The third day of the ICTS-SSWP 20261 was an eye-opener as we attended a session titled “Working Through Problems” by Dr. Anwesh Majumder from TIFR. At a first glance, the problems looked simple and straightforward. However, the discussions revealed that even basic ideas can hide small details that are easy to miss.

The session began with a problem from mechanics, centered on the concept of inertial frames. Initially, it looked simple and straightforward. But the discussion quickly exposed a few gaps in the understanding of the concept.

This discussion focused on application of relative motion concepts between velocity and acceleration. We can apply relative motion concepts for velocity as velocity can be relative. We know that velocity can appear different to observers in different inertial frames. Acceleration, however, is absolute. Unlike velocity, acceleration does not transform in the same way between inertial frames. This subtle difference formed the foundation of the discussion and helped clarify common misconceptions.

We then revisited the commonly confused ideas of centrifugal and centripetal forces. It was emphasized that centrifugal force is a pseudo-force that arises only when motion is analyzed from a non-inertial frame of reference. Another important clarification was that there is no separate physical force called a centripetal force. It is just the net inward force resulting from one or more real forces, which produces the required centripetal acceleration.

We also discussed several other familiar topics from a fresh perspective. These included misconceptions arising from displacement – time graphs, the actual trajectory of a boat in river-crossing problems, and the direction of acceleration of a pendulum bob at different points in its motion.

We then moved on to electrostatics, where the interpretation of electric field lines was explored. A key takeaway was that field lines do not represent the actual path followed by a charged particle. Rather, they indicate the direction of the electric force at each point in space, with the force acting tangentially to the field line. Consequently, a charged particle initially accelerates in the direction of the field at its location, while its subsequent trajectory depends on its velocity and the forces acting on it.

A simple argument helped illustrate this idea. Consider a curved electric field line. If a charged particle were to follow that curve exactly, it would require a centripetal acceleration toward the center of curvature. Such an acceleration would necessitate an additional force in that direction. Since the electric field exerts force only along the tangent to the field line, no such force exists. Therefore, the assumption that charges move along field lines cannot be correct.

A few of us also had an opportunity to speak with Dr. Majumder during lunch. We discussed a question that could not be explored in detail during the session because of time constraints. One of the most valuable insights from that conversation was a reminder that physics is ultimately about understanding the real world. While mathematical reasoning is essential, arriving at meaningful conclusions often requires physical intuition and common sense in addition to formal mathematical approaches - modeling, simulation, solving equations, etc.. Mathematics provides the framework, but intuition helps connect it to reality.

Later in the day, we had a lab session on the Fresnel and Fraunhofer diffraction. By observing the diffraction patterns formed on a screen, we learnt why diffraction is classified into these two types. The nature of the pattern depends mainly on the distance between the source and the aperture. To create the conditions needed for Fraunhofer diffraction, we used a basic principle of optics: when a point source is placed at the focal point of a convex lens, the emerging light forms a parallel beam. Since parallel rays are equivalent to light coming from an infinitely distant source, this setup allowed us to simulate a source at infinity within the confines of a lab.

Overall, Day 3 reinforced important lessons:

  • even the most familiar concepts deserve careful examination
  • the value of combining mathematical reasoning with physical intuition
  • deeper insight comes from questioning assumptions and connecting theory with observation
  • creative thinking helps use existing knowledge and tools to carry-out seemingly difficult experiments


  1. ICTS SSWP-2026: The ICTS Summer School for Women in Physics (SSWP) 2026 is a 10-day residential program designed to encourage undergraduate women to pursue careers in physics through hands-on experiments, conceptual discussions, and lectures. For more details, visit ICTS. ↩