between velocity and the magnetic field
--- angle between them is zero degree that is they are parallel to each other v||B then
F= qv B = 0
-- angle between velocity of the particle and the magnetic field is 90 degree that is they are perpendicular to each other then force is maximum sin 90 =1
F= qv B
When force is maximum at provide centripetal force and the path of the particle is a circle so
the angular velocity of the particle is
Centripetal force = mv²/r= qv B
v/r= B q/m= w
Time period of rotation is 2π/w
T= 2π/w= B q/2πm
Magnetic force on a current carrying conductor (Lorentz Force)
If a current carrying conductor length l is placed in a magnetic field B such that it makes an angle with the direction of the field it experiences a force called Lorentz force and is given by
F = Bil sin¢
If if angle a zero degree then force = 0
angle is 90 degree then force is maximum
that F=Bil
Force between two parallel current carrying conductors
When two long straight conductor carrying currents i1 and i2 are placed parallel at a distance of a from each other then a mutual force of attraction acts between them
F= μ/4π. 2I1I1l/a
Where l is the length of that portion of the conductor on which force is to be calculated
Show the force per unit length is
F/l= μ/4π. 2I1I1/a
Watch the attached lecture for detailed concept and for solving numericals
Magnetic field due to solenoid
For a solenoid coil of infinite length at a point on its axial line of magnetic field is given by
At centre ---
B= μ0 n I
Where μ= 4π×10^-7
n is number of turns per unit length
I is the current
Magnetic field at the end of the solenoid
B= 1/2 μ0 n I
Magnetic field for toroidal solenoid
Ring shaped to solenoid is called a toroid
Magnetic field for the toroidal solenoid is same as the magnetic field for solenoid
B= μ0 n I
n=N/2πR and R is radius of toroid
Torque experienced by a current carrying loop in a uniform magnetic field
When a current carrying coil having N turns and area Ais placed in a uniform magnetic field B in such a way that the normal to the quiet makes an angle theta with the direction of the magnetic field in the coil experiences at torque given by
NIBA sin¢
When the plane of the coil is perpendicular to the field then torque is zero and when the plane of the coil is parallel to the field torque is maximum
Work done
If the coil is to be rotated through an angle from its equilibrium position then the required work done is
W= MB (1-cos¢)
Work done is maximum when angle is equal to 180 degree
W= 2MB
Moving coil galvanometer
In a moving coil galvanometer the coil is suspended between the pole pieces of a strong horseshoe magnet when the current will pass through this while then torque will be experienced by this coil
F= NB i l
Torque = NB i A
as the coil deflect restoring torque is set up in the suspension fibre
Torque =C¢
Where C is the toroisional constant of the fibre and ¢ is the angle of twist
So
NB iA =C¢
i=C¢/NBA
Where C/NBA is called galvanometer constant
Current sensitivity
IT is the deflection produced in the galvanometer per unit current flowing through it
=¢/i= NBA/C
Voltage sensitivity
It is defined as the deflection produced in the galvanometer per unit potential difference applied to it
=¢/V = NBA/RC
Conversion of galvanometer into ammeter and voltmeter
Conversion of galvanometer into ammeter
Ammeter is made by connecting a low resistance S in a parallel with the moving coil galvanometer G,Sis known as shunt
S/G=Ig/I- I g
Conversion of galvanometer into voltmeter
A voltmeter is made by connecting a resistor of high resistance R in series with a moving coil galvanometer G
G+R = V/Ig
Classification of magnetic substances
Substances are classified according to their magnetic behaviour
1) Diamagnetic substances
Substances when placed in magnetic field and magnetized opposite to direction of magnetising field that is they are repelled by magnet are called diamagnetic substances
Eg gold, silver
2) Paramagnetic substances
Substances which are magnetised in the direction of magnetising field these substances are attracted towards the magnet
Eg aluminium platinum
3) Ferromagnetic substances
Substances which are strongly magnetized in the direction of magnetising field are called ferromagnetic substances example iron nickel
Some important terms in magnetism
Magnetic induction (B)
If a piece of any substance is placed in an external magnetic field the substance becomes magnetize this is called induced magnetism and phenomena is called magnetic induction
It is a vector quantity denoted by B
SI unit is Tesla or Weber / metre ^2or N/Am
Intensity of magnetisation (M)
Intensity is the extent to which the substance is magnetized it is defined as magnetic moment per unit volume of the magnetized substance
M= m/V
m is magnetic moment of a magnetized substance of volume v Its SI unit is a A/m
Magnetic intensity or magnetic field strength (H)
The capability of magnetising field to magnetize the substance is expressed by vector H and magnetic intensity of the field
H= B/¥0 - M
Its unit is same as that of m that is A/m
Magnetic permeability
It is defined as ratio of magnetic induction inside the magnetized substance to the magnetic intensity of the magnetising field
SI unit is N/A^2 Or Tm/A or W b / Am
Relative magnetic permeability
What is the ratio of magnetic permeability of the substance to the permeability of the free space
Dimension less quantity and is equal to one for vacuum
Magnetic susceptibility
It is the ratio of intensity of magnetisation to the magnetic intensity of magnetisation field
it is also dimension less
In case of diamagnetic materials susceptibility is negative so it is independent of kelvin temperature T
In case of paramagnetic material susceptibility varies inversely to the temperature with the Curie's law
Xm= C/T
In case of ferromagnetic materials relationship between susceptibility and the temperature is known as Curie- Weiss Law
Xm = C/(T-Tc)
Curie temperature
The temperature above which a ferromagnetic substance becomes paramagnetic substance is COD Curie temperature of the substance Curie temperature for the iron is 770 degrees celsius
That is when we heat any ferromagnetic substance after a definite temperature the ferromagnetic substance becomes paramagnetic that temperature is called Curie temperature
What is magnetic flux
Number of lines of force per unit area normal to the force is called a magnetic flux
Magnetic flux is defined as product of magnetic field and area of the conductor
¢=BA cos ¢
Where B is magnetic field
A-- is area of surface
SI unit of magnetic flux is weber Wb
Watch the lecture
Earth magnetic field and magnetic elements
It is due to the rotation of the Earth where by various charged ions present in the molten state in the core of the earth rotate and it constitutes a current which is the reason for magnetic field of the earth magnitude and direction of the magnetic field of the earth at a place are completely given by a certain quantity is known as magnetic elements
Direction of the Earth's magnetic field is from the geographical South to the geographical north
Magnetic elements of the earth
1) Magnetic declination is the angle between the geographic and magnetic meridian planes
2) Magnetic dip It is also known as angle of inclination
It is the angle between the direction of intensity of total magnetic field of the earth and a horizontal line in the magnetic meridian
3) Horizontal component of the earth magnetic field
Earth magnetic field is horizontal only at the equator
at any place the total intense de can be resolved into horizontal component and the vertical component
Horizontal component--
BH= B cos ¢
Vertical component
B v = B cos ¢
Total intensity
B= ✓B²H+B²v
At equator vertical component of the magnetic field is 0 while and the bowl horizontal component of the magnetic field is zero
Electric charges is of two types positive and negative loss of electrons gives positive charge and gain of electrons gives negative charge to a body
SI unit of charge is Coulomb
Dimensional formula is [AT]
Quantization of charge
The charge on a body is integral
multiple of e
Q=ne
Charge distribution
Charges distributed along the line but is called linear charge density that is charge per unit length is called linear charge density
= ∆q/∆l
Charges distributed over a surface area then it is called surface charge density
=∆q/∆S
Main charge is distributed over entire volume of a body that is call volume charge density
=∆q/∆V
Watch the lecture to solve problems on quantization of charges
Coulomb's Law
If q1 and q2 be the two stationary point charges in free space separated by a distance r then force of attraction or repulsion between them is
F=k( q1 q2 )/r^2
Where k =9×10^9=1/4πEo
Eo -- electric permittivity of free space
Value is equal to 8.85×10^-12
If some dielectric medium (K) is field between the charges then coulomb force become
F'=F/K
Watch the lecture to solve questions on coulombs law
What is electric Dipole
Dipole consists of two equal and opposite charges separated by a small distance
Dipole moment of a dipole is defined as the product of magnitude of either charges and the distance between them
(+q)---------------------------------(-q)
2a
Dipole moment (p) = distance ×charge
= 2aq
Dipole moment is a vector quantity its direction is from negative to positive charge SI unit is coulomb metre
Dimensional formula is [LTA]
Watch the lecture for numericals
Electric field intensity at any point on axis of dipole
Auto point restaurant r from the centre of a reliable along its axial line electric field due to a dipole is equal to
E= k 2pr/(r^2-a^2)^2
K = 9×10 ^9
If r>>a
Then
E= k 2p/r^3
Watch the lecture for derivation
Electric field intensity at a equitorial point due to a dipole
E= - k p/(r^2 +a^2)^3/2
E= - kp/r^3
Torque on a dipole
When a dipole is placed in an external electric field making an angle with the direction of the uniform electric field
It experiences a torque = pE sin¢
Work done
An electric dipole initially kept in an uniform electric field making an angle and rotated so as to finally substance and another angle then the work done for rotating the dipole is
W= pE (cos¢2. - cos ¢1)
Potential energy of a dipole
The amount of work done in rotating an electric dipole from a direction perpendicular to electric field to a particular direction
U = -pE cos ¢
potential energy of an electric dipole is a scalar quantity that is measured in joule
Lecture on Torque on a dipole
Electric flux and Gauss theorem
What is Resistance , specific Resistance
When resistance are connected in series
What is capacitor and define capacitance
Different combinations of capacitance
Part 1
Part 2
Part 3
What is parallel plate capacitor
Numericals on parallel plate capacitor
Electric potential
Part 1
Part 2
Part 3 numericals
What is Relation between Electric field intensity and electric potential
Transverse waves are those waves whose medium particles travel in a direction which is perpendicular to the direction of propagation eg light waves
Longitudinal waves -- the waves whose medium particles travel and same direction to the direction of propagation for example sound waves
Characteristics of wave
Different elements of array used to describe any wave are
Wave length-- Maximum distance between two consecutive crust is called wavelength Its SI unit is metre
Time period -- time taken to complete one vibration is called time period SI unit is second
Frequency -- Number of vibrations done in one second is frequency Its unit is Hertz
Watch the lecture --
Numerical
Interference of waves
Interference of Light part 2
Topic discussed in attached lecture are
What are coherent sources
What are conditions when we get Dark or Bright fringe
Path difference
Interference part 3
What is formula for fringe width and angular fringe width
Standing waves
Longitudinal waves are those waves in which medium particles travel in the same direction that is in the direction of the propagation eg sound waves
In transverse wave crest and trusts are found where as in longitudinal waves compression and rare fractions are formed
In order to solve the numericals related with wave motion what's the lecture given below the question covered in that lecture is
What is wave motion
Speed of wave
Phase difference
Path difference
Doppler Effect
Mr Doppler explains that when two or more waves travel in the same direction or in the opposite direction then we hear the sound which is the interference of the two waves
That is when the two sound waves travel in same direction or in the opposite directions of different frequencies we hear a frequency which is different from their actual frequency explain the formula by which we can easily find out the frequency which we hear which is known as Doppler effect in the two videos which are attached below explain the tricks and different numericals for different cases by watching that educational lecture you can easily understood what is Doppler effect and how will you solve different types of problems
Doppler Effect
Beats
Diffraction
Diffraction is the phenomena which is observed in the case of the waves when the waves travel in the medium and when they fall around the corners of any object they get diffracted
Attached below eye explain the different formula for the diffraction and the theoretical concept of the diffraction
Photoelectric effect--
The phenomenon of photoelectric effect is discovered by Hertz in 1887
When the light of certain frequency is allowed to fall on a metal surface and electrons are ejected from the metal surface this phenomenon is called photoelectric effect
Or
The phenomenon of emission of electrons by metals when illuminated by light of suitable frequency
The photoelectric effect involves the conversion of light energy into electrical energy
Photo Electrons --
The ejected electrons from the metal surface when is suitable frequency of light falls on that metal surface are called photoelectrons
Number of photo electrons ejected =
Power / energy of photon
Threshold Frequency --
The minimum amount of frequency of incident light required to eject an electron from the metal surface is known as threshold frequency
Work function --
The minimum energy required by an electron to escape from the metal surface is called work function it is also known as threshold energy
Work function = h v o
Work function is measured in electron volt
1 eV = 1.602×10^-¹⁹. J
The work function depends --
1) properties of metal
2) nature of surface
Photons --
Light consists of packets of energy called photons photons are electrically neutral and not deflected by electric and magnetic field
Energy of photon -- hv.= hc/£
where
£ is wavelength ie lambda h is planck constant and v is frequency
Number of photons emitted = power / energy of photon
The photoelectric current
The photoelectric current depends upon
1) intensity of the light
2)
Potential difference applied between electrodes
3) nature of the emitter material
Cutoff voltage -- cutoff voltage is also known as stopping potential it depends upon
Cut off voltage is directly related to maximum kinetic energy of the emitted electrons
eVo = ½mv²
Stopping potential depends on
Frequency of incident light
Nature of the emitter material
Cut off voltage does not depend upon the intensity of the light
The current whose magnitude keeps on changing continously with time between 0 and a maximum value and the direction also reverses periodically is called alternating current
i= i0sinwt =i0sin2πnt = i0sin 2πt/T
i - instantaneous value of current
i0 - peak value of current
w= angular frequency in rad/sec
n= frequency in Hz
T= time period
Root mean square value (rms)
Root mean square of current in an AC circuit for one complete cycle is called RMS value
i(rms)=i0/√2
RMS value of alternating current is also called virtual value or effective value
Mean or average value (i(av))
The average of instantaneous values of current in one cycle is called its mean value the average value of alternating quantity for one complete cycle is zero
The average value of alternating current over half cycle is
iav= 2i0/π
Impedence
Z= √{(Xl~Xc)^2+ R^2}
Resonant frequency
w0= 1/√LC
v0 = 1/2π√LC
Resonant frequency does not depend upon the resistance of the circuit
Resonant frequency admittance is minimum and impedance is maximum
Quality Factor
Quality factor of the circuit determines the sharpness of resonance
Formula
Q= wL/R = 1/wRC
AC Generator
An electrical machine used to convert mechanical energy into electrical energy is known as a c generator it works on the principle of electromagnetic induction that is when a coil is rotated in a uniform magnetic field and induced EMF is produced in it
induced emf = -Nd¢/dt = NBAwsinwt
Current in coil =
i= e/ R
Transformer
It is a device which raises or lowers the voltage in alternating circuits through mutual induction it was on the basic principle of mutual induction that is alternating current passing through primary coil creates a continuously changing flux through the air the changing flux induces an alternating EMF and the secondary coil in an ideal transformer there is no loss of power
The waves in which electric and magnetic fields vary sinusoidally in space and with time the electric and magnetic fields are mutually perpendicular to each other and also to the direction of propagation of the wave
Displacement Current
The plates of a charged capacitor a joint through a conductor then the charge arises due to flow of electrons and conduction current flows in the conductor Maxwell proposed that as the charge on the plates of capacitor decreases the electric field between the plates also decreases with time and time varying electric field produces magnetic field which signifies there must be some current flowing between the plates this current is known as displacement current
Ampere maxwell law
Maxwell in 1862 case the basic laws of electricity and magnetism in the form of four fundamental equations which are known as Maxwell equations
1 Gauss law of electrostatics
Just now give the total electric flux in the terms of the charge enclosed by the closed surface
This law states that the electric lines of force start from positive charge and end at negative charge that is electric lines of force do not form a continuous closed path
InE.ds= q/€o
2 Gauss law for magnetism
This law shows that number of magnetic lines of force entering a closed surface is equal to the number of magnetic lines of force leaving that closed surface
Bds=0
3 Faraday law of electromagnetic induction
It gives relationship between electric field and changing magnetic flux It tells that changing magnetic field is the source of the electric field
E.dl= d¢/dt
¢= flux
4 Ampere Maxwell law
Law states that a magnetic field can be produced by a conduction current as well as by displacement current
At any instant in a circuit the conduction current is equal to the displacement current
Relation between Electric and Magnetic Field
E=B×C
E is electric field
B is magnetic field
C is speed of light
Energy density of electromagnetic wave
Energy density is defined as energy crossing through unit area in unit time
Watch lecture in order to understand how to solve the different questions based on electromagnetic waves