Unit 2 | Using tools, equipment and other devices Lecturer: Mr. Jerome Smith Course: CAP

Basic Electric Circuits & Components Introduction SI Units and Common Prefixes Electrical Circuits Direct Currents and Alternating Currents Resistors, Capacitors Ohm’s, Power Law Power Dissipation in Resistors Resistors in Series and Parallel Resistive Potential Dividers Sinusoidal Quantities Circuit Symbols

SI Units Quantity Quantity symbol Unit Unit symbol Capacitance C Farad Charge Q Coulomb Current I Ampere A Electromotive force E Volt V Frequency f Hertz Hz Inductance (self) L Henry H Period T Second s Potential difference Power P Watt W Resistance R Ohm Ω Temperature Kelvin K Time t

Common Prefixes Prefix Name Meaning (multiply by) T tera 1012 G giga 109 M mega 106 k kilo 103 m milli 10-3  micro 10-6 n nano 10-9 p pico 10-12

Electrical Circuits Electric charge Electric current an amount of electrical energy can be positive or negative Electric current 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

Section 7.2: Electric Current Static Electricity: build up of charges that pass QUICKLY to another object Electric Current: continuous flow of charges through a conductor

Electromotive force and potential difference the stimulus that causes a current to flow is an e.m.f. this represents the energy introduced into the circuit by a battery or generator this results in an electric potential at each point in the circuit between any two points in the circuit there may exist a potential difference both e.m.f. and potential difference are measured in volts

A simple circuit A water-based analogy

Voltage Voltage is created by a chemical cell (battery) when it changes chemical energy to electrical energy by a generator when it changes mechanical energy to electrical energy by a solar cell when it changes light energy to electrical energy.

Direct Current and Alternating Current Currents in electrical circuits may be constant or may vary with time When currents vary with time they may be unidirectional or alternating When the current flowing in a conductor always flows in the same direction this is direct current (DC) When the direction of the current periodically changes this is alternating current (AC)

Resistors, Capacitors and Inductors Resistors provide resistance they oppose the flow of electricity measured in Ohms () Capacitors provide capacitance they store energy in an electric field measured in Farads (F) Forumlae: Capacitors in Series: (1/CTOTAL) = (1/C1) + (1/C2) + (1/C3) Capacitors in parallel: CTOTAL = C1 + C2 + C3 ..... Inductors provide inductance they store energy in a magnetic field measured in Henry (H)

Check for Understanding What is voltage? How is voltage generated? (3 ways) What is current?

Resistance Resistance: the tendency for a material to oppose the flow of electrons Changes electrical energy into thermal energy and light Ex: lightbulb filament Resistance is measured in Ohms (Ω)

What Affects Resistance?

Household Circuits: Fuse: a small piece of metal that melts if the current becomes too high Circuit Breaker: contains a small piece of metal that bends when it gets hot bending causes a switch to flip and opens the circuit

Ohm’s Law The current flowing in a conductor is directly proportional to the applied voltage V and inversely proportional to its resistance R V = IR I = V/R R = V/I

Power Law Power is the measure of how much work can be done in a given amount of time. Did you know? 1. W = V x I 2. W = I2 x R ? 3. W = V2 / R ? Lets see!!

Sinusoidal Quantities Length of time between corresponding points in successive cycles is the period T Number of cycles per second is the frequency f f = 1/T

Circuit Symbols

Key Points

Let’s Compare Series and Parallel Circuits Series Circuits Parallel Circuits _______ path(s) for current Current ________________ Voltage ________________ Break in circuit _______________________ Adding resistance in series ______________________ _______ path(s) for current Current ________________ Voltage ________________ Break in circuit _______________________ Adding resistance in parallel _______________________

Let’s Compare Series and Parallel Circuits Series Circuits Parallel Circuits 1 path(s) for current Current is the same at every point Voltage drops at each resistor Break in circuit stops all current Adding resistance in series decreases total current (dimmer light bulbs) multiple path(s) for current Current can be different in each branch Voltage same across each resistance Break in circuit does not affect other bulbs Adding resistance in parallel increases total current