Emitter current in a bipolar transistor equals which of the following?

Emitter current in a bipolar transistor equals which of the following?

• A. Emitter current equals base current plus collector current
• B. Emitter current equals base current minus collector current
• C. Emitter current equals collector current
• D. Emitter current is independent of base and collector currents

Answer: (A)

In a bipolar transistor, currents at the emitter obey conservation of charge: all current entering the emitter must split into the base and the collector. The emitter current is the total current entering the emitter, and it consists of the base current plus the collector current. So Ie = Ib + Ic. The other possibilities contradict this current-balance idea: you don’t get a difference, a single collector current, or an independent emitter current. The split of emitter current into the two paths (base and collector) is what makes Ie equal Ib plus Ic.

In a bipolar transistor, currents at the emitter obey conservation of charge: all current entering the emitter must split into the base and the collector. The emitter current is the total current entering the emitter, and it consists of the base current plus the collector current. So Ie = Ib + Ic.

The other possibilities contradict this current-balance idea: you don’t get a difference, a single collector current, or an independent emitter current. The split of emitter current into the two paths (base and collector) is what makes Ie equal Ib plus Ic.