If an emitter current is changed by 4 mA, the collector current changes by 3.5 mA. The value of β will be :

Solution

Physics sir · 3 steps

Find the base current first: whatever the collector does not take from the emitter goes to the base.

1. Current split. In a transistor the emitter current divides between collector and base, so I_E = I_C + I_B. The same holds for changes: Δ I_E = Δ I_C + Δ I_B.
2. Base current change. Δ I_B = Δ I_E - Δ I_C = 4 - 3.5 = 0.5 mA.

   β = (Δ I_C)/(Δ I_B) = (3.5 mA)/(0.5 mA) = 7

3. So. The current gain is β = 7, which is option (d).

The idea to keep. α compares collector current with emitter current, and β compares collector current with base current. If you are given I_E and I_C, get I_B = I_E - I_C first, or use β = α/(1-α).

Answer from the NTA final answer key. Solution by PrepWiser.