# Can someone figure these out?

Discussion in 'Homework Help' started by HVACIV, Jul 4, 2009.

1. ### HVACIV Thread Starter New Member

Jul 4, 2009
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As the frequency of an AC circuit is increased, a inductor looks more like a/an
A) short
C) open

Two 10 ohms resistors in parallel across a 600 Vdc source would consume a total of :
A) 3.6 kW
B) 72 KW
C) 360 W
D) 7.2 kW

If the voltage of a circuit is fixed and the temperature of the air surrounding the circuit begins to increase:
A) power consumption increases
B)current decreases

2. ### natishalom New Member

Nov 3, 2008
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hi.
the answer to the second question is 72KW.

Jul 4, 2009
1
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Hi

If frequency (f) is incresed, the inductive reactance XL = 2(pi)fL increases. Reactance which is supposed to be the ressistacne of the inductance poses more resistance to the current flowing into it. As u increase the frequnecy, its literally gets verry less current and therefore acts as an open circuit
Hope this helps !!

4. ### R!f@@ AAC Fanatic!

Apr 2, 2009
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I is D
2 is B
3 is A

Still Circumstances should be accounted for though

Rifaa

5. ### Beduin Member

May 20, 2009
16
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Hi there

Care to explane # 3, please?

Last edited: Jul 5, 2009
6. ### R!f@@ AAC Fanatic!

Apr 2, 2009
9,647
1,111
In a closed enclosure with a powered circuit dissipating heat and if there is no air flow, the ambient temperature will keep on rising to the point where passive components melt ( meaning internal resistance drops causing the increase in power dissipation ), and if a semiconductor is there, the heat will cause thermal runaway which results in increasing power dissipation.

Atleast this is what happened to my sealed circuits, if the surrounding cannot vent heat

Rifaa