Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

Multiple choice deflection of electron beam by magnetic field observing the force and electron beam tubes charged particles electromagnetic forces physics

The minimum amount of energy released in annihilation of electron-positron is.

  1. $1.02\ MeV$

  2. $0.58\ MeV$

  3. $185\ MeV$

  4. $200\ MeV$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Energy released during the annihilation of ${ e }^{ - },{ e }^{ + }$ pair is,
$E=2{ m } _{ c }{ C }^{ 2 }$
$E=2\times 9.1\times { 10 }^{ -31 }\times { \left( 3\times { 10 }^{ 8 } \right)  }^{ 2 }J$
$E=\dfrac { 2\times 9.1\times 9\times { 10 }^{ -15 } }{ 1.6\times { 10 }^{ -13 } } MeV$
$E=1.02MeV$
Multiple choice deflection of electron beam by magnetic field observing the force and electron beam tubes charged particles electromagnetic forces physics

A spherical drop of radius $10$ has absorbed $40$ electrons. The energy required to given an additional electron to it is.

  1. $9.2 \times 10^{-21} J$

  2. $5.7 \times 10^{-21} J$

  3. $9.21 \times 10^{-23} J$

  4. $4Ke^2$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
We know that,
Energy $=$ Potential $\times $ Charge
$E=\left( \dfrac { k\quad q }{ r }  \right) \times e$
$E=\dfrac { k\left( 40e \right) \left( e \right)  }{ 10 } $
$E=4k{ \left( e \right)  }^{ 2 }$
$\boxed { Energy=4{ ke }^{ 2 } } $
Multiple choice deflection of electron beam by magnetic field observing the force and electron beam tubes charged particles electromagnetic forces physics

Cathode rays enter an electric field normal to the field. Then their path in the electric field is :

  1. A parabola

  2. A circle

  3. A straight line

  4. An ellipse
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Electric field applies a constant force  $eE$ on the electrons (i.e. cathode rays) perpendicular to the beam of electrons due to which the electrons will trace a parabolic path.

Multiple choice deflection of electron beam by magnetic field observing the force and electron beam tubes charged particles electromagnetic forces physics

Out of the following transitions, the frequency of emitted photon will be maximum for 

  1. $n = 5$ to $n = 3$

  2. $n = 6$ to $n = 2$

  3. $n = 2$ to $n = 1$

  4. $n = 1$ to $n = 2$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The frequency of an emitted photon is proportional to the energy difference of the transition (E = hf). The energy difference is greatest for the n=2 to n=1 transition in the hydrogen atom, as the energy levels are spaced further apart at lower quantum numbers.

Multiple choice deflection of electron beam by magnetic field observing the force and electron beam tubes charged particles electromagnetic forces physics

When electron is incident on molybdenum they by changing energy of electron:-

  1. $\lambda _{\text{min}}$ changes

  2. $\lambda _{\text{min}}$ remains constant

  3. $\lambda _{K _{\alpha}}, \lambda _{K _{\beta}}$ changes

  4. $\lambda _{\text{min}}, \lambda _{K _{\alpha}}$ and $\lambda _{K _{\beta}}$ all changes
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The minimum wavelength (lambda_min) of X-rays produced is determined by the accelerating voltage (or energy) of the incident electrons via the Duane-Hunt law, lambda_min = hc/eV. Characteristic X-ray wavelengths (K_alpha, K_beta) depend on the target material (molybdenum), not the incident electron energy.

Multiple choice deflection of electron beam by magnetic field observing the force and electron beam tubes charged particles electromagnetic forces physics

An electron beam moving with a speed of $2.5\times 10^{7}ms^{-1}$  enters into the magnetic field directed perpendicular to its direction of motion. The magnetic induction of the field is $4\times 10^{-3}  wb/m^2$. The intensity of the electric field applied so that the electron remains undeflected due to the magnetic field is.

  1. $10^{4}N/C$

  2. $10^{5}N/C$

  3. $10^{7}N/C$

  4. $10^{3}N/C$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For no deflection
VB = E
$\rightarrow E = 2.5*10^7*4*10^{-3}$
$= 10*10^4$
$= 10^5 {N}/{C}$

Multiple choice deflection of electron beam by magnetic field observing the force and electron beam tubes charged particles electromagnetic forces physics

J.J. Thomson's cathode-ray tube experiment demonstrated that:

  1. cathode rays are streams of negatively charged ions

  2. all the mass of an atom is essentially in the nucleus

  3. the e/m of electrons is much greater than the e/m of protons

  4. the e/m ratio of the cathode ray particles changes when a different gas is placed in the discharge tube
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

(A) is the correct option. Since, in Thomson's first experiment, he discovered the cathode rays and the change they deposited were intrinsically linked together. In the second experiments, he discovered that the cathode ray were negative. He deducted that the cathode rays were made up of negatively charged particles.

Multiple choice deflection of electron beam by magnetic field observing the force and electron beam tubes charged particles electromagnetic forces physics

A particle of mass $1\times 10^{-26} \ kg $ and charge $1.6\times 10^{-19} \ C$ travelling with a velocity $1.28\times 10^6 \ m/s$ along the positive $X$-axis  enters a region in which a uniform electric field $\vec E$ and a uniform magnetic field of induction $\vec B$ are present. if $\vec E=-102.4 \times 10^3 \ \hat k \ NC^{-1}$ and $\vec B=8 \times 10^{-2} \ \hat j \ Wbm^{-2}$, the direction of motion of the particles is 

  1. along the positive X-axis

  2. along the negative X-axis

  3. at $45^{O}$ to the positive X-axis

  4. at $135^{O}$to the postive X-axis
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Write Force
F = q(vXB) + qE.
F =0N.
Hence the particle will continue moving towards positive X-axis.

Multiple choice deflection of electron beam by magnetic field observing the force and electron beam tubes charged particles electromagnetic forces physics

A proton and an $\alpha$ particle enter a magnetic field in a direction perpendicular to it. If the force acting on the proton is twice that acting on the $\alpha$- particle, the ratio of their velocities is

  1. $4 : 1$

  2. $1 : 4$

  3. $1 : 2$

  4. $2 : 1$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

We know that Force $(F _m)$ on a particle with charge "q" moving with a velocity of v at an angle $\theta$ to the magnetic field $(B)$ can be expressed as

$F _m=qvB \sin{\theta}$
Given, $\cfrac{F _m (p)}{F _m(\alpha)}$=2
$q _{\alpha}=2 \times q _{p}$
$\Rightarrow \ \cfrac{q _{p}v _pB}{q _{\alpha}v _{\alpha}B}=2$
We get 
$\cfrac{v _{p}}{v _{\alpha}}=4$