An LED has a rating of 2 V and 10 mA. It is used along with 6V battery. The rang

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Question
An LED has a rating of 2 V and 10 mA. It is used along with 6V battery. The range of series resistance is
Options
A. 0 to 200 ?
B. 200 - 400 ?
C. 200 ? and above
D. 400 ? and above

Correct Answer

400 ? and above

Explanation

R =

An LED has a rating of 2 V and 10 mA. It is used along with 6V battery. The range of series resistan

= 400?.

R must be at least 400? so that current in LED does not exceed 10 mA.

Electronic Devices and Circuits problems

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1. Assertion (A): When a high reverse voltage is applied to a p-n junction the diode breaks down.
Reason (R): High reverse voltage causes Avalanche effect.
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 a correct explanation of A
C. A is true but R is false
D. A is false but R is true

2. A periodic voltage has following value for equal time intervals changing suddenly from one value to next... 0, 5, 10, 20, 50, 60, 50, 20, 10, 5, 0, -5, -10 etc. Then rms value of the waveform is
Options
A. 31 V
B. 32 V
C. insufficient data
D. none of these

3. As compared to an ordinary semiconductor diode, a Schottky diode
Options
A. has lower cut in voltage
B. has higher cut in voltage
C. lower reverse saturation current
D. both (b) and (c)

4. In a zener diode
Options
A. the forward current is very high
B. sharp breakdown occurs at a certain reverse voltage
C. the ratio v-i can be negative
D. there are two p-n junctions

5. In an n-p-n transistor biased for operation in forward active region
Options
A. emitter is positive with respect to base
B. collector is positive with respect to base
C. base is positive with respect to emitter and collector is positive with respect to base
D. none of the above

6. Work function of oxide coated cathode is much lower than that of tungsten cathode.
Options
A. True
B. False

7. Assertion (A): A p-n junction has high resistance in reverse direction.
Reason (R): When a reverse bias is applied to p-n junction, the width of depletion layer increases.
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 a correct explanation of A
C. A is true but R is false
D. A is false but R is true

8. The minority carrier life time and diffusion constant in a semiconductor material are respectively 100 microsecond and 100 cm²/sec. The diffusion length is
Options
A. 0.1 cm
B. 0.01 cm
C. 0.0141 cm
D. 1 cm

9. As compared to an ordinary semiconductor diode, a Schottky diode
Options
A. has higher reverse saturation current
B. has higher reverse saturation current and higher cut in voltage
C. has higher reverse saturation current and lower cut in voltage
D. has lower reverse saturation current and lower cut in voltage

10. In a p type material the Fermi level is 0.3 eV above valence band. The concentration of acceptor atoms is increased. The new position of Fermi level is likely to be
Options
A. 0.5 eV above valence band
B. 0.28 eV above valence band
C. 0.1 eV above valence band
D. below the valence band

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