ELEX Pre-Board Exam 17

What is the ratio of the input impedance with series feedback to that without feedback?

• 1 + BA
• BA
• B
• 1

Which of the following is required to start oscillation?

• BA > 1
• The phase shift around the feedback network must be 180 degrees

• Both BA > 1 and the phase shift around the feedback network must be 180 degrees

• None of these

Only the condition BA = _____ must be satisfied for self-sustained oscillations to result.

• 0
• -1
• 1
• None of these

In the Wien bridge oscillator, which of the following is (are) frequency-determining components?

• Both resistors
• Both capacitors
• Both resistors and capacitors
• None of these

In which of the following applications is a pulsating dc voltage suitable?

• Battery charger
• Radio
• Stereo system
• Computer

Across which of the following components of a power supply does the average (dc) voltage exist?

• Diodes
• Secondary of transformer
• Capacitor filter
• None of these

What is the purpose of an additional RC filter section in a power supply circuit?

• Increase the dc voltage component
• Increase the ac voltage component
• Decrease the ac voltage component
• None of these

_______________ allows simplifying a one-port circuit to a current source in parallel with an impedance.

• Norton’s Theorem
• Thevenin’s Therorem
• Kirchoff’s Current Law
• Faraday’s Law of Magnetic Induction

Charge carriers move in semiconductors via two mechanisms: _____ and _______.

• drift and diffusion
• drift and avalanche
• avalanche and diffusion
• none of these

The ___________ is the minimum energy required to dislodge an electron from its covalent bond.

• barrier potential
• bandgap energy
• potential energy
• diffusion energy