IMPORTANT FORMULAS

• Maximum number of electrons that can be accommodated in a shell = 2n²
  where 'n' is the number of the given shell from the nucleus.


• MIRROR FORMULA:
  
  (1/v) + (1/u) = (1/f) = (2/R)
  
  Where u, v, f and R are object distance, image distance, focal length of mirror and radius of curvature of mirror, respectively.


• LENS FORMULA:
  
  (1/v) - (1/u) = (1/f)
  
  Where u, v and f are object distance, image distance and focal length of lens, respectively.


• MAGNIFICATION:
  
  m = (h'/h) = (-v/u) for mirror
  
  m = (h'/h) = (v/u) for lens
  
  Where m, h' and h are magnification, image height and object height, respectively.


• η₂₁ = (sin i/sin r)
  
  Where η₂₁, i and r are refractive index of medium 2 with respect to medium 1, angle of incidence and angle of refraction, respectively.


• η₂₁ = (v₁/v₂)
  
  Where η₂₁, v₁ and v₂ are refractive index of medium 2 with respect to medium 1, speed of light in medium 1 and speed of light in medium 2, respectively.


• η_m = (c/v)
  
  Where η_m, c and v are absolute refractive index of a medium, speed of light in vacuum and speed of light in the medium, respectively.


• P = (1/f)
  
  Where P and f are power of lens in dioptre and focal length of lens in metre, respectively.


• I =(Q/t)
  
  Where I, Q and t are current in ampere, charge in coulomb and time in seconds, respectively.


• V = (W/Q)
  
  Where V, W and Q are voltage(potential difference) in volt, work done in joule and charge in coulomb, respectively.


• V = IR
  
  Where V, I and R are voltage in volt, current in ampere and resistance in ohm, respectively.


• R = ρ(l/A)
  
  Where R, ρ, l and A are resistance in ohm, resistivity in ohm-meter, length of the conductor in meter and cross-sectional area of conductor in m², respectively.


• R = R₁ + R₂ + R₃ +....
  
  Where R is the equivalent resistance of R₁, R₂, R₃,...connected in series.


• R = (1/R₁) + (1/R₂) + (1/R₃) +....
  
  Where R is the equivalent resistance of R₁, R₂, R₃,...connected in parallel.


• H = VIt = I²Rt
  
  Where H, V, I, R and t are heat produced in joule, voltage in volt, current in ampere, resistance in ohm and time in second, respectively.


• P = VI = I²R = (V²/R)
  
  Where P, V, I and R are power in watt, voltage in volt, current in ampere and resistance in ohm, respectively.


• 1 kWh = 3.6 x 10⁶ joule
  
  [kWh is kilowatthour also called 'unit' of electrical energy]