91Ó°ÊÓ

The speed of the centrifuge varies with the variation in the distance between the particle and centre of rotation, acceleration of the particle. With the help of speed, the rotation of the centrifuge can be evaluated.

The given data can be listed below as,

• The distance of a particle from the centre of the rotation is, $r=7\mathrm{cm}\left(\frac{1\mathrm{m}}{100\mathrm{cm}}\right)=0.07\mathrm{m}$.
• The acceleration of particle is, $a_c=125000g\text{'}\mathrm{s}$.

The speed of the particle can be expressed as,

$v=\sqrt{a_{\mathrm{c}}r}$

Here, $a_c$is the centripetal acceleration of the particle.

Substitute the values in the above equation.

$\begin{array}{c}v=\sqrt{125000g\left(\frac{9.81\mathrm{m}/{\mathrm{s}}^2}{1g}\right)×0.07\mathrm{m}}\\ v=\sqrt{85837.5}\mathrm{m}/\mathrm{s}\\ v=292.98\mathrm{m}/\mathrm{s}\end{array}$

The speed of the particle can be expressed as,

$\begin{array}{c}v=\frac{2\mathrm{Ï€}r}{T}\\ v=\left(\frac{2\mathrm{Ï€}r}{\frac{1}{N}}\right)\\ \frac{1}{N}=\left(\frac{2\mathrm{Ï€}r}{v}\right)\\ N=\left(\frac{v}{2\mathrm{Ï€}r}\right)\end{array}$

Here, N is the rotation of the centrifuge, T is the time taken by the particle.

Substitute the values in the above equation.

$\begin{array}{c}N=\frac{292.98\mathrm{m}/\mathrm{s}\left(\frac{60\mathrm{s}}{1\min }\right)}{2\mathrm{π}×0.07\mathrm{m}}\\ =3.99×{10}^4\mathrm{rpm}\end{array}$

Thus, the rotation of a centrifuge is $3.99×{10}^4\mathrm{rpm}$.