The power of a sound from the speaker of a radio is 20 mW. By tur… - Vidyadip

MCQ

The power of a sound from the speaker of a radio is $20 mW$. By turning the knob of the volume control, the power of the sound is increased to $400 mW.$ The power increase in decibels as compared to the original power is .... $dB$

✓
$13$
B
$10$
C
$20$
D
$800$

✓

Answer

Correct option: A.

$13$

a
(a)$P \propto I$
${L_1} = 10{\log _{10}}\left( {\frac{{{I_1}}}{{{I_0}}}} \right)$ and ${L_2} = 10{\log _{10}}\left( {\frac{{{I_2}}}{{{I_0}}}} \right)$
So ${L_2} - {L_1} = 10{\log _{10}}\left( {\frac{{{I_2}}}{{{I_1}}}} \right)$
= $10{\log _{10}}\left( {\frac{{{P_2}}}{{{P_1}}}} \right)$= $10{\log _{10}}\left( {\frac{{400}}{{20}}} \right)$= $10{\log _{10}}20$
=$10\log (2 \times 10)$ = $10(0.301 + 1) = 13dB$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "M.C.Q (1 Marks)" from 14. waves and sound→14. waves and sound — all question types→Physics STD 11 Science question papers→Gujarat Board STD 11 Science question papers→Gujarat Board question paper generator→

Similar questions

$P, Q$ and $R$ are three coplanar forces acting at a point and are in equilibrium. Given $P = 1.9318 \,kg \,wt$, $\sin {\theta _1} = 0.9659$, the value of $R$ is ( in kg wt)

Four bodies of masses $2, 3, 5$ and $8\,kg$ are placed at the four corners of a square of side $2\,m$ as shown. The position of $CM$ will be

A light cylindrical vessel is kept on a horizontal surface. Area of base is A. A hole of crosssectional area $'a'$ is made just at its bottom side. The minimum coefficient of friction necessary to prevent sliding the vessel due to the impact force of the emerging liquid is $(a\,<\,<\,A)$

Figure below shows a liquid being pushed out of the tube by a piston having area of cross section $2.0\,cm ^2$. The area of cross section at the outlet is $10\,mm ^2$. If the piston is pushed at a speed of $4\,cm s ^{-1}$, the speed of outgoing fluidis $.........\,cm s ^{-1}$.

Which of the following is not the transverse wave

A standing wave exists in a string of length $150\ cm$ , which is fixed at both ends with rigid supports . The displacement amplitude of a point at a distance of $10\ cm$ from one of the ends is $5\sqrt 3\ mm$ . The nearest distance between the two points, within the same loop and havin displacment amplitude equal to $5\sqrt 3\ mm$ is $10\ cm$ . Find the maximum displacement amplitude of the particles in the string .... $mm$

A lead bullet of $10\, g$ travelling at $300\, m/s$ strikes against a block of wood and comes to rest. Assuming $50\%$ of heat is absorbed by the bullet, the increase in its temperature is ........ $^oC$

$($Specific heat of lead $= 150\,J/kg, K)$

If a particle covers half the circle of radius R with constant speed then

A particle of mass $m$ oscillates with simple harmonic motion between points ${x_1}$ and ${x_2}$, the equilibrium position being $O$. Its potential energy is plotted. It will be as given below in the graph

The excess pressure due to surface tension in a spherical liquid drop of radius r is directly proportional to