1. Pg 31-60 HUGHES Electrical & Electronic Technology
Simple dc circuit
Pg 31-60
HUGHES
Electrical & Electronic Technology

2. What is circuit? A complete connection of a source and a load
Source : voltage source, current source such as battery
Load : resistor, capacitor, inductor

3. What is network?
A network is a combination of several circuits

4. Series circuit
therefore

5. therefore
In general for n series of resistor, Rt

6. Example 1
One man decides to connect two lamps of in series in order to get more light . However he found the lamps give out very litter light. Why? Can you explain this.
To get full light , we must connect a single lamp to 220V source , thus we have
When connect two lamps in series , then
Since the current is less then the lamp cannot give light fully.

7. Example 2
Calculate the voltage across each of resistors as in figure and hence calculate the supply voltage V

8. Example 3
Calculate the circuit’s current

9. Voltage divider

10. Example 4
Given that R2=100W, calculate R1 in order to obtain an output voltage 10V across R2

11. Parallel circuit
but
then

12. then
In general

13. Current divider
But
and
Therefore

14. Example 5
Calculate I1,I2 and I3

15. Example 6 Calculate the effective resistance and the power supply
Hence

16. Example 7 Calculate the current in the 2 W resistor, given that
R1 =2 W
R1 =4 W
I1 = I - I2 = = 4A
I1 and I2 are equal
I1 and I2 are not equal

17. Kirchoff’s laws
Current Law- At any instant the algebraic sum of the currents at a junction in a network is zero

18. Example 8
Determine the relationship between the currents I1 ,I2, I4 and I5.
At junction a
Hence
At junction b
Therefore
Then or

19. Example 9 Given that I1=2.5A and I2=-1.5A. Calculate the current I3.
From Kirchoff’s law

20. Example 10 Determine the current I2, I4 and I5. At junction a
At junction b
At junction c

21. Example 11 Determine the current I1 and I2.
Use current divider concept a
At junction a

22. Voltage Kirchoff’s law
Total potential difference across connected components in a complete circuit is zero. The sign of potential difference (p.d) of the source (or e.m.f) is always in opposite sign of the passive components of the circuit or
thus

23. With many sources of e.m.f

24. Example 12 Determine the Voltage V1 and V3. Loop A To check the result
Loop B
Loop C

25. Example 13 Calculate VAB for the network shown Branch A Branch B
Applying Kirchoff’s law

26. Example 14 Calculate V1 and the e.m.f E2 Kirchoff’s law to left loop
Kirchoff’s law to right loop
To check again for outside loop