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Physics laws and formulae (O level)

Physics laws and formulae (O level)

This list is a list of physics laws and formulae used in O level physics.


  • average\ speed = \frac{total\ distance\ moved} {time\ taken}

  • velocity = \frac{distance\ moved\ in\ a\ specified\ direction} {time\ taken}

  • velocity = \frac{displacement} {time\ taken}

  • acceleration = \frac{change\ in\ velocity} {time\ taken}

Equations of motion with constant acceleration

  • v = u+at

  • s = \frac{(u+v)t}{2}

  • s = ut + \frac{1}{2}at^2

  • v^2= u^2+2as


  • \rho = \frac{m}{V}

Hooke’s law

  • Hooke’s law – that the extension was of a material is proportional to the stretching force provided the material is not permanently stretched.

  • F = ke


  • Parallelogram law – If two forces acting at a point are represented in size and direction by the sides of a parallelogram, their resultant is represented in size and direction by the diagonal of the parallelogram drawn at that point.

  • Newton’s first law of motion – A body stays in its state of rest or uniform velocity unless acted upon by an external force.


  • Newton’s second law of motion – The acceleration of a body is directly proportional to the resultant force acting on it.

  • Newton’s third law of motion – To every action there is an equal and opposite reaction.

  • F = ma

  • W = mg

Circular motion

  • F = \frac{mv^2}{r}


  • Law of moments – When a body is in equilibrium the sum of the clockwise moments about any point is equal to the sum of the anticlockwise moments about the same point.

  • moment of a force = force × perpendicular distance of the line of action of the force from the pivot


  • momentum = mass \times velocity

Work, energy and power

  • Law of conservation of energy – energy can neither be created nor destroyed but can be converted from one form to another.

  • work\ done = force \times distance\ moved\ in\ the\ direction\ of\ the\ force

  • power = \frac{work\ done}{time\ taken}

  • power = \frac{energy\ transfered}{time\ taken}

  • efficiency =  \frac{useful\ energy\ output}{total\ energy\ input} \times 100%

  • efficiency =  \frac{work\ done\ on\ load}{work\ done\ by\ effort} \times 100%

  • Kinetic\ energy = \frac{1}{2}mv^2

  • Potential\ energy = mgh


  • Pressure = \frac{force}{area}

  • Liquid\ pressure = \rho gh

Gas Laws

  • Boyle’s law – The pressure of a fixed mass of gas is inversely proportional to its volume if its temperature is kept constant.

  • Charles’s law – The volume of a fixed mass of gas is directly proportional to its absolute temperature if the pressure is kept constant.

  • Pressure law – The pressure of a fixed mass of gas is directly proportional to its absolute temperature if the volume is kept constant.

  • \frac{p_1v_1}{T_1} = \frac{p_2v_2}{T_2}

Thermal Physics

  • Q = mc \Delta \theta

  • Q = ml

Waves and optics

  • Law of reflection – The angle of incidence is equal to the angle of reflection.

  • v = f\lambda

  • f = \frac{1}{T}

  • refractive\ index = \frac{speed\ of\ light\ in\ vacuum}{speed\ of\ light\ in\ medium}

  • n = \frac{\sin i}{\sin r}


  • Law of magnetic attraction – Like poles repel, unlike poles attract.


  • Law of electrostatic attraction – Like charges repel, unlike charges attract.

  • Ohm’s law – The current in an ohmic conductor is directly proportional to the p.d. across its ends if the temperature is kept constant.

  • Q = It

  • E = QV

  • E = ItV

  • V = IR

  • R = \frac{\rho l}{A}

  • P = IV

  • P = \frac{V^2}{R}

  • P = I^2R

Resistors in series

  • R_{total} = R_1 + R_2 + R_3

Resistors in parallel

  • \frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}


  • Faraday’s law – The size of the induced p.d. is directly proportional to the rate at which the conductor cuts magnetic field lines.

  • Lenz law – The direction of the induced current is such as to oppose the change causing it.


1 thought on “Physics laws and formulae (O level)”

  1. Very nice and to the point revision notes
    I wish you can include the rest of topics like atomic physics and basics electronic.

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