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hello~ i'm an industrial engineering student and we have a subject of basic electronics, it is a laboratory subject and i just have some questions, which I'm confused how to answer. please show me the solutions so i can also teach it to my other classmates as well, thank you in advance~

1)what changes occur in the total resistance of a circuit as additional resistances are added; (a)in series, (b)in parallel

2)why are lamps in a house lighting circuit not connected in series?

3)a small lamp is designed to draw 300mA in a 6V circuit. what is the resistance of the lamp filament?

4)a battery with an internal resistance of 1.5ohms is connected in series with resistors R1=3ohms and R2=3.5ohms, if the potential difference accross the 3ohms resistor is 9V. what is the emf of the battery?

5)determine the ideal voltage source needed by three resistors connected in series R1=6ohms R2=8ohms R3=10ohms if a required current of 0.5A flows in the circuit

6)determine the total resistane of the circuit below (image attached)

I will help you understand the principles, but we don't 'do homework' for you.  ok?

1.  You must understand ohms law for current, voltage and resistance in simple resistive, dc circuits.  Ohms law always works.  In a simple one resistor example if another resistor is placed in parallel the equivalent resistance becomes less because there are now two current paths.  If a resistor is placed in series with another resistor the total resistance becomes greater because the add together and the current is now less if the applied votage were to remain the same.

2.  Lamps are in parallel because they are the same voltage rating and are easily added when another lamp is needed.  If they were in series the voltage would be divided amongst the lamps and if they are different wattage ratings the voltage and currents are not distributable for meeting the needs of each lamps power rating.

3. This is a most simple ohms law solution.  Resistance = voltage/current.

4. This is another simple ohms law solution.  You know the total resistance of the circuit and you can calculate the current because you know the voltage across the one resistance. etc.  easy solution.

5.  Another straight forward application of ohms law.  By knowing the voltages and currents accordingly you can solve the circuit easily.

6.  This is a practice in series and parallel resistance calculations. In series they add in parallel they are product over the sum [R1xR2/(R1 + R2)].  Start at the right hand side of the network.  The 10 abd the 40 are in parallel which is then in series with the 4 which is now in parallel with the (4.5 + 1.5), etc. and work your way through the rest of the circuit.

And away you go. Have fun.  


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Electronics questions about AC, DC and digital theory.


Graduate electrical engineer with over 40 years in electronic design, manufacturing, project organization and patent review. Experience in fields of industrial and consumer electronics (audio, video, acoustics, etc.)

IEEE (Institute of Electrical and Electronics Engineers); Senior Life member AES (Audio Engineering Society), Fellow Life member

BSEE University of North Dakota

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