Question

A biochemist is pelleting down the microsomal fraction from a sample using ultracentrifuge at a speed of 20000 rpm. What would be RCF if the diameter of the rotor is 7 cm?

• A. 15680
• B. 31360
• C. 7840
• D. 3920

Hint:

Always halve the diameter to find the radius before applying the RCF formula. Keep scientific notation in mind for large rpm values.

Answer 1

The Correct Option is A

Step 1: Understand the formula for RCF (Relative Centrifugal Force): \[ {RCF} = 1.118 \times 10^{-5} \times r \times ({rpm})^2 \] Where:
\( r \) is the radius in cm (half of the diameter),
\( {rpm} \) is the speed of rotation.
Step 2: Substitute the values:
Diameter = 7 cm, so radius \( r = \frac{7}{2} = 3.5 \) cm
rpm = 20000
\[ {RCF} = 1.118 \times 10^{-5} \times 3.5 \times (20000)^2 \] \[ = 1.118 \times 10^{-5} \times 3.5 \times 4 \times 10^8 \] \[ = 1.118 \times 3.5 \times 4 \times 10^3 = 15.652 \times 10^3 = 15652 \approx 15680 \] Step 3: Round off to the nearest value.
The closest value among the options is 15680.