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A 60 W bulb and a 100 W bulb are connected in series. Which of them will glow more brightly when a constant pd is applied across the circuit. Give reason with relevant equations.
What is the case if they are connected in parallel ?

This is an ohms law question. Do you know ohms law?  Voltage is equal to current times the resistance value.  And, power is equal to voltage times the resistance.  

In the case of the 60w bulb you determine the current by P/V used in your system.

And so on for the 100w bulb.  Then working down through the solutions you can calculate the resistance of each bulb.

Next is to just consider the current through the series connected bulbs is easily calculated by  V/(R + R); then each bulb voltage is known and each power can be calculated.

And so on. If I lost you along the way, come back with a question.  The solution is knowing basic ohms law and power calculations.  

Another non-technical way of looking at it is by knowing that the 60w bulb will have a higher resistance than the 100w bulb. Therefore the voltage drop across the bulb with the higher resistance therefore the current, being the same when they are in series will result in a greater voltage drop across the higher resistance or the 60w bulb.  

You can go from there.

Hope you get the problem solved in time for the quizz from your professor.  


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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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