Indicate which one of the following system is digital
|
(a) Pulse position modulation |
(b) Pulse code modulation |
|
(c) Pulse width modulation |
(d) Pulse amplitude modulation |
(b) Pulse code modulation
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There is a current of 20 amperes in a copper wire of 
square metre area of cross-section. If the number of free electrons per cubic metre is 
, then the drift velocity is
|
(a) 125 |
(b) 12.5 |
(c) 1.25 |
(d) 1.25 |
A parallel plate capacitor is charged and the charging battery is then disconnected. If the plates of the capacitor are moved further apart by means of insulating handles, then
|
(a) The charge on the capacitor increases |
|
(b) The voltage across the plates decreases |
|
(c) The capacitance increases |
|
(d) The electrostatic energy stored in the capacitor increases |
For photoelectric emission, tungsten requires light of 2300 Å. If light of 1800 Å wavelength is incident then emission
|
(a) Takes place |
(b) Don’t take place |
|
(c) May or may not take place |
(d) Depends on frequency |
Which is the correct relation for forbidden energy gap in conductor, semi conductor and insulator
|
(a) |
|
(b) |
|
(c) |
|
(d) |
A battery is connected between two points A and B on the circumference of a uniform conducting ring of radius r and resistance R. One of the arcs AB of the ring subtends an angle θ at the centre. The value of the magnetic induction at the centre due to the current in the ring is
|
(a) Proportional to 2(180° - θ) |
(b) Inversely proportional to r |
|
(c) Zero, only if θ = 180° |
(d) Zero for all values of θ |
Between the plates of a parallel plate condenser there is 1mm thick paper of dielectric constant 4. It is charged at 100 volt. The electric field in volt/metre between the plates of the capacitor is
|
(a) 100 |
(b) 100000 |
(c) 25000 |
(d) 4000000 |
