# Electronic Devices and Circuits Questions and Answers – The Point Contact Diode

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “The Point Contact Diode”.

1. The materials that are used in the construction of point contact diode are _________
a) Silicon
b) SnTe or Bi2Te3
c) GaS or CdS
d) HgI

Explanation: The diode base of SnTe or Bi2Te3 is highly detection sensitive. They are mechanically stable over long periods of use either as harmonic generators or mixers. They are emphasized in the 2-200THz region.

2. Which of the following are true?
1) point contact diode has a metal whisker to make pressure contact during its operation
2) it has high voltage rating
3) its V-I characteristics are constant
4) it has low breakdown voltage
a) 1 and 2
b) 3 only
c) 1 and 4
d) 2 only

Explanation: The diode contains a die of a semiconductor material on which an epitaxial layer is deposited. It uses the metal whisker to make pressure contact against that layer. It has a low breakdown voltage.

3. In the forward bias condition, the resistance of point contact diode is_________
a) less than that of a general PN diode
b) greater than that of a general PN diode
c) equal to that of a general PN diode
d) varies exponentially than that of a general PN diode

Explanation: The current flow of the point contact diode is not independent of voltage applied to the crystal unlikely to a general PN diode. This characteristic of contact diode makes its capacitance high at high frequency. A small capacitive current flows in the circuit.

4. The barrier layer capacitance of a point contact diode is_________
a) 0.1pF to 1pF
b) 5pF to 50pF
c) 0.2pF to 2pF
d) 0.008µF to 20µF

Explanation: The barrier capacitance at the point is very low about 0.1pF to 1pF. The capacitance between the cat whisker and crystal is less compared to junction diode capacitance between both sides of the diode. For a general PN diode is 0.008µF to 20µF.

5. The cat whisker wire present in the contact diode is used for_________
a) for heat dissipation
b) for charge transfer between sections
c) maintaining the pressure between sections
d) preventing current flow

Explanation: The operation of a contact diode depends on the pressure of contact between semiconductor crystal and point. The cat whisker wire presses against the crystal to form a section and the section allows the current flow. This is similar to the behaviour of PN diode.
Sanfoundry Certification Contest of the Month is Live. 100+ Subjects. Participate Now!

6. The semiconductor junctions those are present in a contact diode_________
a) beryllium-copper and bronze-phosphor
b) beryllium-phosphor and bronze-copper
c) mercury-iodine
d) tin-tungsten

Explanation: The diode contains two sections having a small rectangular crystal of N type silicon and a fine beryllium-copper and bronze-phosphor. It has a tungsten wire which is called as a cat whisker wire. This helps in pressing one section to other.

7. The application of a contact diode is_________
a) Clampers and clippers
b) Voltage multipliers
c) Rectifiers
d) AM detectors

Explanation: The point contact diodes are the oldest microwave semiconductor devices. They were developed during world war 2. They have excessive applications in microwave fields and used as receivers and detectors.

8. The operating frequencies of the point contact diode is_________
a) 30KHz or above
b) 10GHz or above
c) 30GHz or above
d) 10KHz or above

Explanation: It’s used in high frequency conversions and circuits in the order of 10KHz or above. The reactance due to capacitance is high and at high frequency a very small capacitive current flows.

9. During the manufacture of point contact diode, why is a relatively large current passed from cat whisker to silicon crystal?
a) to control the amount of current flow
b) to form small region of p type material
c) to allow mechanical support for the sections
d) to form anode and cathode regions

Explanation: The behaviour of a contact diode is similar to that of a PN diode. It has a tungsten wire which is called as a cat whisker wire. This helps in pressing one section to other.

10. What is the capacitive reactance across the point contact diode when compared to normal PN junction diode?
a) lower
b) higher
c) equal
d) cannot be determined

Explanation: The current flow of the point contact diode is not independent of voltage applied to the crystal unlikely to a general PN diode. A small capacitive current flows in the circuit.

Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.

To practice all areas of Electronic Devices and Circuits, here is complete set of 1000+ Multiple Choice Questions and Answers.