IIT JEE MAIN

2021-07-15 16:34:26 #JEEMains #News
JEE Mains 2021: 4th session dates postponed, exams to be held on 26th, 27th & 31st August, and on 1st and 2nd September, 2021

Tweet
@physicswallahlakshyavideos
@iit_jee_main ओपन / कमेंट

2021-07-12 23:58:33 QUICK REVISION
FORMULAS

1. Formulas related to force:
F = ma
F = kx
F = m(vf² - vi²/2S)
F = mv/t
F = md/t²
F = m(vf - vi)/t
F = Area × density × velocity²
F = 1/2 mv²/d
F = 1/2 Pv/d
F = Power/velocity
Fc = mv²/r
Fc = mrw²
Fc/2 = mv²/2r
Fc = 2K.E/r
F = Area × Stress
F = pir² × stress
F = YA × Strain
F = YAl/L
F = pressure × area
F = change in momentum × time interval
F = - 2mVx × Vx/2l
F2 = F1/A1 × A2
F = qE
F = kQ/r²
F = ILB sintheta
F = q (v × B)
F = qE + q(v × B)

2. Formulas related to energy and work
Fd = k.e
mgh = 1/2 mv²
E = 1/2 kx²
E = Ve
E = nhf
E = nhc/lambda
E = Pc
K.e = hf - work function = hf - hf° = hf - hc/w° (here w° is cutt off wavelength)
E = 1/2 Pv
mv²/2r= Fc/2
K.E/r = Fc/2
K.E = Fc×/r/2
K.e = 1.5 KT
E = VQ
E = Power × time
E = Fvt
% loss in K.e = v1² - v2²/v1² × 100
% loss in P.e = h1² - h²/h1² × 100
Energy lost due to air friction(Fh) = 1/2mv² - mgh (when body is thrown upward)
Energy lost due to air friction(FS) = mgh - 1/2mv² (when body is thrown downward)
E = 1/2 CV² (capacitor)
E = R × hc (R is Rydberg' constant)
J = m-¹ × Js ms-¹
hf kalpha x rays = EL - Ek
hf kbeta x rays = EM - Ek
Binding energy = mass defect × c²
W = Fd Costheta
W = nmgh (when person is climbing stairs)
W = n(m+m) gh (when person is climbing stairs with some load)
W = 0mgh + 1mgh + 2mgh + 3mgh ....... (in case of stacking bricks. For ist brick h=0. For 2nd brick h=1. For 3rd brick h=2 and so on)
W = Fd = PA × change in V
W = Q - change in U
Q = mc × change in T
T/273.16 = Q/Q3 (Thermodynamic scale)
W = I²Rt
W = emf×charge
W = VQ
W = 1/2 lF
W = YAl²/2L
W = StressAl²/2Strain
W = PressureAl²/2Strain
W = Fl²/2Strain

3. Formulas related to Power
P = Fv
P = E/t
P = n(mgh/t)
P = Fd/t
P = mv²/2t

4. Formulas related to distance, displacement, velocity and accelration
d = vt
d = at²
d = (vf + vi/2) ×t
d = 5t² (for distance in 'n' seconds)
d = 5(2tn - 1) (for distance in 'nth' second)
d = 1/2 mv²/F
d = vit + 5t²
d = v × underroot 2H/g
d = vt = x°wt = x°2pi/T × t = x°2pift
x = x° Sin wt
x = x° Sin (underroot k/m) t
vf = vi + at
2as = vf² - vi²
2as = (vi + at)² - vi²
2as = vf² - (vf - at) ²
v = underroot Vfx² + Vfy²
v = Power/Force
v = 2×K.E/momentum (k.e = 1/2 Pv)
v² = 2×Power×time/mass (P = mv²/2t)
v = underroot 2as
v = underroot gr (speed at highest point in a verticle circle)
v = underroot 5gr (speed at lowest point in a verticle circle)
v² = 2FS/m
v² = 2E/m
v² = 2Ve/m
v = eBr/m (velocity of particle under action of magnetic force along circular path)
v² = Force/Area.Density
v = w underroot x°² - x²
v = underroot k/m × underroot x°² - x²
v = x°w (at mean position where x=0)
v = x° underoot k/m
v = v° underroot 1 - x²/x°² (for determining ratio b/w inst. Velocity and maxi. Velocity)
v= x°2pif = x°2pi/T
a = x°w² = x°w.w = vw = v.2pif
Common velocity = m1v1/m1+m2
vi² = Rg/Sin2theta
v = underoot Tension×length/mass
V = 2pi ke²/nh (speed of e- in nth orbit)
Vn = V/n
v = nh/2pimr (lambda = 2pir and lambda=h/p)
ma = kx
a = kx/m (SHM)
a = - gx/l (Simple pendulum)
ac = v²/r

5. Formulas related to wavelength 'w'
w = v/f
w = 1/wave number
w1 = 2l (when pipe is opened at both ends)
w1 = 4l (when pipe is opened at one end)
Delta w = Us/f (doppler shift)
Wavelength for obs. = w - delta w = v/f - Us/f
w = hc/Ve
w = hc/E
w = h/mv
w = h/P as P = underroot 2mE so
w = h/underroot 2mE (de Broglie wavelength)
w = underroot 150/V A° (short method for de Broglie wavelength. This formula is applicable only for e-)
1/w = RH (1/p²-1/n²)
Wmaxi/Wmini = n²/n²-p² (for determining ratio b/w maxi. Wavelength to mini. Wavelength for series of atomic spectrum)
w = 2pir/n (n is no. of loops in a circle)
h/mv = 2pir.

@iit_jee_main @iit_jee_main ओपन / कमेंट

2021-07-11 15:33:38 KVPY Fellowship-2021
@iit_jee_main ओपन / कमेंट

2021-07-10 12:35:28 Get Kota top teachers, toppers hand written notes at an unbelievable low price, only on BooksBear

Download our app now and check out BooksBear exclusive notes

https://booksbear.page.link/PHYSICSWALLAH
https://booksbear.page.link/PHYSICSWALLAH

We have also organised a free book giveaway in the app for u all.

U can use code PHYSICSWALLAH to get even more discount on every product listed on the app ओपन / कमेंट

2021-07-09 17:30:52 Properties of Solids and Liquids - Revision Notes on Liquids at Rest:

Force of cohesion:- It is force between two molecules of similar nature.

Force of adhesion:- It is the force between two molecules of different nature.

Molecular range:- The maximum distance between two molecules so that the force of attraction between them remains effective is called molecular range.

Sphere of influence:- Sphere of influence of any molecule is the sphere with molecule as its center and having a radius equal to molecular range (=10-7 cm).

Surface film:- Surface film of a liquid is defined as the portion of liquid lying on the surface and caught between two parallel planes situated molecular range apart.

Surface Tension

Surface tension is the property of a liquid by virtue of which its free surface behaves like a stretched membrane and supports, comparatively heavier objects placed over it. It is measured in terms of force of surface tension.

Force of surface tension:- It is defined as the amount of force acting per unit length on either side of an imaginary line drawn over the liquid surface.

(a) T = Force/length = F/l

(b) T = Surface energy/Surface area = W/A

Units:- S.I – Nm-1

C.G.S- dyn cm-1

Additional force:-
(a) For a cylindrical rod:- F = T×2πr (Here r is the radius of cylindrical rod)

(b) For a rectangular block:- F = T×2(l+d) (Here l is the length and d is the thickness of the rectangular block)

(c) For a ring:- F = T×2×2πr (Here r is the radius of cylindrical rod)

Surface energy:-
Potential energy per unit area of the surface is called surface energy.

(a) Expansion under isothermal condition:-

To do work against forces of surface tension:-

W= T×A (Here A is the total increase in surface area)

To supply energy for maintaining the temperature of the film:-

E = T+H

(b) Expansion under adiabatic conditions:-

E = T

Force of surface tension is numerically equal to the surface energy under adiabatic conditions.

Drops and Bubbles:-

(a) Drop:- Area of surface film of a spherical drop of radius R is given by, A = 4πR2

(b) Bubble:- The surface area of the surface films of a bubble of radius R is, A = 2×4πR2

Combination of n drops into one big drop:-

(a) R = n1/3r

(b) Ei = n (4πr2T), Ef =4πR2T

(c) Ef/ Ei = n -1/3

(d) ΔE/Ei = [1-(1/n1/3)]

(e) ΔE = 4πR2T (n1/3-1) = 4πR3T (1/r – 1/R)

Angle of contact:- Angle of contact, for a pair of solid and liquid, is defined as the angle between tangent to the liquid surface drawn at the point of contact and the solid surface inside the liquid.

(a) When θ < 90º (acute):-

Fa >Fc/√2

(i) Force of cohesion between two molecules of liquid is less than the force of adhesion between molecules of solid and liquid.

(ii) Liquid molecules will stick with the solid, thus making solid wet.

(iii) Such liquid is put in the solid tube; it will have meniscus concave upwards.

(b) When θ > 90º (obtuse):-Fa
(i) Force of cohesion between two molecules of liquid is less than the force of adhesion between molecules of solid and liquid.

(ii) In this case, liquids do not wet the solids.

(iii) Such liquids when put in the solid tube will have a meniscus convex upwards.

(c) When θ = 90º:-?

Fa=Fc/√2

The surface of liquid at the point of contact is plane. In this case force of cohesion and adhesion are comparable to each other.

(d) cosθc = Tsa – Tsl/Tla

Here, Tsa,Tsl and Tla represent solid-air, solid-liquid and liquid-air surface tension respectively). Here θc is acute if Tsl < Tsa while θc is obtuse if Tsl >Tsa.

Capillarity:-

?Rise of Liquid in a Capillary Tube?Capillarity is the phenomenon, by virtue of which the level of liquid in a capillary tube is different from that outside it, is called capillarity.

Weight of liquid, W = Vρg = πr2[h+(r/3)]ρg (Here r is the radius meniscus)

If weight of meniscus is taken into account, the force of surface tension will be,

T = [r(h+(r/3)) ρg]/2 cosθ

For fine capillary, force of surface tension, T = rhρg/2 cosθ

So height, h = 2T cosθ/ rρg

@iit_jee_main @iit_jee_main ओपन / कमेंट

2021-07-08 00:30:59 Postulates of kinetic theory of gases

A gas consists of large number of tiny particles called molecules.
Volume occupied by gas molecules, is negligible as compared to the total volume of gas.

There is continuous rapid random motion of gas molecules. The molecules collide with each other and against walls of container.

The molecules are perfectly elastic bodies and there is no loss of kinetic energy during collisions.

There are no attractive forces between the molecules of gas.

The pressure exerted by a gas is due to bombardment of gas molecules against the walls of the container.

The different molecules possess different velocities and hence different energies. The average K.E. is directly proportional to absolute temperature.

@iit_jee_main @iit_jee_main ओपन / कमेंट

2021-07-06 17:09:16 JEE MAINS UPDATE

3rd phase
20 july - 25 july 2021

4th phase
27 july - 2 august

Only at - @iit_jee_main


-Those who didn't fill the form for JEE 3rd or 4th phase can now again fill the form for JEE 3rd phase from 6th July till 8th July ( online )
and for 4th phase from 9th July to 12th July .

- exam centers as compared to last time have been doubled .

- language choices have also been increased....


@iit_jee_main
@physicswallahlakshyavideos ओपन / कमेंट

2021-07-06 15:05:56 Tweet

@iit_jee_main
@physicswallahlakshyavideos ओपन / कमेंट

2021-07-05 21:38:50 #CBSE #NewAssessment
CBSE Class 10, 12 board exams for 2021-22 to be held in two terms

The CBSE has declared a special scheme for the assessment for board examinations for Classes 10 & 12 for the 2021-22 session.The academic session will be divided into two terms with approximately 50% syllabus in each term. The first term exams will be held in November-December 2021 and the second term exams will be scheduled for March-April 2022.

@physicswallahlakshyavideos
@iit_jee_main ओपन / कमेंट