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PYQ · JEE Mains 2025
In the experiment for measurement of viscosity ' $\eta$ ' of given liquid with a ball having radius $R$, consider following statements.
A. Graph between terminal velocity V and R will be a parabola.
B. The terminal velocities of different diameter balls are constant for a given liquid.
C. Measurement of terminal velocity is dependent on the temperature.
D. This experiment can be utilized to assess the density of a given liquid.
E. If balls are dropped with some initial speed, the value of $\eta$ will change.
Choose the correct answer from the options given below:
-
A
C, D and E Only
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B
A, B and E Only
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C
A, C and D Only
Correct answer
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D
B, D and E Only
Solution
<p>We know, terminal velocity of a sphere of radius R in a liquid of viscosity $\eta$,</p>
<p>$v = {2 \over 9}{{{R^2}} \over \eta }(\sigma - \rho )$ .... (1)</p>
<p>where, $\sigma$ = mass of density of sphere</p>
<p>$\rho$ = density of liquid</p>
<p>we can see, $v \propto {R^2}$ (for constant $\eta,\sigma$ & $\rho$)</p>
<p>Hence, graph between v and R is parabola.</p>
<p>As v depends on R so the terminal velocities of different diameter balls will be different.</p><p>We know, the viscosity of a liquid usually decreases as the temperature increases and $v \propto {1 \over \eta }$</p>
<p>So terminal velocity depends on the temperature. $T \uparrow \Rightarrow \eta \downarrow \Rightarrow v \uparrow$</p>
<p>As the equation $v = {2 \over 9}{{{R^2}} \over v}(\sigma - \rho )$ involves density of liquid $\rho$. So the experiment can be utilized to asses it.</p>
<p>From (1), $\eta = {2 \over 9}{{{R^2}} \over v}(\sigma - \rho )$</p>
<p>Here, $\eta$ does not depend on initial speed of the sphere. Hence, option 3 is correct.</p>
About this question
Subject: Physics · Chapter: Properties of Solids and Liquids · Topic: Elasticity
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