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Electronics and Communication Engineering - Electromagnetic Field Theory

Exercise : Electromagnetic Field Theory - Section 2
46.
Which statement is false as regards holes
Holes exist in conductors as well as semiconductors
Holes constitute positive charges
Holes exist only in semiconductors
Holes and electrons recombine
Answer: Option
Explanation:

Holes do not exist in conductors.

47.
Photo electric emission can occur only if
wave length of incident radiation is equal to threshold value
wave length of incident radiation is less than threshold value
frequency of incident radiation is less than threshold frequency
none of the above
Answer: Option
Explanation:

The frequency of incident radiation has to be more than threshold value. Wavelength is inversely proportional to frequency.

Therefore wavelength of incident radiation must be less than threshold value.

48.
The reverse saturation current of a diode does not depend on temperature.
True
False
Answer: Option
Explanation:

It increases with increase of temperature.

49.
In a piezoelectric crystal, application of a mechanical stress would produce
plastic deformation of the crystal
magnetic Dipoles in the crystal
electric polarization in the crystal
shift in the Fermi level
Answer: Option
Explanation:

Commonly material used as piezoelectric crystal is Barium Nitrate. Generally ferroelectric crystals and piezoelectric.

50.
The value of a in a transistor
is always equal to 1
is less than 1 but more than 0.9
is about 0.4
is about 0.1
Answer: Option
Explanation:

a is about 0.98.

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