Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

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

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

  1. $0.5$
  2. $0.9$
  3. $0.7$
  4. $1.1$
Reveal answer Fill a bubble to check yourself
A Correct answer
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 $A$

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

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.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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.

  1. 25 A

  2. 45 A

  3. 8A

  4. 22 A
Reveal answer Fill a bubble to check yourself
C Correct answer
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 $8A.$

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

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

  1. Microwave oven

  2. TV

  3. Radar

  4. Radio-astronomy
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

While microwave ovens use microwaves, RADAR (Radio Detection and Ranging) is a primary and critical practical application of microwave technology for navigation and detection.

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

RADAR is used for

  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
Reveal answer Fill a bubble to check yourself
D Correct answer
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

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

RADAR makes the use of.

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

RADAR systems operate by transmitting radio waves of very short wavelengths (microwaves), which reflect off objects to detect their position and speed.

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

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 $= 330\,\,m\,\,s^{-1}$)

  1. $3500 Hz$
  2. $4000 Hz$
  3. $5000 Hz$
  4. $3000 Hz$
Reveal answer Fill a bubble to check yourself
C Correct answer
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 $ 

Multiple choice 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

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

  1. heat energy only

  2. light energy only

  3. heat and light energy

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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

Multiple choice 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

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

  1. solar complex

  2. solar panel

  3. solar battery

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

Multiple choice 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

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

  1. heat energy only

  2. light energy only

  3. both heat and light energy

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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