Crystal transducers and the piezoelectric phenomenon A crystal generates a small voltage when mechanical stress is applied across it. This behavior is known as which effect?

Introduction / Context:
Piezocrystals such as quartz convert mechanical stress to electrical charge and vice versa. This bidirectional electromechanical coupling is the basis of timing resonators, ultrasonic transducers, and vibration sensors. The direct effect produces a voltage from applied stress; the converse effect produces strain when an electric field is applied.

Given Data / Assumptions:

• Material is a suitable crystalline piezoelectric (for example, quartz, PZT ceramics).
• Mechanical force or stress is applied across the crystal.
• Result observed is a small generated voltage or charge.

Concept / Approach:
The direct piezoelectric effect: charge generation Q is proportional to applied force F with proportionality d (piezoelectric coefficient). In sensing, electrodes collect this charge, which appears as a voltage across a load or preamplifier input. The effect is linear within a small-signal range and highly repeatable in stable crystals, enabling precise oscillators when combined with feedback networks.

Step-by-Step Solution:

Verification / Alternative check:
Quartz crystals in oscillators rely on the converse effect to vibrate when driven; the same crystal used as a pickup can generate a measurable voltage under mechanical excitation, confirming the direct effect.

Why Other Options Are Wrong:

• Photoelectric: requires photons ejecting electrons from a surface, not mechanical stress.
• Co-pitts: not a standard physical effect; likely a distractor.
• Flywheel: refers to rotational inertia, unrelated to electromechanical coupling.

Common Pitfalls:
Confusing piezoelectric with pyroelectric (temperature-induced charge) or magnetostrictive (magnetic-field-induced strain).

Final Answer:
piezoelectric