1. Delivered by Mr. Rajitha de Silva Courtesy Ms. Shashika Lokuliyana

3.  A path intended for converting electrical energy into other forms…  It includes; 1. A source EMF 2. A load 3. Connecting conductors 4. And usually a Control Device (Switch)

4.  Any Transducer that is capable of producing an electro-motive force (voltage). Generator Alternator Battery Photo Cell

5.  The voltage between two points is the cost in energy (work done) required to move a unit of positive charge from the more negative point (lower potential) to the more positive point (higher potential).  Voltage is also called potential difference or electromotive force (EMF).  The unit of measure : volt (V).

7.  A direct current (dc) is a current that remains constant with time.  An alternating current (ac) is a current that varies sinusoidally with time.

8. Battery (E)y Resistor (R)

9. Battery (E)y Resistor (R) V Point APoint B

10. Battery (E)y Resistor (R) A

11. Battery (E)y Resistor (R) e

12. Battery (E)y Resistor (R)

14. Circuit elements can absorb or release power (I.e. From or to the rest of the circuit); power can be a function of time. How to keep the signals straight for absorbing and releasing power?

15.  Associated reference directions refers to defining the current through a circuit element as positive when entering the terminal associated with the + reference for voltage.

16.  Usually power is converted in to what type of energy?  Heat (most of the time)  Mechanical work (motors)  Radiated energy ( lamps, transmitters)  Stored energy (batteries capacitors)  Name one device that you use which converts many kilowatts of electrical energy to heat.  Computer (PC/Laptop)  Mobile phone

18. The resistance of a material is the property to resist the flow of electrons when an external electric field is applied. The resistance converts the applied energy into heat much like the mechanical friction due to colliding electrons and collisions between electrons and other atoms. The unit of Resistance is known as Ohms ( Ω )

20. Fixed resistors Variable resistors

22. Ohm’s Law Ohm’s Law states that the current through an electric path is dependent on the resistance of the path.

23.  Resistors are also characterized by;  How much power they can safely dissipate  Tolerance (accuracy)  Temperature coefficient  Noise  Voltage coefficient ( the extent to which R depends on applied V)  Stability with time  Inductance, etc..  What is the most commonly used power level of resistors? ¼ watts

28. Shortcut no. 1 A large resistor in series with a small resistor has the resistance of the larger one, roughly. Shortcut no. 2 A large resistor in parallel with a small resistor has the resistance of the smaller one, roughly. Shortcut no. 3 A 5k and 10k resistor in parallel is equal to three 10k ( two 10k resistors in parallel is 5k) resistors in parallel, which gives the resistance 3.33k. Because the resistance of n equal resistors in parallel is 1/n th the resistance of the individual resistors

30. Show that it is not possible to exceed the power rating of a ¼ watt resistor of resistance greater than 1k, no matter how you connect it, in a circuit operating from a 15 volt battery.

32. What are dependent and independent Voltage or Current sources? What are the symbols used for dependent and independent Voltage or Current source representations?

35.  The sum of the currents entering any junction must equal the sum of the currents leaving that junction. (KCL) (Conservation of charge)  The algebraic sum of the changes in potential across all of the elements around any closed circuit loop must be zero. (KVL) (Conservation of energy)

36. Kirchhoff’s voltage law (KVL) states that the algebraic sum of the potential rises and drops around a closed loop (or path) is zero.

38. Find the current which flows through R4.

40. Kirchoff’s Current Law (KCL) states that the algebraic sum of the currents entering and leaving an area, system, or junction is zero.

44.  In a Series Circuit, the Voltage across resistances divide according to the magnitude of the resistances.  Consider a Series circuit with two elements R1 and R2 and the total voltage applied across them is V. Let the current flowing through each of the two elements (series) be “I”.

48. The current in parallel circuit elements divide in ratios according to the inverse of their resistor values. Consider two parallel elements R1 and R2 and a total current I.

57. An Open circuit is one which have voltage across it but current through it is zero. An open circuit is represented by infinite resistance.

58. A short circuit is one which allow current through it but voltage across it is zero. A short circuit is represented by zero resistance.