Fundamental Constants

Transcription

1 Fundamental Constants Atomic Mass Unit u kg MeV c 2 Avogadro s number N A (g mol) 1 Bohr magneton μ B (31) J/T Bohr radius a (24) m Boltzmann s constant k (12) J/K Compton wavelength λ C (22) m Deuteron mass m d (20) kg (24) u Electron mass m e (54) kg (13) 10-4 u (15) MeV/c 2 Electron-volt ev (49) J Elementary charge e (49) C Gas constant R (70) J/K mol Gravitational constant G (85) N m 2 /kg 2 Hydrogen ground state E (40) ev Josephson frequency-voltage ratio 2e (14) Hz/V

2 Magnetic flux quantum ɸ (61) Wb Neutron mass m n (10) kg (14) u (28) MeV/c 2 Nuclear magneton µ n (17) J/T Permeability of free space µ 0 4ᴫ 10-7 N/A 2 (exact) Permittivity of free space ϵ C 2 /N m 2 (exact) Planck s constant h ħ (40) J s (63) J s Proton mass m p (10) kg (12) u (28) MeV/c 2 Quantized Hall resistance h/e (12)Ω Rydberg constant R H (13) 10 7 m -1 Speed of light in vacuum c m/s (exact)

3 Commonly Used Formulas with Description Electric Fields 1. F = k q 1 q 2 r 2 Where, electric force between two charges k N m2 C 2, Coulomb constant Or k = 1 4πε 0 2. E F q 0, electric field vector Or E = k q r 2 r 3. E = k qi i r 2 r i, superposition of electric fields i 4. E = k qi 0 lim qi i r 2 i r i = k dq r 2 r, total electric field at a point in space due to an element of charge

4 Gauss Law 5. Φ = EA = E Surface da, electric flux 6. Φ c = E da = E n da, net electric flux through a closed surface 7. Φ c = E da = q in ε 0, Gauss Law Where q in = the charge inside the Gaussian surface 8. The following are simplified calculations from applying Gauss Law a. Insulating sphere of radius R E = k Q at r > R r 2 E = k Q r at r < R R3 b. Thin spherical shell of radius R E = k Q at r > R r 2 E = o at r < R c. Line charge of infinite length and charge per unit length λ E = 2k λ r, outside the line charge

5 d. Nonconducting, infinite charged plane with charge per unit area σ E = σ 2ε 0, everywhere outside the plane e. Conductor of surface charge per unit area σ E = σ ε 0, just outside the conductor E = 0, inside the conductor Electric Potential B 9. U = q 0 E A ds, change in potential energy 10. V = U q 0 Where B = E A ds, potential difference 1V = 1 J C 11. V = Ed, potential difference between two points in a uniform electric field E Where d is the displacement in the direction parallel to E

6 12. V = k q, potential due to a point charge q r Where r is the distance from the charge 13. U = k q 1 q 2, potential energy of a pair of point charges separated r 12 by distance r V = K dq r, electric potential for a continuous charge distribution 15. a. E x = dv, x component of an electric field potential in a 3 dx dimensional system b. Ey = dv dy, y component c. Ez = dv dz, z component 16. The following are simplified electric potential calculations for various charge distributions. a. Uniformly charged ring of radius a V = k center. Q, Along the axis of the ring, a distance x from its x 2 +a 2

7 b. Uniformly charged disk of radius a V = 2πkσ[ x 2 +a 2 x], along the axis of the disk, a distance x from its center c. Uniformly charged, insulating solid sphere of radius R and total charge Q V = k Q r, at r R V = kq 3 r 2, at r < R 2R R2 d. Isolated conducting sphere of total charge Q and radius R V = k Q, at r R R V = k Q r, at r > R Magnetic Fields 17. F = qv B, magnetic force that acts on a charge q moving with a velocity, v 18. F = qvbsinθ, magnitude of the magnetic force Where θ is the angle between v and B and B = T = Wb m 2 = N A m

8 19. F = Il B, The force on a conductor of length l carrying a current I while placed in a uniform external magnetic field B 20. df = I ds B, force on a very small segment ds 21. μ = IA, magnetic moment of a current loop A is perpendicular to the plane of the loop and A is equal to the area of the loop 22. τ = μ B, torque on a current loop placed in a uniform external magnetic field. 23. r = mv qb, the radius r of the circular path a charged particle moves in a perpendicular plan to the magnetic field. m is the mass of the particle 24. ω = qb m, cyclotron frequency 25. F = qe + qv B, Lorente Force

9 Magnetic Field Source 26. db = k m Ids r r 2, Biot-Savart law km = 10 7 Wb A m 27. B = μ 0I 2πa, Magnetic field of an infinite long wire where the field lines are concentric with the wire. 28. F = μ 0I1I2, Force per unit length between two wires. l 2πa 29. B ds = μ 0 I, Ampère s Law 30. B = μ 0NI 2πr, Magnetic field inside a toroid N= number of turns N 31. B = μ 0 I = μ l 0nI, Magnetic field inside a solenoid 32. Φ m B da, Magnetic flux

10 33. B ds = μ 0 I + μ 0 I d, Generalized format of Ampère s Law I d 0 dφ e dt, Displacement current Electromagnetic Waves E = μ x E 0, property of electric field, wave equation t B x 2 = μ 0 2 B t 2, Property of magnetic field, wave equation 36. C = 1 μ 0 0 = 3.00x10 8 m s, The speed of electromagnetic waves in a vacuum 37. E B = C, The instantaneous magnitudes of E and B in an electromagnetic wave are related by this expression. 38. S 1 μ 0 E B, Poynting vector, the rate of flow of energy, in electromagnetic waves, crossing a unit area. 39. P = S c, Pressure exerted by electromagnetic on incident surface under complete absorption.

11 40. E = E m cos(kx ωt), electric field of a sinusoidal plane wave propagating in the positive direction along x axis. 41. B = B m cos(kx ωt), magnetic field of a sinusoidal plane wave propagating in the positive direction along x axis. Since ω = 2ωf and k= 2ᴫ/λ, we find that 42. ω k = λf = c 43. S av = E m B m 2μ 0 = E 2 m = 2μ 0 C C 2μ 0 B m 2, The average value of a Poynting vector for a plane electromagnetic wave. Superconductivity 44. B c T = B c 0 [1 T T c 2 ], Critical magnetic field as a function of temperature, T, for type I superconductor (sc). T c = Critical Temperature of a given sc

12 45. M = B = xb, magnetization of an SC exposed to magnetic field, μ 0 B x = 1 μ 0, magnetic susceptibility 46. E g = 3.53 kt c, Energy gap of an SC representing the energy required to break up one Cooper pair which is proportional to the critical temperature at T=0K Courtesy of Serway, Physics for Scientists and Engineers