 # GCSE Physics # Laws in GCSE Physics

Thermodynamics I - Energy dissipates in the form of heat.  100% efficiency is impossible.  Energy cannot be created or destroyed, just transferred from place to place, or form to form.  The total energy of any closed system is fixed.

Thermodynamics II – Heat moves from hot to cold, the rate of heat transfer depends upon temperature difference.  There is no such thing as "cold energy".

Newton I – If there is no resultant force there is no acceleration.

Newton II – F=ma  (Resultant force is proportional to mass and proportional to acceleration.)  F=(mv-mu)/t   Force is proportional to the rate of change of momentum.

Newton III – Actions have equal and opposite reactions (of the same type, in the same line.)  Momentum is always conserved in any collision.

Ohm's Law – Voltage and current are proportional.  V=IR   Resistance is defined as V/I in all situations.

Kirchoff I – The sum of the currents into a point equal the sum of the currents out of a point.  (Series I1 = I2 = I3 ...) (Parallel I1 = I2 + I3 + ...)

Kirchoff II – The sum of the rises and falls in potential around a closed circuit is zero. (Series V1 = V2 + V3 +...) (Parallel V1 = V2 = V3 = ...)

Using Ohm's Law it follows: (Series RT = R1 + R2 + R3 +...) (Parallel 1/RT = 1/R1 + 1/R2 + 1/R3 + ...)

Hooke's Law – Force is proportional to extension.  F=kx

Boyle's Law – Pressure is inversely proportional to volume, (for a fixed mass of gas at a constant temperature.)

Charles' Law – Volume is proportional to temperature, (for a fixed mass of gas at constant pressure.)

Pressure Law – Pressure is proportional to temperature, (for a fixed mass of gas at a constant volume.)

Snell's Law – Refractive index from medium a to b is equal to the ratio of sine of the angle in a to sine of the angle in b.  n = sinθa/sinθb