Tag: physics

Questions Related to physics

If the distance that a radio wave can travel in the time of one complete cycle is $10$ metres, then the frequency of the radio wave in cycles per second is?

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. $3\times 10^9$Hz

  2. $3\times 10^6$Hz

  3. $3\times 10^8$Hz

  4. $3\times 10^7$Hz

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Correct Option: D

Study the frequency of the following electromagnetic radiations and select the correct relationship.
$1$. Infra red
$2$. Microwave
$3$. Ultra violet.

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. $3 > 2 > 1$

  2. $3 > 1 > 2$

  3. $1 > 2 > 3$

  4. $2 > 3 > 1$

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Correct Option: B

International broadcasting requires.

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. Medium frequency radio waves

  2. High frequency radio waves

  3. Low frequency radio waves

  4. Longitudinal waves

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Correct Option: B
Explanation:

International broadcasting requires high frequency radio waves which have high energy to travel over long distance.

A beam of electrons accelerated by a large potential difference $V$ is made to strike a metal target to produce $X-$rays. For which of the following values of $V$, the resulting $X-$rays have the lowest minimum wave length:

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. $10\ KV$

  2. $20\ KV$

  3. $30\ KV$

  4. $40\ KV$

Show answer
Correct Option: D
Explanation:

As we know, $\boxed{E _{max}=\dfrac{hc}{\lambda _{min}}}$

$\boxed{\lambda _{min}=\dfrac{hc}{ev}}$
Here the value of $v$ is given as $10kv,20kv,30kv,40kv$
A, $\boxed{\lambda \propto \dfrac{1}{V}}$, large value of $V$
$\Rightarrow$ min. value of $\lambda$
Hence for $40kv$, $\lambda _{min}$ is minimum.
$\therefore$ option $D$ is correct.

Radio isotope useful in treating blood cancer is

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. Cobalt 40

  2. Carbon 60

  3. Cobalt 60

  4. Carbon 14

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Correct Option: C
Explanation:

Cobalt therapy or cobalt $60$ therapy is the medical use of gamma rays from the radio isotope cobalt $-60$ to treat conditions such as cancer. Thus, Cobalt $-60$ is the radio isotope useful in treating the blood cancer.

The operating voltage in coolidge tube is ${10}^{5}V$. The speed of X-Rays produced is ________ $m{s}^{-1}$

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. $2\times { 10 }^{ 8 }\quad $

  2. ${ 10 }^{ 6 }$

  3. ${ 10 }^{ 5 }$

  4. $3\times { 10 }^{ 8 }$

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Correct Option: D
Explanation:

X-ray is an electromagnetic waves which moves with a speed equal to   $3\times 10^8 \ m/s$

For an electromagnetic radiation,

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. only momentum is quantised

  2. only energy is quantised

  3. both energy and momentum are
    quantised

  4. neither of them is quantised

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Correct Option: A
Explanation:

For an electromagnetic radiation, only momentum is quantised$.$

Hence,
option $(A)$ is correct answer.

If a source of power $4$ kW produces $10^{26}$ photons/second, the radiation belongs to a part of the spectrum called:

physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

  1. X-rays

  2. Ultraviolet rays

  3. Microwaves

  4. $\gamma$-rays

Show answer
Correct Option: C
Explanation:
$4000 \ J$ of energy is produced from $10^{26}$ photons in one second.
Energy of each photon   $E = \dfrac{4000}{10^{26}} = 4\times 10^{-23} \ J$
Frequency of each photon   $\nu = \dfrac{E}{h} = \dfrac{4\times 10^{-23}}{6.63\times 10^{-34}} = 6\times 10^{10} \ Hz$
So the radiation belongs to micro waves.
Correct answer is option C.

In the transformer phase difference between input and output is

physics electro-magnetism applications of electromagnets transformer transformers

  1. $0$

  2. $\dfrac {\pi}{2}$

  3. $\dfrac {\pi}{6}$

  4. $\pi$

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Correct Option: D

Transformer are used

physics electro-magnetism applications of electromagnets transformer transformers

  1. in $DC$ circuits only

  2. in $AC$ circuits only

  3. in both $DC$ and $AC$ circuits

  4. neither in $DC$ nor in $AC$ circuits.

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Correct Option: B
Explanation:

Transformer is an electrical device that requires time varying current to link two or more electrical coils through electromagnetic induction and thus transfer energy between the magnetically coupled circuits. Therefore transformer are used only in AC circuits