Which term describes a flexible polymer containing tiny metal particles that is normally an insulator but becomes a conductor when squeezed?

• A. Micro encapsulation
• B. Thermochromic ink
• C. Quantum-tunnelling composite (QTC)
• D. Smart fibres

Answer: (C)

Think about a flexible polymer mixed with tiny metal particles. When it’s not being pressed, the metal particles are spread out enough that electrons can’t easily jump from one particle to another, so the material acts like an insulator. If you squeeze it, the particles are pushed closer together, creating paths for electrons to move either by direct contact or by quantum tunneling through the tiny gaps. That pressure-activated path turns the material into a conductor, which is exactly what a quantum-tunnelling composite does. This behavior is useful for making pressure sensors and touch switches because the conductivity responds to how much pressure is applied.

The other options don’t fit this specific mechanism: micro-encapsulation is about tiny capsules containing substances, not about changing conductivity under squeeze; thermochromic ink changes color with temperature, not electrical conduction; smart fibres is a broad category of responsive textiles, not the precise pressure-activated conductor formed by particle tunneling in a polymer.