Entries by Orodruin

A Physics Misconception with Gauss’ Law

Introduction It is relatively common to see the following type of argument: The surface area is ##A## and the enclosed charge is ##Q##. The electric field strength on the surface is therefore ##E = Q/\varepsilon_0 A##. The problem is that this statement is only true in very special cases. In this Insight, we discuss the…

How Can We Jump When the Ground Does No Work?

It is relatively common on Physics Forums to see arguments that are effectively similar to the following: When we jump off the ground, the ground does not move. Because of this, the force from the ground on us does zero total work. Since the force does no work, we cannot gain any kinetic energy. We…

Symmetry Arguments and the Infinite Wire with a Current

Many people reading this will be familiar with symmetry arguments related to the use of Gauss law. Finding the electric field around a spherically symmetric charge distribution or around an infinite wire carrying a charge per unit length are standard examples. This Insight explores similar arguments for the magnetic field around an infinite wire carrying…

Learn the Basics of Dimensional Analysis

As a university teacher and as a PF member, I have often noted that students are largely unaware of or not using dimensional analysis to help them in their pursuit of knowledge or to check their results. A number of recent threads on PF have also highlighted this issue. The intent of this Insight is…

Plus/minus What? How to Interpret Error Bars

People sometimes find themselves staring at a number with a ± in it when a new physics result is presented. But what does it mean? The aim of this Insight is to give a fast overview of how physicists (and other scientists) tend to present their results in terms of statistics and measurement errors. If…