In the beginning
Thomson's experiments
1. He observed that negative particles ( later called electrons) have very less mass
2. Nature of the negative particle is independent of both the electrode material as well as the gas used in the discharge tube.
Now, Why did Thomson do the cathode ray experiment? Because Perrin had found that cathode rays deposited an electric charge. Thomson wanted to see if, by bending the rays with a magnet, he could separate the charge from the rays.
Plum pudding model
First proposed by J. J. Thomson in 1904 soon after the discovery of the electron. It stated:-
1. Overall the atom is neutral.
2. It looked like the English desert plum pudding
(Or a watermelon, how seeds in watermelon are random)
3. The electrons are randomly arranged throughout the atom (just as seeds in the watermelon)
Millikan's oil drop experiment
Malikon observe that electric charge of the charge to drops were always a multiple of -1.6×10-¹⁹ C. He proposed that they should be the charge of an electron.
Rutherford's gold foil experiment
1. Most of the particles where undeflected but a small fraction where deflected by a small angle.
2. 1/20000 of the alpha particles is deflected back at an angle of 180°. This leads to the conclusion that atom consists of positively charged mass at the centre which lead to discovery of nucleus and it also concluded that almost the entire mass of the atom is from the nucleus.
Rutherford's atomic model
1. An atom has a tiny dense Central core called nucleus which contains the entire mass and is positive charge.
2. Radius of nucleus = 10-¹⁵
• Radius of atom = 10-¹⁰
3. Electrons revolve around the nucleus in circular orbits of very high speeds.
4. Electrons and nucleus are held together by electrostatic force of attraction. (K = q 1 q 2 / r²)
5. Rutherford's experiment on scattering of alpha-particles showed for the first time that the atom has nucleus.
6. When Alpha particles are sent through a thin metal foil, most of them go straight through the foil because
1. Most part of the atomic empty space.
2. Alpha particles move with high velocity.
Properties of a positive ray
1. Positive rays are composed of positively charged particles called protons.
2. They travel in a straight line and are deflected by electric as well as magnetic fields, indicating that they are positively charged.
3. The charged to mass ratio (e/m) of positive particles varies with the nature of gas placed in the discharge tube. Also the posses many times the mass of electron.
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• Charge of a proton is equal and opposite to the charge of an electron
Ep = 1.602 × 10-¹⁹ C
Ep = charge of proton
Atomic number is denoted by z
Z = number of protons.
• So in general, the number of protons in the nucleus of the atom is equal to the atomic number (Z).
• Also, The number of electrons in a neutral atom is equal to the number of protons.
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• The number of protons in the hydrogen nucleus is 1 and hence the atomic number is also 1.
Example:-
Number of protons in copper wire = 29
Atomic number of copper wire = 29
For a neutral atom
Number of electron = number of protons = atomic number (z)
Charge of the nucleus = Total charge of proton
Mass of the nucleus = total mass of protons and neutrons
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Isobars and isotopes
Isotopes
• Atoms with identical atomic number but different atomic mass number is called isotopes.
Isotones
• The elements having the same number of neutrons (number of neutrons = mass number - number of protons) is called isotones.
Ex:- chlorine and potassium have same number of neutrons which is 20.
Isobars
• Elements with same mass number but different atomic number are called isobar.
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Frequency
It is the number of waves passing through a particular point in one second.
Speed of wave (v) = μ × Î»
μ = frequency
v = 3 × 10⁸
λ = wavelength
Let's solve one question regarding frequency
Q. The frequency of yellow light having wavelength of 600 nanometer is
Ans:- v = μ × Î»
Where,
v = 3 × 10⁸
λ = 6 ×10-⁷
μ = ?
3 × 10⁸ = μ × 6 ×10-⁷
μ = 5 × 10¹⁴ Hz
SI unit of frequency is hertz (Hz).
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What is electromagnetic radiation
• It prefer to the waves of an electromagnetic field propagating through space carrying electromagnetic energy
Electromagnetic waves could be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields
• when a charged particle accelerates it will emit electro magnetic waves.
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Black body radiation
• In 1900, Max plank proposed that the energy observed or emitted by atoms or molecules is quantized.
He hypothysized the radiant electromagnetic energy E = nhv , where n is = to 1,2,3.......
This hypothesis correctly explained the intensity versus wavelength graph for black body radiation.
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Planck's Quantum hypothesis
Planck hypothysized that atoms and molecules could emit or observe energy only in discrete quantities, like small packets or bundles called quanta.
Quanta ! The smallest quantity of energy that can be emitted or observed in the form of electromagnetic and radiation.
The energy of a single quanta of electromagnetic energy is given by E = hμ, where h is the planck's constant.
Energy = h×μ
h = planck's constant
μ = frequency
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Photoelectric effect
1. The number of electrons ejected is proportional to the intensity of light.
2. No of electrons can be ejected if frequency (μ) of the light is lower than a certain threshold frequency, which depends upon the identity of metal.
3. The kinetic energy of the ejected electron is proportional to the difference between the frequency of incident light and the threshold frequency.
According to the law of conservation of energy,
Input energy = output energy
The incident energy
E = hμ = Φ + 1/2 Me × u²
Φ (work function) is the minimum amount of energy required to dislodge and electron from metal surface.
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Emission and absorption spectra
1. Emission
The spectrum of radiation emitted by a substance that has absorbed energy is called emission spectrum.
2. Absorption
When white light is passed through unexcited atomic hydrogen and then through a slit and prism, the transmitted light is lacking in intensity at the same wavelength as emitted in the corresponding emission spectrum.
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Bohr's postulates
1. An electron in an atom can only exist in stationery States.
2. An electron moving in stationery state does not emit electromagnetic radiation.
3. Radiation is emitted or absorbed only when an electron jumps from one energy level to another.
4. Electron can only have angular momentum given by,
Mevr = (n × h ) / 2Ï€
Limitations of bohr's model
1. Bohr's model worked very well only for single electron species, But failed for multi electron species.
2. Bohr's model failed to explain splitting of spectral lines.
3. Bohr's model model contradicted with the Heisenberg uncertainty principle.
4. It could not explain the ability of atoms to form molecules by chemical bonds.
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De Broglie's Hypothesis
• Louis De Broglie proposed that all matter can exhibit wave like behaviour.
• The de broglie wavelength ( λ ) associated with a massive particle is related to its momentum (p) through the planck's constant h.
λ = h / p
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Uncertainty principle
• It is impossible to know simultaneously both the momentum, defined as mass time velocity and the position of a particle.
P and x are complementary
Complementary:- it holds that object have complementary properties which cannot be observed or measured simultaneously.
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Quantum mechanics
We have studied a lot about protons and neutrons till now. Did you know, protons and neutrons are actually made of quarks which are indivisible. A proton contains 2 up quark and 1 down quark. Similarly, a neutron contains to down quark and one up quark.
Electrons together with "up" and "down" quark seem to be all we need, to build atoms and therefore describe normal matter. A nucleus is held with strong force another fundamental force of the standard model. Just as protons carry electromagnetic force, particles called gluons carry strong force.
High energy experiments reveal that there are 6 quarks
Why are three (and only three) different versions of each of these particles remains a mistry.
The same was found for electrons, which have heavier siblings called the muon and tau.
The heavy particles are only produced in high energy collisions and are not seen in everyday life.
Why are heavy energy particles not seen in everyday life?
Because they decay very quickly into the lighter particles, such decays involves the exchange of force carrying particles called the w and z, which unlike the photon have mass.
These both w and z carry the week force, The final force of the standard model.
The same force (weak force) allows protons and neutrons to transfer into each other.
To observe the w and z directly, we need the high energy collision provided by particle accelerator.
Neutrino (another particle of standard model) interact with another particles through weak force. Trillions of neutrino many generated by sun fly through us every second. Measurement of weak interaction find that there are different kinds of neutrons associated with electron muon and tau.
All this particles have antimatter versions, which have the opposite charge. Matter and antimatter particles are produced in pairs in high energy collisions.
Higgs boson
A Quantum triple in the background field of universe. Interacting with this field is how all the fundamental particles acquire mass, the Atlas experiment on the large hadron collider is studying the standing model in depth. But taking precise measurements of the particle and forces that make up the universe. At last resist can look for answers to mystery is not explain by the standard model. Some mysteries are:-
1. How does gravity fit in?
2. What is the real relationship between force carriers and matter particles.
3. How can we describe dark matter which makes up most of the mass in the universe but remains and uncounted for?
These are some of the questions that are remained unsolved.
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Schrödinger's cat
A cat is placed with a scaled vial of position that will break at a random time, since no one know when the poison has been released or if the poison has been released, until the boxes opened, the cat can be thought as both "alive"and "dead" at the same time. The same sort of things happens to physical system at Quantum scales, like an electron orbiting in an hydrogen atom. The electron is not orbiting at all, it's sort of everywhere in the space all it once showed in the GIF below.
With more probability of being at some places than others, and it's only after we measure its position, then we can say, where is it at that moment.
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Quantum entanglement
Suppose, instead of one cat in 1 box, now we have 2 cats and 2 box, each cat in one box. If we repeat Schrödinger's cat experiment with this pair of cats, the outcome of the experiment can have four possibilities.
Either both will be alive or both will be dead or one will be alive and other will be dead. Showed in the table below
The system of the both cats is again in a superposition state, where each outcome will be having a 25% chance. But quantum mechanics tells us its possible to erase both (s.no 1 and 2) from the superposition state. We are erasing them because Schrödinger's thought experiment tells us that either the cat will be alive or dead. In other words they would be 2 cat system where one is alive and the other is dead (s.no 3 and 4 can be considered). The technical term for this is, the states of the cats are entangled. But there is something mind blowing here, no matter how far you keep 2 entangle boxes, if we open the box and cat is alive then, we can tell that the other is dead without opening the box. Let's understand it with an example:-
Take two boxes with a cat in each. Connect the boxes with a poison that can break at anytime and entangle them. Keep the boxes as far as possible (you can also keep it in the end point of the universe) if you open the box and the result of the box is alive, then we can say that the result of second box is dead without opening it.
How is possible? How the states of cat are entangled no matter how far they are. Also they are too far away to communicate with each other in time, so how do the two poisons act such that, one blows up and the other doesn't? If till now you are thinking this is just an hypothetical case, then you are wrong. It has been experiment in real world, it turns out that subatomic particles and entangled in a superposition state, where if one spins one way then the other must spin the other way even though there is no way for information to pass from one particle to another.
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Teleportation
Anton Zeilinger is a long way from teleporting himself or any other human. But he is trying to use Quantum entanglement to teleport tiny individual particles, in this case photons, particles of light. He starts by generating entangled photons in a lab on the Iceland of lapama. One entangled Photon stays in lapama while the other is sent by laser to the Iceland of tencrife (89 miles away)
Now Zeilinger bring in a third Photon the one he wants to teleport and has it interact with the entangled photon on lapama. The team studies the interaction comparing the quantum states of two particles and here is the amazing part, because of spooki action at distance, the team is able to transfer the entangle photon on the distant Island into identical copy of that third Photon. It's like if the third Photon has teleported across the sea without travelling the space between the Iceland. Can we (humans) teleport! Since we are made of particles could this process make humans teleportation possible one day, suppose there are two chambers one in Florida and the other in New York.
Now, the chamber of particle in Florida is entangled with another chamber of particles in New York. While the device scans the huge number of particles of a body (more particles than in observable universe). It's jointly scanning the particles in the other chamber and it creates a list that compares the quantum state of two sets of particles and here is where entanglement comes in, because of spooky action at a distance, the list also reveals how the original state of human particle is related to the state of the particles in Florida. Next, the operator sends the list to New York, there they use the data to reconstruct the exact Quantum state of every single one of human particle and new human materialises. It's not that the particle travelled from Florida to New York its that entanglement allows human Quantum state to be extracted from Florida and reconstruct it in New York. In the particle of the human in Florida has been destroyed.
Now, the question is, is that the same person that arrived at New York or is it a different one.
Well there should be no difference between new person and the old person and the reason is that, according to quantum mechanics, it's not the physical particles that make person it's the information this particles contain and that information has been teleported exactly for all the trillions of particles that make up persons body.
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