3 Multiple Choice - Circuits/Waves

[planauts]

Hi, I have three M.C. questions. The answers to these questions are A, D, C.

I am not exactly sure why exactly those are the correct answer (I guessed for the first one and happened to be right).

Homework Statement

[URL]http://ploader.net/files/1ddefae5044a52afb36b512bc019aaf5.PNG[/URL]
Source: IB Examination May 2000 P1 Timezone 1

Homework Equations

The Attempt at a Solution

18. I guessed because it had the largest difference between the two frequencies. But I don't know if that is the correct explanation.

22. Clearly, my answer is in reverse order to the correct answer. I thought greater resistance means temperature is higher. Series has the greatest Resistance, which means that it should be used for high power. But clearly, that is not the correct answer.

23. I guessed D. I had trouble calculating what the question meant by open and closed. The wording in the question seemed awkward and I got it wrong because of that. If someone could guide me, it would be really nice. (I think you are supposed to use P=VI=V^2/R = RI^2.

Thanks for your help!

 

[zush]

18. That is the correct explanation
22. P=IV=V^2/R. Because of this, assuming that the voltage is constant, the greater the resistance, the less power output.
23. The top bulb would be unchanged, because the same amount of current leaves it. Its hard to explain For bulb 2, but it has to do with the fact that in parallel the more resistors are added, the smaller the equivalent resistance

 

[ehild]

23. The top bulb would be unchanged, because the same amount of current leaves it. Its hard to explain For bulb 2, but it has to do with the fact that in parallel the more resistors are added, the smaller the equivalent resistance

Think it over. Does the same current flow through the top bulb with closed/open switch? Is the equivalent resistance unchanged?

ehild