MCQs on BJT Amplification Concepts and BJT Modeling

What region must a BJT operate in to function as a linear amplifier?

• Cut-off

• Saturation

• Active

• Breakdown

What is the purpose of the AC load line in an amplifier circuit?

• To find the power dissipation

• To analyze DC behavior

• To determine the Q-point

• To evaluate signal swing limits

What is transconductance (gm) in a BJT defined as?

• IC / VCE

• Change in output voltage / input voltage

• Change in output current / change in input voltage

• IB / VBE

The unit of transconductance gm is:

• Ohm

• Siemens

• Ampere

• Volt

Which of the following expressions represents gm in terms of collector current IC and thermal voltage VT?

• gm = VT / IC

• gm = IC / VT

• gm = IC * VT

• gm = VT * IC^2

The input resistance looking into the base of a BJT is given by:

• 1 / gm

• β / gm

• VT / IC

• IC / β

What is the relationship between rπ and re?

• rπ = β * re

• rπ = re / β

• rπ = α * re

• rπ = gm * re

What is the significance of the Early effect in the hybrid-π model?

• It increases input resistance

• It makes gm non-linear

• It introduces output resistance ro

• It reduces voltage gain

In the hybrid-π model, the collector current is expressed as:

• ic = β ib

• ic = gm vbe

• ic = VCE / RC

• Both A and B

What is the formula for input resistance at the emitter re?

• re = 1 / gm

• re = β / gm

• re = VT / IB

• re = VT / IE