Tag: physics

Questions Related to physics

The electrical conductivity of a semiconductor increases when radiation of the wavelength shorter than $2480nm$ is incident on it.The bandgap (in eV) for the semiconductor is

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. $0.5$

  2. $0.9$

  3. $0.7$

  4. $1.1$

Show answer
Correct Option: A
Explanation:

We know that $E=\dfrac{hc}{\lambda}$

$\Rightarrow E=\dfrac{6.6 \times 10^{-34} \times 3 \times 10^{8}}{2480 \times 10^{-9}}=0.5 ev$
Therefore the band gap for the semiconductor is $0.5ev$
So the correct option is $A$

State whether given statement is True or False
The probability of electrons to be found in the conduction band of an intrinsic semiconductor at a finite temperature decreases exponentially with increasing bandgap.

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

The probability of electrons to be found in the conduction band of an intrinsic semiconductor at a finite temperature decreases exponentially with increasing bandgap because it is more difficult for the electrons to jump to the conduction band from valence band if the band gap between them is large.

Therefore the given statement is TRUE.


A transformer has 500 turns in its primary and 1000 turns in its secondary winding.The primary voltage is 200 V and the load in the secondary is 100 ohm.Calculate the current in the primary,assuming it to be a ideal transformer.
physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. 25 A

  2. 45 A

  3. 8A

  4. 22 A

Show answer
Correct Option: C
Explanation:

In usual rotation we have -

$\Rightarrow \dfrac{V _s}{V _p}=\dfrac{N _s}{N _p}$
$\therefore V _S=V _p\times \dfrac{N _s}{N _p}$
          $=200v\times \dfrac{1000}{500}$
          $=400V$
There is load resistance of $100\Omega$ in the secondary circuit. Therefore current in the secondary 
$\Rightarrow i _s=\dfrac{V _s}{R _s}=\dfrac{400V}{100\Omega}=4A$
In an ideal transformer the output power and input power are equal that is 
$\Rightarrow V _s\times i _s=V _p\times i _p$
$\therefore i _p=i _s \times \dfrac{V _s}{V _p}=4A\times \dfrac{400V}{200V}$
                            $=4A\times 2$
                            $=8A$
Hence, the answer is $8A.$

among the following, what is the most important practical application of microwave?

physics acoustics reverberation applications of reflection of sound multiple reflection of sound and reverberation

  1. Microwave oven

  2. TV

  3. Radar

  4. Radio-astronomy

Show answer
Correct Option: C

RADAR is used for

physics acoustics reverberation applications of reflection of sound multiple reflection of sound and reverberation

  1. locating submerged submarines

  2. receiving a signals in a radio receiver

  3. locating geostationary satellites

  4. detecting and locating the position of objects such as aeroplanes

Show answer
Correct Option: D
Explanation:

Radar is an acronym fro RAdio Detection And Ranging

$\rightarrow$ It is basically a detection system that uses radio waves to determine the range, angle or velocity of objects.
$\rightarrow$ More over; used for distance measurement
$\rightarrow$ Hence; can be used for detecting and locating the position of objects like aero planes

RADAR makes the use of.

physics acoustics reverberation applications of reflection of sound multiple reflection of sound and reverberation

  1. Infra-red waves of shorter wavelengths

  2. Radio-waves of very short wavelength

  3. Radio-waves of very long wavelength

  4. Ultraviolet waves of longer wavelengths

Show answer
Correct Option: B

A rocket is moving at a speed of $220\,\,m\,\,s^{-1}$ towards a stationary target, emits a sound of frequency  $1000 Hz$. Some of the sound reaching the target gets reflected back to the rocket as echo. The frequency of the echo as detected by the rocket is
(Take velocity of sound $= 330\,\,m\,\,s^{-1}$)

physics acoustics reverberation applications of reflection of sound multiple reflection of sound and reverberation

  1. $3500 Hz$

  2. $4000 Hz$

  3. $5000 Hz$

  4. $3000 Hz$

Show answer
Correct Option: C
Explanation:

As the source (i.e rocket) is moving toward the stationary target, therefore the frequency of sound detected by the target is
$\upsilon' = \dfrac{\upsilon _0\nu}{\nu - \nu _s} = \dfrac{1000 \times 330}{330 - 220} = \dfrac{1000 \times 330}{110} = 3000 Hz$
Now the target is the source (as it is the source of echo) and the rocket's detector is the observer who intercepts the echo of frequency \acute{\upsilon}. Hence, the frequency of the echo detected by the rocket is


$\upsilon" = \dfrac{\upsilon'(\nu + \nu _O)}{\nu} = \dfrac{3000(330 + 220)}{330} = 5000 Hz $ 

The energy which directly changes into electric energy in a solar cell is :

physics energy management production of electricity from solar energy solar equipment solar power solar power plant solar energy and its applications renewable and non-renewable resources renewable and non-renewable sources of energy

  1. heat energy only

  2. light energy only

  3. heat and light energy

  4. none of these

Show answer
Correct Option: B
Explanation:

A solar cell gathers sunlight. It is the light energy which is converted into electrical energy.

The group of solar cells connected in a specific pattern to produce desired magnitude of electric current is called :

physics solar equipment production of electricity from solar energy solar power alternate sources of energy solar power plant solar energy and its applications renewable and non-renewable resources renewable and non-renewable sources of energy generation of electricity

  1. solar complex

  2. solar panel

  3. solar battery

  4. none of these

Show answer
Correct Option: B
Explanation:

Solar panel refers either to a photovoltaic module, a solar hot water panel, or to a set of solar photovoltaic (PV) modules electrically connected and mounted on a supporting structure. A PV module is a packaged, connected assembly of solar cells. Solar panels can be used as a component of a larger photovoltaic system to generate and supply electricity in commercial and residential applications.

The energy which cooks food in a box type solar cooker is :

physics solar equipment production of electricity from solar energy solar power alternate sources of energy solar power plant solar energy and its applications renewable and non-renewable resources renewable and non-renewable sources of energy generation of electricity

  1. heat energy only

  2. light energy only

  3. both heat and light energy

  4. none of these

Show answer
Correct Option: A
Explanation:

In the box type solar cooker, the heat from the sunlight is used to cook the food.