Analysis of Force Equation

Q. 34. A uniform circular ring of mass 3 kg and radius 20 cm is rotating about an axis passing through its diameter with an angular speed of 200 rpm with the help of a motor. When the motor is switched off, calculate the torque that must be applied to the ring to bring it to rest in 20 revolutions.

Q. If a charged particle at rest experiences no electromagnetic force then,

1. Electric field cannot be zero.
2. Magnetic field must be zero
3. Electric and magnetic field both must be non-zero
4. Magnetic field may or may not be zero.

Q. An electron is moving along positive x axis. To get it moving on an anticlockwise circular path in the x-y plane a, magnetic field is applied - a) along positive y axis b) along positive z Axis c) along negative y axis d) along negative z axis

Q. An electron beam projected along positive x-axis experiences a force due to magnetic field along positive y-axis. What is the direction of magnetic field?

Q. an electron is moving along +x direction. to get it moving along anticlockwise circular path in x-y plane, magnetic field applied along?

Q. Give examples where force is perpendicular to displacement and hence work done is zero.

Q. A charged particle passes undeviated through velocity vector if, v =particle velocity, E= Electric Field, B= Magnetic Field

1. v<E/B
2. v>E/B
3. v=E/B
4. None of these

Q. A particle with ${10}^{-11}$ coulomb of charge and ${10}^{-7}$ kg mass is moving with a velocity of ${10}^8$ m/s along the y-axis. A uniform static magnetic field B = 0.5 T is acting along the x-direction. The force on the particle is

1. $5\times {10}^{-11}Nalong\hat{i}$
2. $5\times {10}^{3}Nalong\hat{k}$
3. $5\times {10}^{-11}Nalong\hat{j}$
4. $5\times {10}^{-4}Nalong-\hat{k}$

Q. A metallic block carrying current i is subjected to a uniform magnetic induction B as shown in the figure. The moving charges experience a force F given by ……. which results in the lowering of the potential of the face …….? Assume the speed of the carriers to be v.

1. $eVB\hat{k},ABCD$
   
2. $eVB\hat{k},ABCD$
3. $-eVB\hat{k},ABCD$
   
4. $-eVB\hat{k},EFGH$

Q. An electron moves with speed $2\times {10}^{5}m/s$ along the positive x-direction in the presence of a magnetic induction $B=\hat{i}+4\hat{j}-3\hat{k}$ (in Tesla.) The magnitude of the force experienced by the electron in Newton's is (charge on the electron = $1.6\times {10}^{-19}$ C)

1. $1.18\times {10}^{-13}$ N
   
2. $1.28\times {10}^{-13}$ N
   
3. $1.6\times {10}^{-13}$ N
   
4. $1.72\times {10}^{-13}$ N

Q. A metallic block carrying current i is subjected to a uniform magnetic induction B as shown in the figure. The moving charges experience a force F given by ……. which results in the lowering of the potential of the face …….? Assume the speed of the carriers to be v.

1. $eVB\hat{k},ABCD$
   
2. $eVB\hat{k},ABCD$
3. $-eVB\hat{k},ABCD$
   
4. $-eVB\hat{k},EFGH$

Q. A proton is moving in a field of induction $[2\overrightarrow{i}+4\overrightarrow{j}]T$ with velocity $[3\times {10}^7\overrightarrow{i}]m{s}^{-1}$. The force experienced by it will be?

1. $16.8\times {10}^{-12}(+\hat{k})N$
2. $6\times {10}^{-7}(-\hat{k})N$
3. $12\times {10}^{-7}(+\hat{k})N$
4. $0$

Q. For a positively charged particle moving in a x-y­ plane initially along the x-axis, there is a sudden change in its path due to the presence of electric and/or magnetic fields beyond P. The curved path is shown in the x-y plane and is found to be non-circular. Which one of the following combinations is possible

1. $\overrightarrow{E}=0;\overrightarrow{B}=b\hat{i}+c\hat{k}$
   
2. $\overrightarrow{E}=ai,\overrightarrow{B}=c\hat{k}+a\hat{i}$
   
3. $\overrightarrow{E}=0;\overrightarrow{B}=c\hat{j}+b\hat{k}$
   
4. $\overrightarrow{E}=ai,\overrightarrow{B}=c\hat{k}+b\hat{j}$

Q. The force experienced by a particle of charge q moving with a velocity v in a uniform magnetic field B is given by
$\overrightarrow{F}=q(\overrightarrow{V}\times \overrightarrow{B})$
Statement I: The vectors F and V are perpendicular to each other
Statement II: The vectors V and B can have any angle between them
Statement III: The vectors F and B are perpendicular to each other

1. All the statements are true
2. Statement I and II are true only
3. Statement I and III are true only
4. Statement II and III are true only

Q. A charge particle having charge q is accelerated through a potential difference V and then it enters a perpendicular magnetic field in which it experiences a force F. If V is increased to 5V, the particle will experience a force

1. $F$
2. $5F$
3. $\frac{F}{5}$
4. $\sqrt{5}F$

Q. What is the density of neutron star ?

1. none
2. $6.87\times {10}^{6}kg{m}^{-3}$
3. $5.46\times {10}^{12}kg{m}^{-3}$
4. $2.42\times {10}^{17}kg{m}^{-3}$

Q. An electron is fired parallel to uniform Electric and Magnetic field acting in the same direction.Electron

1. Gains Energy
2. Loses Energy
3. Moves along a circular path
4. Moves along parabolic path