Introduction to Electronics Basic Components and Circuits

Terminology and Assignments Complete students Handout 1+2: Electrical Components and Circuits Terminology Complete Student Handout 3: Ohm’s Law Problems Complete Student Handout 4: Ohm’s Law Story Problems Complete Student Handout 5: Circuits Story Problems Complete Electrical Breadboard Experiments

Common Electrical Components and Symbols Battery

Circuit Representation of Ohm’s Law Definition: Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points Current (I) = Voltage (V) / Resistance (R) Units Current = Amps Voltage = Volts Resistance = Ohm’s Circuit Representation of Ohm’s Law

Electrical Circuits Electric charge: Volts 2.4 Electrical Circuits Electric charge: Volts an amount of electrical energy can be positive or negative Electric current: Amperes (Amp) a flow of electrical charge, often a flow of electrons conventional current is in the opposite direction to a flow of electrons Current flow in a circuit a sustained current needs a complete circuit also requires a stimulus to cause the charge to flow

Power Electric power, like mechanical power, is the rate of doing work, measured in watts, and represented by the letter P. The term wattage is used colloquially to mean "electric power in watts." The electric power in watts produced by an electric current I consisting of a charge of Q coulombs every t seconds passing through an electric potential (voltage) difference of V is P (watts) = work done per unit of time P = voltage (V) * electrical charge (Q)/ time (seconds) P = voltage (V)* electrical current (I)(amps) P = VQ/t = VI

Circuits Definition: An electrical network/circuit is flowing from positive to negative (also known as from high voltage to low voltage) just like water flows from regions of high pressure to regions of low pressure. Circuits are an interconnection of electrical components (e.g. batteries, resistors, inductors, capacitors, switches) or a model of such an interconnection, consisting of electrical elements (e.g. voltage sources, current sources, resistances, inductances, capacitances) creating a closed loops, giving a return path for the current.

Electrical circuits are a lot like (water) plumbing systems in which water circulates (except discharging of water outside of the closed piping system is not allowed). A battery can push electrical current through a circuit (which is a continuous connection of wires and components) just as a water pump can push water through a closed plumbing system.

One needs to have a “complete circuit” for current to flow (out of the + end of the battery, through the wires and components, then back into the – end of the battery) just as one needs a closed network of pipes for a plumbing system to be able to circulate water from the pump, through the pipes, then back to the pump again.

In-Series Circuit Components connected in series are connected along a single path, so the same current flows through all of the components. the current through each of the components is the same, and the voltage across the circuit is the sum of the voltages across each component. In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents through each component.

In- Series Circuit

Parallel Circuit If two or more components are connected in parallel they have the same potential difference (voltage) across their ends. The potential differences across the components are the same in magnitude, and they also have identical polarities. The same voltage is applicable to all circuit components connected in parallel. The total current is the sum of the currents through the individual components, in accordance with Kirchhoff’s current law.

Sample Parallel Circuits

In terms of (water) plumbing, a water heater would be in series with a room hot-water radiator – the water flows through the water heater then the exact same water molecules go on to the radiator. On the other hand, two hot-water room radiators might be plumbed in parallel – the water would choose to go either to the living room radiator or to the bedroom radiator before returning to the water heater, but no single water molecule would go through both radiators in 1 trip.

Resistors in Series and Parallel R = R1 + R2 + R3 Parallel

Kirchhoff’s Laws Kirchhoff’s Current Law At any node (junction) in an electrical circuit, the sum of the currents flowing into that node is equal to the sum of currents flowing out of that node Or The sum of currents in a network of conductors meeting at a point is zero Kirchhoff’s Voltage Law The directed sum of the electrical potential differences (voltage) around any closed network is zero The sum of the electro magnetic force in any closed loop is equivalent to the sum of the potential drops in that loop. The algebraic sum of the products of the resistance of the conductors and the currents in them in a closed loop is equal to the total electromagnetic force available in the loop The current entering any junction is equal to the current leaving that junction. i2 + i3 = i1 + i4 The sum of all the voltages around the loop is equal to zero. v1 + v2 + v3 - v4 = 0

Kirchhoff’s Current Law At any instant the algebraic sum of the currents flowing into any junction in a circuit is zero For example I1 – I2 – I3 = 0 I2 = I1 – I3 = 10 – 3 = 7 A

Kirchhoff’s Voltage Law At any instant the algebraic sum of the voltages around any loop in a circuit is zero For example E – V1 – V2 = 0 V1 = E – V2 = 12 – 7 = 5 V