Semiconductors
- The electron concentration in an n-type semiconductor is the same as hole concentration in a p-type semiconductor. An external field (electric) is applied across each of them. Compare the currents in them. Answer: 3. current in n-type > current in p-type. Key idea: I∝ n μ E , and the same concentration means the current depends on mobility. In... 1
- For transistor action, which of the following statements is correct ? Answer: 4. The base region must be very thin and lightly doped. For transistor action the base must be very thin and lightly doped, so most... 1
- For a p-type semiconductor, which of the following statements is true ? Answer: 2. Holes are the majority carriers and trivalent atoms are the dopants. A p-type semiconductor is made by doping silicon or germaniu... 1
- In the circuit shown in the figure, the input voltage V_i is 20 V, V_BE = 0 and V_CE = 0. The values of I_B, I_C and β are given by Answer: 4. I_B = 40 μ A, I_C = 5 mA, β = 125 From the figure: R_B=500\ kΩ , R_C=4\ kΩ , supply 20 V, V_i=20 V, with V_BE=0 and V_CE=0 . I_B=... 1
- In a common emitter transistor amplifier the audio signal voltage across the collector is 3 V. The resistance of collector is 3 kΩ. If current gain is 100 and the base resistance is 2 kΩ, the voltage and power gain of the amplifier is : Answer: 2. 150 and 15000 Key idea: in a common emitter amplifier, voltage gain A_v=βR_C/R_B and power gain =β A_v . A_v=100×3\ kΩ/2\ kΩ=150... 1
- For CE transistor amplifier, the audio signal voltage across the collector resistance of 2 kΩ is 4 V. If the current amplification factor of the transistor is 100 and the base resistance is 1 kΩ, then the input signal voltage is Answer: 1. 20 mV In a CE amplifier, V_out=I_CR_C and I_C=β I_B ; input voltage is V_in=I_BR_B . I_C=4/2000=2 mA. I_B=I_C/β=2\ mA/100=20\ μA... 1
- A npn transistor is connected in common emitter configuration in a given amplifier. A load resistance of 800 Ω is connected in the collector circuit and the voltage drop across it is 0.8 V. If the current amplification factor is 0.96 and the input re… Answer: 1. 4, 3.84 Key idea: in common emitter, A_v=βR_L/R_i and power gain =β A_v . The question uses 0.96 as the current gain β in these f... 1