Question

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

Answer 1

In a ballpoint pen, there is a refill which is inside the body of the pen that contains the ink and there is a ball at the end of the pen. The ink flows around this ballpoint pen and onto the paper.

Complete step by step answer
The main principle of a ballpoint pen is surface tension. Along with surface tension, gravity and capillary action are also responsible for making a pen work however the working principle is surface tension.
The ink of a ballpoint pen spreads itself over the ball of the pen. When this ball rolls over on a piece of paper, the ink will flow to the paper due to friction between the pen and the paper.
The surface tension of the ink will decide how effectively it spreads itself over the ball. If the surface tension is too high, the ink won’t spread over the ball properly however if the surface tension is too low, the ink will get spoiled on the paper. Hence, we need the perfect amount of surface tension for the ballpoint pen to work.

Hence, the correct answer will be option B.

Note
Gravity is responsible for the ink to flow downwards in a pen so in an environment with no gravity, like space, the ballpoint pen won’t work. Bernoulli’s theorem talks about the pressure difference at different points while the viscosity is shear stress that applies between different layers of a liquid and can be thought of as the friction force in the flow of ink. None of these principles contribute to the working of a ballpoint pen.