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

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

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

Series circuit therefore

therefore In general for n series of resistor, Rt

Example 1 One man decides to connect two lamps of 60W@220V 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.

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

Example 3 Calculate the circuit’s current

Voltage divider

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

Parallel circuit but then

then In general

Current divider But and Therefore

Example 5 Calculate I1,I2 and I3

Example 6 Calculate the effective resistance and the power supply Hence

Example 7 Calculate the current in the 2 W resistor, given that R1 =2 W R1 =4 W I1 = I - I2 = 8 - 4 = 4A I1 and I2 are equal I1 and I2 are not equal

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

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

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

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

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

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

With many sources of e.m.f

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

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

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