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Thread: Physics  Tips
 March 6th, 2015, 10:14 AM #1
Physics  Tips
MEMORIZE THESE :
Translational motion x = x 0 + v 0 t + 1/2at2 Vƒ = Vo + at
Frictional force f max = μ Ν μk < μs always
Uniform circular motion Fc = mac = mv2 /r ac= v2 /r
Momentum, Impulse I = F Δt = ΔM M = mv
Work, Power W = F d cosθ P = ΔW/Δt
Energy (conservation) ET = Ek + Ep E = mc2
Spring Force, Work F = kx W = kx2 /2
Continuity (fluids) A v = const. ρAv = const.
Current and Resistance I = Q/t R = ρl/A
Resistors (series, par.) Req = R1 + R2 . . . 1/ Req = 1/ R1 +1/ R2
Sound dB = 10 log 10 (I/I0 ) beats = Δ f
Kirchoff's Laws Σi = 0 at a junction ΣΔV = 0 in a loop
Thermodynamics Q = mc Δ T (MCAT !) Q = mL
Torque forces L1 = F1× r1 (CCW + ve) L2 = F2 × r2 (CW ve)
Torque force at EQ ΣFx = 0 and ΣFy = 0 ΣL = 0
Refraction ( sin θ1 )/(sin θ2 ) = v1 /v2 = n2 /n1 = λ1 /λ2 n = c/
USED AS PAIRS :
Memorize as Pairs
F = ma F = qE Similar Form
F = KG ( m1 m2 / r2 ) F = k ( q1 q2 / r2 )
V = IR P = IV Paired Use
vav = Δ d / Δ t aav = Δ v / Δ t (avg vel, acc)
v = λ f E = hf (f = 1/T)
Ek = 1/2 mv2 Ep = mgh (kin, pot E)
Ρ = F/A Δ Ρ = ρgΔh (pressure Ρ)
SG = ρ substance / ρ water ρ = 1 g/cm3 = 103 kg/m3 (Spec Grav)
ρ = mass / volume Fb = Vρg = mg (buoyant F)
Irms = Imax / √2 Vrms = Vmax / √2 Root Mean Sq
1/ i + 1/ o = 1/ f = 2/r = Power M = magnification =  i/o Optics
Note: Specific gravity (SG) is equivalent to the fraction of the height of a buoyant object below the surface of the fluid.
DON’T MEMORIZE,KNOW HOW TO USE :
Ρ + ρgh + 1/2 ρv2 = constant Bernouilli's Equation Fluids in Motion
L = L0 (1 + αΔ T ) Linear Expansion Solids, Temp Δ
A = A0(1 + γΔ T ) Area Expansion
V = V0(1 + βΔ T ) Volume Expansion β = 3 α
fo = fs (V ± vo )/( V ± vs ) Doppler Effect: when d is decreasing use + vo and  vs
V = Ed for a parallel plate capacitor d = the distance between the plates
dF = dq v(B sin α) = I dl(B sin α) Laplace's Law RH rule
1/ Ceq = 1/ C1 + 1/ C2 + 1/ C3 . . . Capacitors in Ser. and Par. Ceq = C1 + C2 . . .
Potential Energy ( PE ) = W = 1/2 QV Work in Electricity W = 1/2 CV2
ΔG = ΔH  TΔS Gibbs Free Energy ΔG° = RTln Keq
ATOMIC PHYSICS :
1) alpha (α) particle = 2He4 (helium nucleus);
2) beta (β) particle = 1e0 (an electron);
3) a positron +1e0 (same mass as an electron but opposite charge);
4) gamma (γ) ray = no mass, no charge, just electromagnetic energy;
5) Δ m /Δ t = rate of decay where Δ m = change in mass, Δ t = change in time.
6) If the number of halflifes n are known we can calculate the percentage of a pure radioactive sample left after undergoing decay since the fraction remaining = (1/2) n .
Nelectrons = 2 n2 , where Nelectrons designates the number of electrons in shell n .
The state of each electron is determined by the four quantum numbers:
• principal quantum number n determines the number of shells, possible values are: 1 (K), 2 (L), 3 (M), etc...
• angular momentum quantum number l, determines the subshell, possible values are: 0 (s), 1 (p), 2 (d), 3 (f), n1, etc...
• magnetic momentum quantum number ml , possible values are: ± l , ... , 0
• spin quantum number ms ,determines the direction of rotation of the electron, possible values are: ±1/2.
THE BASIC :
sin θ = opp/hyp cos θ = adj/hyp tan θ =opp/adj
θ = sin 1 x arcsec θ = sec1θ r2 = x2 + y2
• angle θ may be given in radians (R) where 1 revolution = 2πR = 360°
• estimate square root 3 as 1.7 and root 2 as 1.4
• crosssectional area of a tube = area of a circle = πr2 where π can be estimated as 3.14 and r is the radius of the circle; circumference = 2πr
SOME UNITS TO MEMORIZE :
Both work and energy are measured in joules where 1 joule (J) = 1 N × 1 m . {Imperial units: the footpound , CGS units: the dynecentimeter or erg }
The SI unit for power is the watt (W) which equals one joule per second (J/s) = volts × amperes .
Current is measured in amperes = coulombs/sec. The units of resistance are ohms, symbolized by Ω (omega), where 1 ohm = 1 volt/ampere.
The SI unit for pressure is the pascal (1 Pa = 1 N/m2 ). Other units are: 1.00 atm = 1.01 × 105 Pa = 1.01 bar = 760 mmHg = 760 torr.
The SI unit for the magnetic induction vector B is the tesla where 1 T = 1 N/(A)(m) = 104 gauss.
   Updated   
General Concepts on Electrical Circuits
I=GV and V=IR R=1/G
Where G is the conductance which is help offered to current by conductor and its unit is (ohm)^1
R=pl/A where p is resistivity and its unit is Ohm m
Series and parallel Resistance circuits
Series:
• One common end of both of the resistances
• Same current passes through both resistances or conductances connected in series
• Current is same
• Voltage is divided ; V=IReq = IR1 + IR2 = V1 + V2
• Resistances are added up
• Conductances reciprocals area added
• Voltage is divided due to resistive characteristic across resistances
• Voltage division rule is used to find voltage without current.
Vx= [Rx/Rt] Vs where Vx is unknown and Rt is total resistances and Rx is the resistance across which voltage has to be found.
Parallel:
• Both ends of two resistances must be common .
• Current is divided
• Voltage remains same
• Conductances are added up
• Resistances reciprocals are added up
• Current Division rule is used to find current without voltage
Ix= [Rn/Rn+Rx] Is
Where Ix is unknown and Rn is the resistance other than unknown one and is given where Rx is the resistance across which current has to be found.
“So many of our dreams at first seem impossible, then they seem improbable, and then, when we summon the will, they soon become inevitable.”
Christopher Reeve  March 7th, 2015, 03:24 PM #2
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if we do this is the hard portion gonna b done?
 March 7th, 2015, 07:31 PM #3“So many of our dreams at first seem impossible, then they seem improbable, and then, when we summon the will, they soon become inevitable.”
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