Question

The working principle of a ballpoint pen is :
A. Bernoulli’s theorem
B. Surface tension
C. Gravity
D. Viscosity

Answer 1

Hint: The ballpoint pen has a refill and a tip where the ball is located at the end point of the tip. There is a bit gap between the tip and the ball. Now the ink will flow from the refill to the gap between the ball holder and ball. There are separate mechanisms which will make ball point pen work.

Complete step by step answer:
The main principles for the working of the ballpoint pen are surface tension and capillary action.
When we insert the tube in the vessel of water then due to capillary action even though initially the water surface would be concave and due to the domination of adhesive forces the water would go up in the capillary and the surface would become flat in order to reduce the surface area and to reduce the surface energy. The surface tension is the reason for this.
Same happens with the ball point pen. The refill is like the vessel and the ink is like the water and the ball holder is like the tube. Now due to capillary action the ink will come out of refill and enter the ball holder and the gap between that and due to the friction between the ball and the paper the ball rolls and the ink will stick on the paper after sometime. Now if surface tension is more then ink will not spread properly. If the surface tension is less then ink might get spoiled.
So the surface tension is responsible for the working of the ballpoint pen.

So, the correct answer is “Option B”.

Note: If we talk about the bernoulli’s law when the wind flows the paper on the calendar will fly up because the pressure under the page will be more and the pressure on the top will be less as the velocity of air on the top of the page is more and the velocity of air at the bottom of the page is less.