1. Current,Voltage and Resistance
Electric Circuits – DDPE 1102
By: Norulhusna Ahmad

2. Voltage
If a free electron leaves the vicinity of the parent atom, regions of positive and negative charge have been established
Every source of voltage is established by simply creating a separation of positive and negative charges
The more the required voltage, the greater the quantity of positive and negative charge

3. FIGURE 2-2 The atomic structure of copper.
Robert L. Boylestad Essentials of Circuit Analysis
Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

4. FIGURE 2-4 Defining the positive ion.
Robert L. Boylestad Essentials of Circuit Analysis
Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

5. Voltage
One coulomb of charge is defined as the total charge associated with X 1018 electrons
If a total of 1 Joule (J) of energy is used to move the negative charge of 1 coulomb (C) there is a difference of 1 volt (V) between the two points

6. FIGURE 2-5 Defining the voltage between two points.
Robert L. Boylestad Essentials of Circuit Analysis
Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

7. Voltage V=Voltage [volts (V)] W= Energy [Joules (J)]
Q= Charge [Columbs (C)]

8. Example
Find the voltage between two points if 60J of energy are required to move a charge of 20C between two points.
Determine the energy expanded moving a charge of 50μC between two points if the voltage between the points is 6V.

9. Voltage
There are a variety of ways to separate charge to establish the desired voltage:
chemical action - batteries
mechanical methods - generators
alternative sources - solar cells
Voltage is always defined as the potential difference between two points (one of those points may be ground)

10. Current
In any conductor, free electrons generated at room temperature are in constant motion in random directions (the net flow in any one direction is zero)
If a voltage is applied across the conductor, electrons will be forced to move toward the positive terminal

11. Current
If X 1018 electrons pass through an imaginary plane in one second, the flow of charge or current is said to be 1 ampere (A)

12. Current
Even small levels of current through the human body can be dangerous
currents through the body, in excess of 10 mA should be considered dangerous
currents of 50 mA can cause severe shock
currents in excess of 100 mA can be fatal
Unless it is wet or broken, due to an injury, the skin usually has enough resistance to limit current through the body to safe levels for voltage levels found around the home

13. FIGURE Motion of negatively charged electrons in a copper wire when placed across battery terminals with a difference in potential of V volts.
Robert L. Boylestad Essentials of Circuit Analysis
Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

14. FIGURE 2-9 Basic electric circuit.
Robert L. Boylestad Essentials of Circuit Analysis
Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

15. Currents I=currents [Amperes (A)] Q=charges [Coulombs (C)]
t= time [Seconds (s)]

16. Example
The charge flowing through the imaginary surface of Fig is 0.16C every 64ms. Determine the current in amperes.
Determine how long it will take 4x1016 electrons to pass through the imaginary surface of Fig.2.9 if the current is 5mA.

17. Voltage Sources
An electromotive force (emf) is a force that establishes the flow of charge (or current) in a system due to the application of a difference in potential

18. Ammeters and Voltmeters
Voltmeters measure potential difference between two points
in volts, millivolts, microvolts, kilovolts
potential difference is measured by connecting the meter across two points

19. Ammeters and Voltmeters
Ammeters measure current levels
in amps, milliamps, microamps
must be placed in the network such that the charge will flow through the meter (circuit must be opened and meter placed between resulting terminals)

20. Resistance
The resistance of any material is due primarily to four factors:
Material resistivity (ρ)
Length (l)
Cross-sectional area (A)
Temperature of the material

21. Resistance 1 mil = 1/1000 in or 1000 mil=1 in
The area of the wire with a diameter of 1 mil has an area of 1CM
However, the clear relationship is

22. FIGURE 3-5 Verification of Eq. (3.2): ACM = (dmils)2.
Robert L. Boylestad Essentials of Circuit Analysis
Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

23. Types of Resistors
Today, the most common fixed type resistors are metal film resistors
resistance is achieved by depositing a thin metal film on a ceramic rod, then trimming the metal film in a helical manner to establish resistance

24. Types of Resistors
For a particular manufacturer, and style, the size of a resistor will increase with the power or wattage rating
The size of a resistor does not define its resistance level

25. Types of Resistors
Variable resistors are referred to as rheostats (if used as a variable resistor) or potentiometers (if used for controlling potential levels)
a contact is moved along a resistive element

26. Resistor Color Coding
First two bands represent the first and second digits, respectively
Third band determines the power-of-ten multiplier for the first two digits
Fourth band is the manufacturer’s tolerance

28. Conductance
The measurement on how well the material will conduct electricity is called conductance
A resistance of 1MΩis equivalent to 10-6 S.
The larger the conductance, the less the resistance and the greater the conductivity.

29. Examples
How much energy does a 10V battery in your car use to move 2.89x1019 electrons through the electrical circuit?
How many electrons pass through a conductor in 1 min and 15 sec if the current is 4 mA?
What is the resistance of copper wire 200 ft long and inch on diameter? (ρ=10.37)
What is the diameter in inch of an aluminum conductor that is 80ft long with a conductance of 0.4S? (ρ=17)

30. Exercise Listed are three conductance of different materials
Silver (ρ=9.9): 1 ft long with diameter of 1mil
Copper (ρ=10.37): 10 ft long with diameter of 10 mils
Aluminum (ρ=17): 50 ft long with diameter of 50 mils
Without working out the numerical solution, which do you think has the most resistance? Explain
Find the resistance of each section and compare your answer with the result above

31. Activity
In your group, create your own analogy to remember the colour code of resistor and must be agreed by all of the group member.
Explain the relationship between voltage, current and resistance in the way of electron movement in analogy form.
All the discussion must be fill into your file and will be useful when I tested you in QUIZ.