Electric Circuits An electrical device that provides a path for electric current to flow. Previously, we studied electrostatics, which is the study of charges at rest. Now we’ll begin to focus on electric currents within circuits, which involve charges in motion.

What Things Are Common to All Circuits??? Every circuit must have a continuous path through which electrons may move. Must have a potential difference or voltage to cause the electrons to move. Each circuit should have some circuit loads, such as resistor, to utilize electrical energy. NO load could result in a short circuit.

Circuit Diagrams & Symbols

There are two basic types of circuits: There are two basic types of circuits: One is known as a series circuit which has only one path for the electrons to flow through.

The second type of known as a parallel circuit because there are two or more paths for the electrons to travel through. NOTICE: Three closed loops or circuit ‘branches’.

Which resistors are in Series? Which resistors are in Parallel? B Series: R2, R3 and R4 Parallel: R1 and R3

Electric Current A current (I) exists when charge moves or “flows” through a region. Current is the rate of charge flow past a point in an electric circuit per unit time. The magnitude of the current is measured in amperes (A), where 1 A = 1 C/s.

Conventional Current The direction of conventional current is in the direction in which positive charge flows. In reality, it is the electrons that move. 6.0  6 V I

Switches open and close circuits For electric charge to move, there must be a complete path or closed circuit. Switches open and close circuits

Which switches must be closed for bulb A to light? Which switches must be closed for bulb B to light? Bulb A: Switches a & c Bulb B: Switches a & b

Fuses and Circuit Breakers are two electrical safety devices designed to open the circuit when too much current flows. A short circuit occurs when excessive current overloads a circuit, causing device failure and potentially fire.

Current can change direction Two different types of current : Direct currents (DC) and alternating currents (AC). In a direct circuit, the current flows in only one direction. Ex: Batteries In an alternating current, the direction of the current changes, reversing direction of flow at a particular frequency. Ex: Plugs and outlets

DC vs AC Direct Current Power Source Alternating Current Power Source

As voltage increases, current increases. A potential difference is necessary within a circuit to get electrons to move. Voltage (V): electromotive force or potential difference, usually expressed in volts. As voltage increases, current increases.

Batteries Batteries, known as electrochemical cells or dry cells, are common circuit elements that provide this necessary potential difference, by converting chemical energy into electrical energy. Car Battery- wet cell Rechargeable batteries reverse the process, converting electric to chemical for reuse.

Electric Resistance (R) When charge flows through a circuit, it encounters resistance or opposition to flow. The resistance of a metal conductor is a property which depends upon its dimensions, material and temperature. As resistance increases, current decreases. Resistance is measured in Ohms ().

Ohm’s Law The magnitude of the electric current that flows through a closed circuit depends directly on the voltage and inversely on the circuit resistance. Units: Current (I) Amps Voltage (V) Volts Resistance (R) ohms, 

Using Ohm’s Law i = ? A B C D V = 6 V R = 2  A Simple Circuit

Electrical Power is the rate at which energy is used Electrical Power is the rate at which energy is used. The units for power are J/s or Watt (W). Power (Power) – Watts Voltage (V) – Volts Current (I) – amps Resistance (R) - ohms Power (P) – Watts Work (W) - Joules Time (t) – seconds

Circuit Construction Circuit Construction Simulator: http://phet.colorado.edu/en/simulation/circuit-construction-kit-dc