Decibels

Q. A rock band gives rise to an average sound level of $100\text{dB}$ at a distance $20\text{m}$ from the centre of the band. As an approximation, assume that the sound radiated by the band spreads out in the shape of a sphere centred at the band. What is the power of sound produced by the band?

1. $80\text{W}$
2. $50\text{W}$
3. $20\text{W}$
4. $10\text{W}$

Q. Calculate the change in intensity level when the intensity of sound increases by ${10}^6$ times its original intensity.

1. $60\text{dB}$
2. $50\text{dB}$
3. $40\text{dB}$
4. $30\text{dB}$

Q. At a distance of $10\text{m}$ from a point source, loudness is found to be $20\text{dB}$. The distance from the source where loudness is $0\text{dB}$ is

1. $20\text{m}$
2. $50\text{m}$
3. $100\text{m}$
4. $\infty$

Q. How many times does the electron of hydrogen atom go round the first Bohr orbit in one $\text{second}$?
$[m=9.1\times {10}^{-31}\text{kg},e=1.6\times {10}^{-19}\text{C}{\epsilon }_0=8.85\times {10}^{-12}{\text{F m}}^{-1},h=6.6\times {10}^{-34}\text{J s}]$

1. $6.6\times {10}^5$
2. $6.6\times {10}^{10}$
3. $6.6\times {10}^{13}$
4. $6.6\times {10}^{15}$

Q. Determine the ratio of perimeter of $2^{nd}$ and $3^{rd}$ Bohr orbit in ${\text{He}}^{+}$ atom $(Z=2)$.

1. $\frac{4}{9}$
2. $\frac{9}{4}$
3. $\frac{16}{9}$
4. $\frac{9}{16}$

Q. Determine the ratio of perimeter of $2^{nd}$ and $3^{rd}$ Bohr orbit in ${\text{He}}^{+}$ atom $(Z=2)$.

1. $\frac{9}{4}$
2. $\frac{16}{9}$
3. $\frac{4}{9}$
4. $\frac{9}{16}$