Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

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

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?

  1. $3\times 10^9$Hz
  2. $3\times 10^6$Hz
  3. $3\times 10^8$Hz
  4. $3\times 10^7$Hz
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The speed of a wave is given by v = frequency x wavelength. Here, the distance traveled in one cycle is the wavelength (lambda = 10 m). Using v = 3 x 10^8 m/s, we get frequency = v / lambda = (3 x 10^8) / 10 = 3 x 10^7 Hz.

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

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

  1. $3 > 2 > 1$
  2. $3 > 1 > 2$
  3. $1 > 2 > 3$
  4. $2 > 3 > 1$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Electromagnetic radiation frequency increases in the order: Microwave < Infrared < Ultraviolet. Therefore, Ultraviolet (3) > Infrared (1) > Microwave (2).

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

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:

  1. $10\ KV$
  2. $20\ KV$
  3. $30\ KV$
  4. $40\ KV$
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

Radio isotope useful in treating blood cancer is

  1. Cobalt 40

  2. Carbon 60

  3. Cobalt 60

  4. Carbon 14
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

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

  1. X-rays

  2. Ultraviolet rays

  3. Microwaves
  4. $\gamma$-rays
Reveal answer Fill a bubble to check yourself
C Correct answer
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.
Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

In the transformer phase difference between input and output is

  1. $0$
  2. $\dfrac {\pi}{2}$
  3. $\dfrac {\pi}{6}$
  4. $\pi$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In an ideal transformer, the primary and secondary voltages are in phase if the secondary is open-circuited, but they are in anti-phase (180 degrees or pi radians) due to Lenz's law when considering the induced EMF relative to the primary input.

Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

Transformer are used

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