NEET_JEE_NCERT_TRICKS

2021-09-28 20:39:44 Notes on Wave Optics

Huygens Principle:- Wave-front of a wave, at any instant , is defined as the locus of all the particles in the medium which are being disturbed at the same instant of time and are in the same phase of vibration.

(a) Each point on a wave front acts as a source of new disturbance and emits its own set of spherical waves called secondary wavelets. The secondary wavelets travel in all directions with the velocity of light so long as they move in the same medium.

(b) The envelope or the locus of these wavelets in the forward direction gives the position of new wave front at any subsequent time.

Determination of Phase Difference:-
The phase difference between two waves at a point will depend upon

(a) The difference in path lengths of the two waves from their respective sources.
(b) The refractive index of the medium
(c) Initial phase difference between the source if any.
(d) Reflections, if any, in the path followed by waves.

Reflection of plane wave at plane surface (Laws of reflection):-

a) The incident ray, the reflected ray and normal to the reflecting surface at the point of incidence, all lie in one plane and that plane is perpendicular to the reflecting surface.
b) The angle of incidence is equal to the angle of reflection.

So, ∠i = ∠r

This signifies angle of incidence is equal to the angle of reflection.

Refraction of light:-
Refraction is the phenomena by virtue of which a wave going from one medium to another undergoes a change in velocity.

(a) The sine of the angle between the incident ray and the normal bears a constant ratio to the sine of the angle between refracted ray and the normal.

sin i/sin r = v1/v2 = 1µ2 = constant

Here, v1 and v2 are the velocities of sound in first and second medium respectively.1µ2 is the refractive index of the second medium with respect to first.

(b) The incident ray, the refracted ray and the normal to the refracting surface lie in the same plane.

Interference:- The modification in the distribution of light energy obtained by the superposition of two or more waves is called interference.

Principle of superposition:- It states that a number of waves travelling, simultaneously, in a medium behave independent of each other and the net displacement of the particle, at any instant, is equal to the sum of the individual displacements due to all the waves.

Displacement equation:- y = R sin 2π/λ (vt+x/2)

Amplitude:- R = 2a cos πx/λ

Intensity:- I = K4a2 cos2 (πx/λ) [I = KR2]

Maxima:- A point having maximum intensity is called maxima.

x = 2n (λ/2)

A point will be a maxima if the two waves reaching there have a path difference of even multiple of λ/2.

Imax = 4Ka2 = 4i (Here, i = Ka2)

Minima:- A point having minimum intensity is called a minima.
x = (2n+1) (λ/2)

A point will be a minima if the two waves reaching there have a path difference of odd multiple of λ/2.

Imin = K. 4a2×0 = 0

Condition for constructive interference:-
Path difference = (2n)λ/2

Phase difference = (2n)π

Condition for destructive interference:-
Path difference = (2n+1)λ/2

Phase difference = (2n+1)π

Coherent Sources:- Coherent sources are the sources which either have no phase difference or have a constant difference of phase between them.
Conditions for interference:-
(a) The two sources should emit, continuously, waves of same wavelength or frequency.

(b) The amplitudes of the two waves should be either or nearly equal

(c) The two sources should be narrow.

(d) The sources should be close to each other.

(e) The two sources should be coherent one.

Young’s double slit experiment:-
Path difference, x = yd/D

Maxima, y = nλD/d

Here, n = 0,1,2,3….

Minima, y = (2n+1) λD/d

Here, n = 0,1,2,3….

Fringe Width:- It is the distance between two consecutive bright and dark fringes.
β = λD/d

Displacement of fringes due to the introduction of a thin transparent medium:-
(a) Shift for a particular order of fringes:-

?y = (β/λ) (µ-1)t

(b) Shift across a particular point of observation:-

µ = (mλ/t) +1

Lloyd’s single mirror:-
?λ = β .2a/D

Power of lens:- P = 100/f Open / Comment

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2021-09-27 19:25:02 Important Points of NCERT

1. 1935 : Stanley - Crystallised viruses.
2. 1937 : Ramde o Misra obtained Ph.D. in Ecology from Lee ds university (U.K.).
3. 1938 : Coelocanth fish caught in South Africa.
4. 1945 : Fleming, Chain & Florey - Awarded Nobel prize.
5. 1950 : Watson obtained Ph.D. on a study of the effect of hard X-rays on bacteriophage multiplication.
6. 1951 : Family planning programme started in India.
7. 1952 : Hershey & Chase-experiment on bacteriophage or Bacterial virus
gives unequivocal proof that DNA is the genetic material.
8. 1953 : Miller experiment - Methane, ammonia, hydrogen & water vapour.
9. 1953 : Watson & Crick - Double helical structure of B-DNA & replication scheme.
10 . 1953 : Palade : Discovered ribosome.
11 . 1954 : Ramachandran - Triple helical model of collagen, published in Nature.
12 . 1954 : Crick complete d Ph.D. on a thesis “X-rays diffraction :
polypeptides and proteins.
13 . 1958 : Meselson & Stahl - Work on E.coli proves semiconservative
replication of DNA in prokaryotes.
14 . 1958 : Taylor - Work on Vicia faba proves semiconservative replication of DNA in eukaryotes.
15. 1960 : Katherine Esau - Published “Anatomy of Seed Plants.”
16. 1961 : Melvin Calvin - Nobel Prize.
17. 1962 : Watson, Crick and Wilikins - Nobel Prize.
18. 1963 : Wheat varieties (Sonalika & Kalyan sona) introduced.
19. 1963 : Two enzyme responsible for restricting growth of bacteriophage
in E.coli were isolated.
20. 1966 : Derivative of IR-8 & Taichung native-I introduced.
21. 1969 : Whittaker - Five kingdom classification. Open / Comment

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2021-09-27 06:01:20 Structure and Functions of different parts of Brain

Specialisation of the nervous system in general and of the brain in particular has been the most significant feature in evolution of mammals, reaching its heights in primate mammals, and its epitome in man. Thus, the human brain is comparatively very large in proportion to body size. It weighs about 1380 gm in an average adult man and about 1250 gm in an average adult woman.

It is divisible as follows :

(a) Forebrain (prosencephalon): Includes olfactory lobes,cerebrum and diencephalon.
(b) Midbrain (mesencephalon): Includes a pair of cerebral peduncles and four rounded eminences, called corporaquadrigemina.
(c) Hindbrain (Rhombencephalon): Includes cerebellum,pons and medulla oblongata.

@Science_Wallah

Detailed notes of Brain coming soon... Open / Comment

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2021-09-26 18:08:32 Important Points of NCERT -

A mere 0.1 per cent impurities make domestic sewage unfit for human use :

Impurities 0.1%

1. Suspended solids, e.g., sand, silt and clay.
2. Colloidal material, e.g., Fecal matter, bacteria, cloth and paper fibres.
3. Dissolved materials, e.g., nutrients (nitrate, ammonia, phosphate, sodium,
calcium).

Daphnia is the indicator of BOD
Water hyacinth (Eichhornia crassipes), the world's most problematic aquatic weed, also called 'Terror of Bengal'.
Minamata disease is cause in humans in Japan by biomagnification of mercury (Hg)
The concentration of DDT is increased at successive trophic levels; say if it starts at 0.003 ppb (ppb = parts per billion) in water, it can ultimately can reach 25 ppm (ppm = part per million) in fish- eating birds, through biomagnification. Open / Comment

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2021-09-26 10:40:36 Chemistry In Everyday life -

Histamine,stimulates the secretion of pepsin.
Histamine is a potent vasodilator . lt contracts the smooth muscles in the bronchi.
Synthetic drugs brompheniramina ( Dimetapp) & terfenadine ( Seldane), act as antihistamines.
Antiallergic & antacid drugs work on different receptors.
Tranquilizer & analgesics are neurologically active drugs.
Noradrenaline plays a role in mood changes.
Chlordiazepoxide & meprobamate,are sutable for relieving tension.
Equanil is used in controlling depression & hypertension.
Barbiturates are hypnotic.
Analgesics reduce or abolish pain.
Aspirin & paracetamol are non - narcotic analgesics.
Aspirin inhibits the synthesis of prostaglandins. It use in prevention of heart attacks
Morphine is a narcotic analgesics.
The first effective anti bacterial agent prontosil.
Antibiotics have either cidal effect or a static effect on microbes.
Penicillin G has a narrow spectrum of. Ampicillin & Amoxicillin are synthetic modifications of penicillins.
In India, penicillin is manufactured at the Hindustan Antibiotics in Pimpri & in private sector industry.
Chloramphenicol, Vancomycin. & Ofloxacin are a broad spectrum antibiotics.
Antiseptics ( either kill or prevent the growth of microorganisms).
Dettol is a mixture of chloroxylenol & terpineol.
Iodine is a powerful antiseptic.
0.2% solution of phenol is an antiseptic while it's 1% solution is disinfectant.
Norethindrone is an synthetic progesterone derivative drug.
The estrogen derivative drug is ethynylestradiol.
Aspartame is the most successful artificial sweeteners.
Alitame is high potency sweeteners, although it is more stable than aspartame.
Sucralose is trichloro derivative of sucrose.It does not provide calories.
The two most familiar antioxidants are butylated hydroxy toluene (BHT) & butylated hydroxy anisole(BHA). Open / Comment

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