Physics laws and formulae (O level)

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

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Kinematics

• $latex average\ speed = \frac{total\ distance\ moved} {time\ taken}$
• $latex velocity = \frac{distance\ moved\ in\ a\ specified\ direction} {time\ taken}$
• $latex velocity = \frac{displacement} {time\ taken}$
• $latex acceleration = \frac{change\ in\ velocity} {time\ taken}$

Equations of motion with constant acceleration

• $latex v = u+at$
• $latex s = \frac{(u+v)t}{2}$
• $latex s = ut + \frac{1}{2}at^2$
• $latex v^2= u^2+2as$

Density

• $latex \rho = \frac{m}{V}$

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.
• $latex F = ke$

Forces

• 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.
• $latex F = ma$
• $latex W = mg$

Circular motion

• $latex F = \frac{mv^2}{r}$

Moments

• 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

• $latex momentum = mass \times velocity$

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.
• $latex work\ done = force \times distance\ moved\ in\ the\ direction\ of\ the\ force$
• $latex power = \frac{work\ done}{time\ taken}$
• $latex power = \frac{energy\ transfered}{time\ taken}$
• $latex efficiency = \frac{useful\ energy\ output}{total\ energy\ input} \times 100%$
• $latex efficiency = \frac{work\ done\ on\ load}{work\ done\ by\ effort} \times 100%$
• $latex Kinetic\ energy = \frac{1}{2}mv^2$
• $latex Potential\ energy = mgh$

Pressure

• $latex Pressure = \frac{force}{area}$
• $latex Liquid\ pressure = \rho gh$

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.
• $latex \frac{p_1v_1}{T_1} = \frac{p_2v_2}{T_2}$

Thermal Physics

• $latex Q = mc \Delta \theta$
• $latex Q = ml$

Waves and optics

• Law of reflection – The angle of incidence is equal to the angle of reflection.
• $latex v = f\lambda$
• $latex f = \frac{1}{T}$
• $latex refractive\ index = \frac{speed\ of\ light\ in\ vacuum}{speed\ of\ light\ in\ medium}$
• $latex n = \frac{\sin i}{\sin r}$

Magnetism

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

Electricity

• 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.
• $latex Q = It$
• $latex E = QV$
• $latex E = ItV$
• $latex V = IR$
• $latex R = \frac{\rho l}{A}$
• $latex P = IV$
• $latex P = \frac{V^2}{R}$
• $latex P = I^2R$

Resistors in series

• $latex R_{total} = R_1 + R_2 + R_3$

Resistors in parallel

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

Electromagnetism

• 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.

Sydney Chako

Mathematics, Chemistry and Physics teacher at Sytech Learning Academy. From Junior Secondary School to Tertiary Level Engineering Mathematics and Engineering Science.