Tag: physics

Questions Related to physics

Temperature can be expressed as a derived quantity in terms of :

physics dynamics - explaining motion system of unit summary of si units system of units

  1. length and mass

  2. mass and time

  3. length, mass and time

  4. none of these

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Correct Option: D
Explanation:

Temperature cannot be expressed in the terms of mass, length and time. Temperature is expressed in kelvin.

The physical quantity having the same unit in all the systems of unit is :

physics dynamics - explaining motion system of unit summary of si units system of units

  1. length

  2. mass

  3. time

  4. foot

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Correct Option: C
Explanation:

Time has same unit, second, in the SI, FPS, CGS and  MKS system. Rest of the quantities have different units in  SI, FPS, CGS and MKS system.

A ______ is the interval from one noon to the next noon.

physics dynamics - explaining motion system of unit summary of si units system of units

  1. mean solar day

  2. solar day

  3. lunar day

  4. day

Show answer
Correct Option: B
Explanation:

A solar day is the interval from one noon to the next noon.

SI unit of Magnetic flux is weber and its CGS unit is maxwell. Then 1 Wb = :

physics dynamics - explaining motion system of unit summary of si units system of units

  1. $10^6$ maxwell

  2. $10^7$ maxwell

  3. $10^8$ maxwell

  4. $10^9$ maxwell

Show answer
Correct Option: C
Explanation:

Magnetic flux is the product of magnetic field and area.

As SI unit of magnetic flux is weber, so $1 \, Wb=Tesla (T)\times m^2$
where $1 \, T=10^{4} \, gauss$ and $1 m^2=10^4 cm^2$
(T and gauss is the SI and CGS unit of magnetic field )
So, $1 \, Wb=10^4 \, gauss \times 10^4cm^2=10^8 $ maxwell

$S = A(1 - e^{-Bxt})$, where S is speed and x is displacement. The unit of B is :

physics dynamics - explaining motion system of unit summary of si units system of units

  1. $m^{-1}s^{-1}$

  2. $m^{-2}s$

  3. $s^{-2}$

  4. $s^{-1}$

Show answer
Correct Option: A
Explanation:

It is given that $x$ is displacement and $t$ is time.
Unit of $x$ is $m$ and that of time t is $s$.
Since, the quantity $Bxt$ must be dimensionless.
$\implies$ Unit of B must be $m^{-1}s^{-1}$.

A zener regulated power supply consists of a $9 V $ battery connected in series with a and a zener diode. The zener diode maintains a constant voltage drop of $4V $ The current drawn by the load resistance will be :

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. $0.025 A$

  2. $0.050 A$

  3. $0.01 A$

  4. $0.015 A$

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Correct Option: A

Zener breakdown takes place if:

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. Doped impurity is low

  2. Doped impurity is high

  3. Less impurity in N-part

  4. Less impurity in P-type

Show answer
Correct Option: B
Explanation:

 Zener breakdown occurs due to heavily doped diodes.In this process electrons crosses the barrier from 

the valence band of the p-type  to the conduction band of the lightly filled n-type material.

If, a Zener diode ($V _z = 5V$ and $I _z = 10 mA$) is connected in series with a resistance and 20 V is applied across the combination, then the maximum resistance one can use without spoiling zener action is

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. 20 $k\Omega$

  2. 15 $k\Omega$

  3. 10 $k\Omega$

  4. 1.5 $k\Omega$

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Correct Option: C

The main cause of Zener breakdown is

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. the base semiconductor being germanium.

  2. production of electron-hole pairs due to thermal excitation.

  3. low doping.

  4. high doping.

Show answer
Correct Option: D
Explanation:

Zener breakdown occurs in heavily doped p-n junctions. The heavy doping makes the depletion layer extremely thin. So that, carriers cannot accelerate enough to cause ionization. Thus, current will increase in reverse bias only due to reverse breakdown voltage.

The main cause of avalanche breakdown is

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. collision by ionisation.

  2. high doping.

  3. recombination of electrons and holes.

  4. low doping.

Show answer
Correct Option: A
Explanation:

Avalanche breakdown is caused by impact ionization of electron-hole pairs. A very little current flows under reverse bias conditions and depletion region increases. The electric field in the depletion region of a diode can be very high. Electron/holes that enter the depletion region undergo a tremendous acceleration. As these accelerated carriers collide with the atoms, they can knock electrons from their bonds, creating additional electron/hole pairs and thus additional current. As these secondary carriers are swept into the depletion region, they too are accelerated and the process repeats itself.