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- Question
Which of the following is used in automatic control of street lights?
Options- A. Thermistor
- B. Photoconductor
- C. Transistor
- D. Varistor
- Correct Answer
- Photoconductor
- 1. Assertion (A): Doping level in extrinsic semiconductors is very small.
Reason (R): Additional of impurity in the ratio of 1 part in 108 parts increases the number of charge carriers by about 20.
Options- A. Both A and R are true and R is correct explanation of A
- B. Both A and R are true but R is not correct explanation of A
- C. A is true but R is false
- D. A is false but R is true Discuss
- 2. When a dielectric is subjected to an electric field E, each volume element of dielectric can be considered to be carrying an electric dipole moment.
Options- A. True
- B. False Discuss
- 3. Which of these has the highest dielectric strength?
Options- A. Mica
- B. Air
- C. Cotton
- D. Rubber Discuss
- 4. The temperature coefficient of resistivity of semiconductors is
Options- A. positive
- B. negative
- C. may be positive or negative
- D. very low Discuss
- 5. A good dielectric should have
Options- A. low losses
- B. good heat conductivity
- C. high intrinsic strength
- D. all of the above Discuss
- 6. A leaky dielectric has ?r = ?r' - j?r". If a field E is applied, the current component in phase with E is proportional to ?r".
Options- A. True
- B. False Discuss
- 7. The colour code on a carbon resistor is yellow-violet-orange. The value of resistance is
Options- A. 17000 ?
- B. 27000 ?
- C. 37000 ?
- D. 47000 ? Discuss
- 8. An electron in a metal suffers collision and if the probability of it being scattered over an angle d? is 2p P(?) sin ? d? where P(?) is an arbitrary function of scattering angle ?, then
Options- A.
2pP(?) sin ? d? = 0 - B. 2pP(?) sin ? d? = 2
- C. 2pP(?) sin ? d? = -1
- D. 2pP(?) sin ? d? = 1
Discuss
- 9. The relation between thermal conductivity K (W/m/°C), heat flow density Q (watt/m2) and dT/dx (°C per metre) is
Options- A. Q = K(dT/dx)
- B. Q = - K(dT/dx)
- C. K = Q(dT/dx)
- D. dT/dx = - QK Discuss
- 10. Assertion (A): Ionic solids, in general, have no electrical conductivity.
Reason (R): In ionic solids, electrons are tightly bound to the nucleus.
Options- A. Both A and R are true and R is correct explanation of A
- B. Both A and R are true but R is not correct explanation of A
- C. A is true but R is false
- D. A is false but R is true Discuss
Materials and Components problems
Search Results
Correct Answer: Both A and R are true and R is correct explanation of A
Correct Answer: True
Correct Answer: Mica
Correct Answer: negative
Explanation:
Resistance of semiconductors decreases with increase in temperature.
Correct Answer: all of the above
Correct Answer: True
Correct Answer: 47000 ?
Correct Answer:
2pP(?) sin ? d? = -1 Correct Answer: Q = - K(dT/dx)
Correct Answer: Both A and R are true and R is correct explanation of A
Explanation:
If electrons are tightly bound, conductivity is not there.
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