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EXAM DATES: 26 SEPT TO 30 SEPT
DFCCIL’21 EE: Daily Practices Quiz 09-Sep-2021
Each question carries 1 mark.
Negative marking: 1/4 mark
Total Questions: 06
Time: 08 min.
Q1. The ratio of the mobility to the diffusion coefficient in a semi-conductor has the unit of:
Q2. A tunnel diode is
(a) An amplifying device
(b) High resistivity p-n junction diode
(c) A very heavily doped p-n junction diode
(d) A slow switching device
Q3. A silicon PN junction is forward biased with a constant current at room temperature. When the temperature is increased by 10⁰C, the forward bias voltage across the PN junction:
(a) Increases by 25 mV
(b) Decreases by 25 mV
(c) Increases by 60 mV
(d) Decreases by 60 mV
Q4. In PMMC instruments, damping torque is provided by:
(a) Eddy currents
(b) Air friction
(c) Fluid friction
(d) Thermal effect
Q5. In 3-phase induction motor the mechanical power developed in terms of air-gap power(P_ag) is:
(a) (1-s) Pag
(b) (s-1) Pag
Q6. Determine the current through the 5Ω resistor in the figure given below utilizing Thevenin’s theorem.
Sol. Relation between diffusion constant(D) and mobility(µ): D α µ ⇒D=V_Tµ
Where; V_T= thermal voltage
Sol. A tunnel diode is a very heavily doped p-n junction diode which is used as very high-speed switching device.
Sol. dV/dT=-2.5 mV/⁰C
For 10⁰C increased temperature, voltage across PN junction will decrease by 25 mV.
Sol. In PMMC instruments, damping torque is provided by eddy currents.
Sol. For 3-phase induction motor: P_mech=(1-s) P_ag