EJC Physics H214 Current of Electricity - 1. Notes-2023 (Full)

One of William Gilbert’s (1544 - 1603) contribution to the field of science was his study on static electricity. He established the “amber effect” (now called the triboelectric effect) – that certain materials such as amber can become electrically charged by friction with other materials. As Amber is called elektron in Greek, and electrum in Latin, Gilbert decided to refer to the phenomenon by the adjective “electricus”, giving birth to the word “electricity”. Content • Electric current • Potential difference • Resistance and resistivity • Electromotive force Learning Objectives: Candidates should be able to: (a) show an understanding that electric current is the rate of flow of charge (b) derive and use the equation I = nAvq for a current-carrying conductor, where n is the number density of charge carriers and v is the drift velocity (c) recall and solve problems using the equation Q = It (d) recall and solve problems using the equation V = W /Q (e) recall and solve problems using the equations P = VI, P = I2R and P = V2 / R (f) define the resistance of a circuit component as the ratio of the potential difference across the component to the current passing through it and solve problems using the equation V = IR (g) sketch and explain the I–V characteristics of various electrical components such as an ohmic resistor, a semiconductor diode, a filament lamp and a negative temperature coefficient (NTC) thermistor (h) sketch the resistance-temperature characteristic of an NTC thermistor (i) recall and solve problems using the equation R =ρl/A (j) distinguish between electromotive force (e.m.f.) and potential difference (p.d.) using energy considerations (k) show an understanding of the effects of the internal resistance of a source of e.m.f. on the terminal potential difference and output power.

Previously from oscillations through waves, w e used a simplified microscopic model of individual particles oscillating and linked them to the macroscopic behaviour of wave properties. The study of the large-scale behaviour saves us the effort of having to model all of the individual behaviour of particles, and allows u s to investigate interactions and changes, such as multiple waves meeting and overlapping with each other. Here we study the macroscopic behaviour of electrons flowing through components and wires. When an electrical conductor is conducting electricity, an electric current is said to flow through it. This current is made up of a net flow of charged carriers (or charged particles) such as electrons ( negatively charged ), protons (positively charged) or ions (either polarities). Unless specified, conventional flow is assumed when working with current flow. Current is a scalar quantity; it does not obey vector addition laws. Electric current I is one of the 7 base S.I. quantities and has the S.I. unit of Ampere (A). It is chosen as a base quantity because it is easier to define the u