Laws and Principles

Question 0

State BOYLE’S LAW

Answer 0

Pressure is inversely proportional to volume for a fixed mass of gas at constant temperature

         P₁V1 = P2V2

           P ∝ 1/V

Question 1

State ARCHIMEDES’ PRINCIPLE

Answer 1

When a body is wholly or partially submerged in a fluid, it experiences an upthrust equal to the weight of the fluid displaced

Question 2

State the CONDITIONS FOR EQUILIBRIUM

Answer 2

• The vector sum of the forces in any direction is Ø
• The vector sum of moments about any point is Ø
— this law is also known as the LAW OF THE LEVER or the PRINCIPLE OF MOMENTS

Question 3

State COULOMB’S LAW

Answer 3

The electrostatic force between two point charges is proportional to the product of their charges and inversely proportional to the square of the distance between them

F = Q₁Q2 / 4πεd^2

    F ∝ 1/d^2

Question 4

What is the DOPPLER EFFECT?

Answer 4

The DOPPLER EFFECT is the apparent change in frequency of a wave due to relative motion between the source and the observer

            f' = fc / c±u

Question 5

State EINSTEIN’S PHOTOELECTRIC LAW

Answer 5

The energy of the fastest electron emitted is the difference between the energy of the photon and the work function of the metal

          hf = Φ+(1/2)mv^2

               Φ = hf*

Question 6

State FARADAY’S LAW

Answer 6

The magnitude of induced emf is proportional the the rate of change of flux linking a circuit

                E = dΦ/dt

Question 7

State HOOKE’S LAW

Answer 7

When an object is stretched, bent or deformed, the restoring force is proportional to the displacement from its equilibrium position

                    F = –ks

                   k = mg/s

Question 8

State JOULE’S LAW

Answer 8

The rate of heat production in a conductor is proportional to the square of the current, provided its resistance is a constant

                 P = (I^2)R

                W = (I^2)Rt

                   P ∝ I^2

Question 9

State KEPLER’S THIRD LAW

Answer 9

The square of the periodic time of a satellite’s orbit is proportional to the cube of the radius of the orbit (including the radius of the planet) and inversely proportional to the mass of the planet

T^2 = 4(π^2)(R^3) / GM

Question 10

State the LAW OF FLOATATION

Answer 10

The weight of a floating body is equal to the weight of the fluid it displaces

Question 11

State the LAW OF RADIOACTIVE DECAY

Answer 11

The activity of a radioactive source is proportional to the number of un-decayed nuclei present

            A = λN

           A = – dN/dt

Question 12

State the LAWS OF REFLECTION

Answer 12

• The incident ray, normal and the reflected ray are all on the same plane
• The angle if reflection is equal to the angle of incidence
— i = r

Question 13

State the LAWS OF REFRACTION

Answer 13

• The incident ray, the normal ray and the refracted ray are all on the same plane
• The ratio of Sin i to Sin r is a constant, n
— n=Sin i / Sin r
— this is also known as SNELL’S LAW

Question 14

State LENZ’S LAW

Answer 14

The direction of induced emf is always such as to oppose the charge causing it

                 E = – dΦ/dt

 — the "–" here signifies that the induced emf opposes the charge

Question 15

State NEWTON’S LAWS OF MOTION

Answer 15

1. ) A body at rest or at a constant velocity will remain at rest or at constant velocity unless acted upon by an external force
2. ) The rate of change of momentum is proportional to the force applied and takes place in the direction of the force.

                                      F = ma

3.) For every action, there is an equal and opposite reaction

Question 16

State NEWTON’S LAW OF UNIVERSAL GRAVITATION

Answer 16

The force of attraction between two point masses is proportional to the product of their masses and inversely proportional the the square of the distances between them

                               F = Gm₁m₂/d²

                                F ∝ m₁m₂/d²

Question 17

State OHM’S LAW

Answer 17

Under constant physical conditions, the proportional difference across a conductor is proportional to the current flowing through it

                                 V = IR

                                  P = VI

Question 18

State the PRINCIPLE OF CONSERVATION OF ENERGY

Answer 18

Energy can neither be created nor destroyed, but can be converted from one form to another

    mgh₁ + ½mu² = mgh₂ + ½mv²

Question 19

State the PRINCIPLE OF CONSERVATION OF MOMENTUM

Answer 19

In any closed system of colliding bodies, the total momentum remains constant