Electronics Engineering (ELEX) Board Practice Exam

The Q of a crystal is typically ______.

1. 500

2. 1000

3. 10000

4. 20000

The correct answer is: 20000

The Q factor, or quality factor, of a crystal is a measure of its efficiency in resonance. It indicates how selective the crystal is at its resonant frequency and is a reflection of how little energy is lost per cycle of oscillation relative to the energy stored. A higher Q factor signifies lower energy loss, which results in sharper resonance peaks and better frequency stability. In the case of crystals, common values of the Q factor can range widely depending on the design and material used. Typical Q factors for high-quality crystals can indeed reach 20,000 or even higher in some specialized applications. These high Q values are due to the crystal’s ability to sustain oscillations with minimal damping, which is crucial for applications requiring precise frequency control, such as in oscillators and filters. Values lower than this, like 500 or 1000, might apply to other resonant elements or lower-quality crystals, but they do not reflect the characteristics of high-quality quartz crystals typically used in electronics. Hence, 20,000 is frequently considered a standard representation for the Q of a crystal in high-performance applications, demonstrating its efficacy and reliability in resonant circuits.