Master exam question

[eric stromberg]

The only way this problem works is if everything is in series. If there is 10 volts across the 5 ohm resistor, there are 2 amps flowing in the circuit. If the 25 ohm lamp and the 5 ohm lamp are in series, this is 30 ohms. 2 amps x 30 ohms is 60 volts across the lamps. 60 + 10 = 70.
A totally unrealistic circuit. If the lamps were in parallel, like they should be, the lamps together would be 4.17 ohms. 2 amps through this is 8.34 volts and the source would be 18.34.

 

[Eddie702]

70 volts if the three items are in series.

 

[TwoBlocked]

The only way this problem works is if everything is in series. If there is 10 volts across the 5 ohm resistor, there are 2 amps flowing in the circuit. If the 25 ohm lamp and the 5 ohm lamp are in series, this is 30 ohms. 2 amps x 30 ohms is 60 volts across the lamps. 60 + 10 = 70.
A totally unrealistic circuit. If the lamps were in parallel, like they should be, the lamps together would be 4.17 ohms. 2 amps through this is 8.34 volts and the source would be 18.34.

No they wouldn't, and that's why the question is BS. A lamp does not have a linear voltage to amps relationship. Ohms law doesn't work.

 

[infinity]

As I said, to answer a theoretical question, we have to use the info given and apply all-other-things (i.e., variables)-being-equal, or else the question cannot be answered.

Exactly, no need to complicate it. We all know what the person who wrote the question was thinking. It may have been better if they just used resistors in the question but it is what it is.