A pendulum has a period of 2.0 sec. How long will it take for ten cycles? a) 10

Question

A pendulum has a period of 2.0 sec. How long will it take for ten cycles? a) 10 s (b) 20 s c) 0.2 s Two identical aircraft engines are running. The total sound measured is 100 dB. If one of the engines were turned off, the sound level would now be: a) 103 dB b) 97 dB c) 50 dB The difference between dB and dB (A) is: a) dB counts all frequencies equally and dB (A) does not b) dB are measured faster than dB (A) c) dB counts all frequencies while dB (A) only counts ultrasonic frequencies The frequency of microwaves is lower than the frequency of UV light. Which of the following is true? a) microwaves and UV light have the same wavelength b) microwaves have a shorter wavelength than UV light c) microwaves have a longer wavelength than UV light If there is an electric current, this always means: a) there is moving electric charge b) there is a potential difference less than the resistance c) the electrons have evaporated

Explanation / Answer

One cycle takes time equal to one period.

Period is T = 2s;

So, time taken for 10 cycles is t = 10T = 10X2s

or, t = 20s

So correct option is b)

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Let intensity of sound produced by one engine be I, then total intensity by the two engines is 2I;

So initial sound level is;

1 = 10log10(2I/I0), where I0 = 10-12W/m2

or, 100 dB = 10log10(2) + 10log10(I/I0)

When one engine is turned off, the intensity is I; so the new sound level is,

2 = 10log10(I/I0) = 100 dB - 10log10(2)

or, 2 = 97 dB is the new sound level.

So correct option is b)

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in dB(A) system, the magnitude of decibels at low frequencies are reduced while this does not happen in dB system.

So option a) is correct.

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frequency and wavelength are inversely proportional to each other. So lower frequency of microwave means longer wavelength for it.

So option c) is correct.

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only moving charges constitute elecric current...

So option a) is correct;

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This concludes the answers. Check the answer and let me know if it's correct. If you need any more clarification or correction, feel free to ask.....

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