The black box puzzle

Status
Not open for further replies.

lordsathish

Full Member level 5
Joined
Feb 11, 2006
Messages
246
Helped
33
Reputation
66
Reaction score
3
Trophy points
1,298
Location
Asia
Activity points
2,698
while surfing i found such a question...
i couldn find the answer...
could you help me...
You go to the lab, and connect a battery across the terminals of a black box. Then, using the instruments on the bench, you measure the following:
Voltage across the terminals: 1 V.
Current entering the box: 2 A.
Power dissipation of the box (measured by a watt meter): 0 W.
What is in the box?



Thank you...
 

Re: question

nothing in this box
 

Re: question

if you're in AC, could be an ideal inductor or capacitor, or a combination of both, but without resistors, since P = 0W

Best Regards
 

Re: question

The box could contain a 1 volt battery in series with a 0.5 ohm resistor. If you measure the voltage with a high impedance voltmeter, no current will flow and you will measure the battery voltage of 1 volt. If you measure the current with a zero resistance ammeter, then the current will follow Ohm's law (1 volt/0.5 ohm) and will be 2 amperes. If you measure the power dissipation of the box, it will be zero since no current wil flow if no load is connected to the box's terminals; 0 watts are dissipated.
 

Re: question

Can you tell us the power source AC or DC? If AC then the box simply has a purely inductive load. If DC then what kind of watt-meter are you using?
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…