# How do electric circuits work?

Modelling is a useful tool in developing concepts that explain physical phenomena that cannot be directly observed. In this area of study students develop conceptual models to analyse electrical phenomena and undertake practical investigations of circuit components. Concepts of electrical safety are developed through the study of safety
mechanisms and the effect of current on humans. Students apply and critically assess mathematical models during experimental investigations of DC circuits.

Outcome 2
On completion of this unit the student should be able to investigate and apply a basic DC circuit model to simple
battery-operated devices and household electrical systems, apply mathematical models to analyse circuits, and
describe the safe and effective use of electricity by individuals and the community.

### Key knowledge

• apply the concepts of charge (Q), electric current (I), potential difference (V), energy (E) and power (P), in electric circuits;
• analyse electrical circuits using the relationships: I = Q/t, V = E/Q, P = E/t = VI, E = VIt;
• model resistance in series and parallel circuits using:
– potential difference versus current graphs
– resistance as the potential difference to current ratio, including V/I = R = constant for ohmic devices;
– equivalent effective resistance in arrangements in series: RT = R1 + R2 + … + Rn and parallel: 1/RT = 1/R1 + 1/R2 + … + 1/Rn
• model simple electrical devices, car and household (AC) electrical systems as simple direct current (DC) circuits;
• model household electricity connections as a simple circuit comprising fuses, switches, circuit breakers, loads and earth;
• identify causes, effects and treatment of electric shock in homes and relate these to approximate danger thresholds for current and time;
• investigate practically the operation of simple circuits containing resistors, including variable resistors, diodes and other non-ohmic devices;
• convert energy values to kilowatt-hour (kWh);
• evaluate the risk in the use of electrical equipment and power supplies using relevant data;
• identify and apply safe and responsible practices when conducting investigations involving electrical equipment and power supplies.

(Source: vcaa.vic.edu.au)