# About this site – Learn Physics online

This website (Mini Physics) offers O and A Level physics revision notes for you to learn Physics online. O Level is equivalent to American High School Diploma and A Level is equivalent to Advanced Placement. If you spot any mistakes in my explanation, please email the site administrator at miniphysics@hotmail.com with the relevant web address and […]

### SS: Ray Diagrams For Converging Lens

Trick to drawing ray diagrams for converging lens: There is one ray of light passing through the center of the lens. Always. 2 rays are enough to determine the position of image/object. The other ray of light ALWAYS passes through the focal point of the lens. Either the first focal point of the second focal […]

### Derivation of geodesic deviation equation

Question: Let $x^{a}$ be a geodesic, and $x^{a} + \epsilon^{a}$ be a neighbouring geodesic such that $\epsilon^{a}$ is infinitesimal. Prove the so-called geodesic deviation equation: $\frac{D^{2} \epsilon^{a}}{D \tau^{2}} = \, – R^{a}_{\: bcd} \epsilon^{c} \frac{dx^{b}}{d \tau} \frac{dx^{d}}{d \tau}$ Relevant Geodesic equations: $\frac{d^{2} x^{a}}{d \tau^{2}} + \Gamma^{a}_{\: bc} \frac{dx^{b}}{d \tau} \frac{d x^{c}}{d \tau} = 0$ […]

### Should I study physics in university?

Am I suitable to study physics in university? Should I study physics in the university? What can I expect to encounter as a physics major? How is physics in the university like? I am sure these questions are on the mind of any potential physics undergraduate. This post is meant to give you a rough […]

### Power

Power is defined as the rate of work done or energy converted with respect to time. $P = \frac{W}{t}$ OR $P = \frac{E}{t}$, where W = work, t = time, E = Energy SI Unit for power is watt (W), scalar quantity Another useful equation for power: P = Fv, where F = force, v = […]

### Energy

Energy of a system is defined as its capacity to do work. SI unit : joules (J) Scalar Quantity Energy can be converted from one form to another. It can also be transferred from one body to another through work done and/or heat exchanges. The Principle of conservation of energy states that energy cannot […]

### Work

Work is done when a force moves the object in the direction of the force and is given by the product of the force and the distance moved in the direction. W = Fs , Where W= Work, F = Constant Force (N), S = Distance moved in the direction of the force (m) SI Unit for work […]