Electricity(physics)

Unit Electricity

1. Electricity By Rajesh j

2. What is Electricity A type of energy fuelled by the transfer of electrons from negative to positive points within a conductor.

3. Electrical Charge Electric charge is given the symbol Q Electrons are the charge carriers that flow in an electrical circuit from the negative to positive terminals .

4. Charge is measured in Coulombs which is given the symbol C

5. Current An electric current is a rate of flow of electric charge. In electric circuits this charge is often carried by moving electrons in a wire. Denoted with letter “ I “ Units: Amperes (A)

6. Kirchhoff's Current Law The sum of all the currents into a junction is the same as the sum of all the currents out of that junction. Or The algebraic sum of all the currents entering and leaving a node is equal to zero

7. Voltage Energy applied per unit charge is called voltage. V = Where V = Voltage in Volts E = Energy applied by source ( ex: battery) in Joules Q = Total Charge in Coulomb  

8. Kirchhoff's Voltage Law The sum of input voltage is equal to sum of voltage drops in a loop. or Th e algebraic sum of all the voltages in a loop is equal to zero.

9. Circuit Symbols

10. Electrical Circuits

11. Different types of circuit There are different ways in which you can connect cells and components (such as lamps ) to create a circuit: series parallel combination of both

12. Series Circuit A series circuit has only one electrical path. You can trace from one side of the battery to the other, through each component, without lifting your finger from the page.

13. Current and Voltage in Series Current remains same in series circuit. Voltage gets divided.

14. Question: Build a series circuit which contains a 6V battery pack, three 2 V lamps in lamp holders, and a meter used for measuring current. What is the meter called? Where is it positioned in the circuit?

15. Quiz What is a series circuit? What is the symbol for current? What are the units of current? What is the relationship between current and time ? What do we know about the current in a series circuit ? How do we measure current? Draw the symbol for this. Describe how to measure current in a series circuit .

16. Parallel Circuit In a  parallel circuit , all components are connected across each other, forming exactly two sets of electrically common points.

17. Current and Voltage in Parallel Voltage remains same in parallel circuit. Current gets divided.

18. Question: Build a parallel circuit which contains a 6V battery pack, three 6V lamps in lamp holders, and a meter used for measuring total current and to measure the voltage across each lamp What is the meter called to measure voltage? Where is it positioned in the circuit?

19. Quiz What is a parallel circuit? What is the symbol for voltage? What are the units of voltage? What do we know about the voltage in a parallel circuit ? How do we measure voltage? Draw the symbol for that measuring instrument. Describe how to measure voltage in a parallel circuit.

20. Combination of Series & Parallel

21. Resistance Electrical  resistance , the measure of the degree to which a conductor opposes an electric current through that conductor Resistance is denoted with R Units: ohms Ω

22. Resistivity of Some Materials

23. Ohm’s Law The potential difference (voltage) across an ideal conductor is proportional to the current through it. The constant of proportionality is called the "resistance", R. Ohm's Law  is given by: V = I R ( where V is the potential difference between two points which include a resistance R) . Therefore, R =  

24. Ohmic Resistors Ohmic resistors  are those  resistors  that have a constant resistance. In other words, the follow the Ohm's law. If you take such a  resistor , apply voltage across it, whilst measuring current and voltage, and then draw a graph of current versus voltage, you get a straight line Example: wire Note: Many electrical  components   in today's electronics do not follow Ohm's law.

25. Non- Ohmic Resistors Non- Ohmic Resistors gives a curve with an increasing gradient. It shows that the resistance  increases as the current increases .

26. Examples of Non Ohmic Resistors Filament Bulb

27. Examples of Non Ohmic Resistors A diode only allows current to flow in one direction through it (forward biased), when the current tries to flow the other way (reverse biased) no current is allowed to flow through the diode.  Diode

28. Examples of Non Ohmic Resistors The resistance of a thermistor decreases as it’s temperature increases .  the thermistor is used in circuits which monitor and control the temperature of rooms, freezers & fridges etc. Thermistor

29. Examples of Non Ohmic Resistors The resistance of an LDR  decreases as the light intensity falling on it  increases . LDR’s are used in circuits which automatically switch on lights when it gets dark, for example street lighting.  LDR (light dependent resistor)

30. Super Conductors A superconductor is a material that can conduct electricity with no resistance once they are cooled to a temperature called the transition temperature T c . For Example : Transition Temperature for 1. Mercury is 4 Kelvin 2. Calcium is 254 Kelvin Application: maglev trains, magnetic resonance imaging (MRI)

31. Applications of Super Conductor Most train magnets are also electromagnets, often using liquid nitrogen-cooled superconductors to lower the energy required to create such large fields Magnets made from rare-earth elements , however, produce a stronger magnetic field than ferrite (iron compounds) or alnico (alloys of iron, aluminium, nickel, cobalt, and copper) magnets to lift and guide the train cars over a guideway. Maglev Train

32. Applications of Super Conductor MRI

33. Equivalent Resistance

34. Problems from the text book pg no:49

35. Electronic Circuits and Devices Voltage Divider A  voltage divider  is a simple circuit which turns a large  voltage  into a smaller one.

36. Problem from text book pg 53

37. Capacitors A capacitor (originally known as a condenser ) is an electrical component used to store energy electrostatically in an electric field . It contains two electrical conductors (plates) separated by a dielectric (i.e., insulator ). Applications: DC blocking capacitor Capacitor as a filter : Low pass filter and High pass filter

38. Capacitance (not in syllabus) Note : Permittivity of Vacuum is 8.85 x 10 -12  farad per meter (F/m)

39. Diode A diode is a specialized electronic component with two electrodes called the anode and the cathode . Most diodes are made with semiconductor materials such as silicon, germanium , or selenium. The fundamental property of a diode is its tendency to conduct electric current in only one direction . Note : If Anode of Diode is connected to anode and Cathode of Diode is connected to cathode of Voltage source respectively, then diode is said to be Forward biased i.e acts as ON Switch. But, If reverse polarities connected called Reverse biased i.e acts a OFF Switch

40. Applications of Diode Half Wave Rectifier:

41. Applications of Diode Full Wave Rectifier [type 1]

42. Applications of Diode Full Wave Rectifier [type 2]

43. Problems based on KCL, KVL and Ohm’s Law Required : Kirchhoff’s Laws, Ohm’s Law and Simultaneous Equations (Maths)

44. Problems based on KCL, KVL and Ohm’s Law Find current in each resistor.

45. Problems based on KCL, KVL and Ohm’s Law If B 1 = 20 volts, B 2 = 10 volts; R 1, R 3, R 5 = 5 ohms; and R 2, R 4 = 2 ohms. Find current in each resistors.

46. Problems based on KCL, KVL and Ohm’s Law Find the current flowing through R 5 with proper direction.

47. Problems based on equivalent resistance

48. Problems based on equivalent resistance

49. Problems based on equivalent resistance

50. Problems based on equivalent resistance

51. Logic Gates (Not in Syllabus)

52. Truth Table

53. Two Way Switch

54. Static Electricity When two objects are rubbed together to create static electricity O ne object gives up electrons and becomes more positively charged while the other material collects electrons and becomes more negatively charged . This is because one material has weakly bound electrons, and the other has many vacancies in its outer electron shells. One common example of this would be shuffling your feet across carpet.

55. Electricity Completed

56. Next Chapter: Electromagnetism

57. Bibliography http://physicsnet.co.uk/gcse-physics/non-ohmic-devices / http:// whatis.techtarget.com/definition/diode http://www.ee.surrey.ac.uk/Projects/CAL/digital-logic/gatesfunc /