1. Sinai University Faculty of Engineering Science Department of Basic Science 10/9/20151 w3

2. Chapter 1-2 Electrodynamics 10/9/20152 w3

3. Electric potential But since the electric field is a force per unit charge, the electric potential must be energy per unit charge. E=Force/charge N/C V=Energy/Charge J/C (Volts) The electrical potential is defined as the work performed when moving an electric charge q between infinity and a potential level, divided by that charge. Whereas the electrical potential difference is defined as the work performed when moving an electric charge q between two potential levels, divided by that charge. 10/9/20153 w3

4. Electric potential energy, U V c =U t c /q t. J/C(=Volt) U t c = q t V c. CV(=J) Electric potential energy = q t E L in uniform electric field, E = q t E L in uniform electric field, E A new energy unit in atomic and nuclear scale 1eV= 1.6x10 -19 CX1 V=1.6x10 -19 J 10/9/20154 w3

5. Example A fresh flashlight battery has a potential difference of about 1.5 Volts between its terminals regardless of what their absolute potentials really are. If an electron were allowed to move from the negative terminal of such a battery to the positive one it would gain a kinetic energy of 1.5 electron Volts but its potential would drop by 1.5 Volts. 10/9/20155 w3

6. Example The potential energy has been converted to kinetic. If we wanted to move the electron back to the negative electrode we would have to perform work of 1.5 electron Volts because we would be moving the electron against the repelling force of excess electrons residing in the negative terminal. 10/9/20156 w3

7. Electric current An electric current is a flow of charged particles. Current is measured using an ammeter. The unit of current is the Ampere, A. 10/9/2015 7 I av =nAv d q,

8. Electric potential +ve charges  V=1.5 V  W=q  V  W= KE 10/9/20158 w3

9. Electric Charges,  Q ++++++ F E 10/9/20159 w3

10. Electric current No electric Field There is an electric Field 10/9/201510 w3

11. Ideal Current Source An ideal current source is defined as having the ability to force its nominal current into any load. R in is to be infinite An approximation to an ideal current source is a battery of very high voltage V in series with a very large resistance R. Such approximation would supply a current V/R into any load that has a resistance much smaller than R. 10/9/201511 w3

12. Ideal Voltage Source Ideal Voltage Source The ideal voltage source is defined to have the nominal potential difference between its terminals and a zero internal resistance. the nominal potential difference between its terminals and a zero internal resistance. A voltage source must be able to maintain an excess electron density on one electrode and an equal but opposite rarefaction on the other, regardless of how many electrons may be leaving any one terminal. In terms of the microscopic events we can define the voltage source as a device which can withdraw electrons from one of its terminals and deposit them onto the other. This can be done by mechanical means as in a generator or by chemical means as in a battery. 10/9/201512 w3

13. Electric resistance Measures the relative ease with which a current flows in a medium. 10/9/201513 w3

14. Electrical Resistivity,  10/9/201514 w3

15. Sample Problem 1 ( b) The area of a rectangular face is (1.2 x 10 -2 m)x(0.15 m) or 1.80 x l0 -3 m 2. From Eq. 1-6 A rectangular block of iron has dimensions 1.2 cm x 1.2 cm x 15 cm. (a) What is the resistance of the block measured between the two square ends? (b) What is the resist­ance between two opposing rectangular faces? The resistivity of iron at room temperature is 9.68 x 10 -8 m. 0.15 m 1.2x10 -2 m Solution (a) The area of a square end is (1.2 x 10 -2 m) 2 or 1.44 x 10 -4 m 2. From Eq. 1-6, 10/9/201515 w3

16. Ohmic Resistance A conducting device obeys Ohm's law if the resistance between any pair of points is independent of the magnitude and polarity of the applied potential difference. 10/9/201516 w3

17. Electric circuit components 10/9/201517 w3

18. 1-Draw a loop inside the simple circuit, and specify a certain direction in such loops. 2- Follow the following sign convention, a- The current is positive if it is in the same direction of the loop direction. a- The current is positive if it is in the same direction of the loop direction. b- The emf, e, is positive if its direction, from negative to its positive pole, is in the same direction of the loop direction. b- The emf, e, is positive if its direction, from negative to its positive pole, is in the same direction of the loop direction. 3- Make an equation for each simple loop. 6- Solve these equations simultaneously to obtain circuits unknown 7- If you get any current with negative sign, this means that the direction of this current is opposite to that considered in step 3, but its value is correct. The rules for solving simple circuits 10/9/201518 w3

19. Example +- +  r R 10/9/201519 w3

20. Example R  ,r 1  ,r 2 i a bc 10/9/201520 w3

21. Power in DC Circuits P= =IV Energy conversion 95% into light 10/9/201521 w3

22. Types of Electric Currents The current we have considered so far is called a D.C. (Direct Current) since its direction does not change with time. An A.C. (Alternating Current) is one in which the current changes direction with time, and hence its sign, with some fixed frequency. Time V volt OR I ampere 10/9/201522 w3

23. Assignment Artificial Electrical pacemaker Structure, theory of operation, uses 10/9/2015 w3 23

24. Capacitor Storing Electrical Energy A device that stores electrical energy based on opposite charges is called a capacitor. C=   A/d d A  E 10/9/201524 w3

25. Charge and Discharge of a Capacitor,Pacemakers 10/9/2015 w3 25

26. Circuit Topology R eq = R 1 + R 2 SERIES PARALLEL NOT SERIES Neither PARALLEL 10/9/201526 w3

27. Home work Solve the following problems 2,4,6,11,15,16 20, 24, 25,36,39 Hand it next week Mhmd_sa3d@yahoo.com 10/9/201527 w3

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