Class 12 Moving Charges And Magnetism CBSE Questions & Answers

Class 12 · Moving Charges And Magnetism

This is Physics Class 12 Moving Charges and Magnetism CBSE Questions & Answers. There are 15 questions in this test with each question having around four answer choices.

Questions & Answers

1
A beam of electrons at rest is accelerated by a potential V. This beam experiences a force F in a uniform magnetic field. The accelerating potential is changed to V’ and the force experienced by the electrons in the same magnetic field is 2F. The ratio V/V’ is
  • A
    1.0
  • B
    1/2
  • C
    1/4
    Correct
  • D
    2.0
2
Two infinitely long wires carry currents in opposite directions. Then the field at a point P lying midway between them is
  • A
    zero
  • B
    half of the field due to each wire alone
  • C
    square of the field due to each wire alone
  • D
    twice the field due to each wire alone
    Correct
3
A wire of given length is first bent in one loop and the next time it is bent in three loops. If the same current is passed in both the cases, the ratio of the magnetic field induction at their centres will be
  • A
    1:4
  • B
    1:3
  • C
    9:1
  • D
    1:9
    Correct
4
A proton (charge + e coul) enters a magnetic field of strength B (Tesla) with speed v, parallel to the direction of magnetic lines of force. The force on the proton is
  • A
    evB/2
  • B
    evB
  • C
    zero
    Correct
  • D
    \(\alpha \)
5
A uniform electric field and a uniform magnetic field are produced, pointed in the same direction. An electron is projected with its velocity pointed in the same direction
  • A
    the electron will turn to its right
  • B
    the electron velocity will decrease in magnitude
    Correct
  • C
    the electron will turn to its left
  • D
    the electron velocity will increase in magnitude
6
A wire is perpendicular to the plane of the paper. A ring of compass needles surrounds the wire in the plane of the paper with center of ring being the center of the wire .Initially there is no current in the wire. What happens after a steady dc current is established in the wire?
  • A
    some needles become parallel to each other while others are uneffected
  • B
    The needles become parallel to each other
  • C
    The needles become tangential to the ring of which they are a part
    Correct
  • D
    nothing happens
7
A wire of length L carrying current i is placed perpendicular to the magnetic induction B. The total force on the wire is
  • A
    iB/L
  • B
    iLB
    Correct
  • C
    LB/i
  • D
    iL/B
8
A steel wire of length l has a magnetic moment M. It is then bent into a semicircular arc. The new magnetic moment is
  • A
    \({\rm{M }} \times {\rm{ l}}\)
  • B
    M
  • C
    M / l
  • D
    $\frac{{2M}}{\pi }$
    Correct
9
What is magnetic induction at point O, if the current carrying wire is in the shape given in the figure?
Question 9 figure 1
  • A
    \(\frac{\mu_o i}{4\pi r}{[\frac{\pi}{2}+1 ]}\)
  • B
    \(\frac{\mu_o i}{4\pi r}\)
  • C
    \(\frac{\mu_o i}{4\pi r}\).\(\frac{2\pi}{2}\)
  • D
    \(\frac{\mu_o i}{4\pi r}{[\frac{3\pi}{2}+1 ]}\)
    Correct
10
A wire is bent in the form of a circular arc with a straight portion AB. If the current in the wire is i, find magnetic induction at O.
Question 10 figure 1
  • A
    \(\frac{\mu_o i}{4\pi r}\) \(\left( {{\rm{tan}}\theta } \right)\)
  • B
    \(\frac{\mu_o i}{4\pi r}\) \(\left( {\pi - \theta + {\rm{tan}}\theta } \right)\)
    Correct
  • C
    \(\frac{\mu_o i}{4\pi r}\) \(\left( {\pi - \theta } \right)\)
  • D
    \(\frac{\mu_o i}{4\pi r}\) \(\left( {\pi - {\rm{tan}}\theta } \right)\)
11
A long wire is bent into a circular loop and long straight wires on either side but there being no contact at point P. If current i enters at Q and leaves at R, then what is magnetic induction at O.
Question 11 figure 1
  • A
    \(\frac{\mu_o i}{2 r}\)[\(\frac{1}{\pi}\)+1 ]
    Correct
  • B
    \(\frac{\mu_o i}{2 r}\)
  • C
    \(\frac{\mu_o i}{2 r}\)[1-\(\frac{1}{\pi}\) ]
  • D
    \(\frac{\mu_o i}{2\pi r}\)
12
The magnetic field at the centre of the circular coil carrying current of 4A is
Question 12 figure 1
  • A
    \({\rm{2}}\pi {\rm{ }} \times {\rm{1}}{0^{ - {\rm{4}}}}{\rm{T}}\)
  • B
    \(\frac{8\pi}{3}\) \( \times {\rm{1}}{0^{ - {\rm{4}}}}{\rm{T}}\)
  • C
    \(\frac{8\pi}{3}\) \( \times {\rm{1}}{0^{ - {\rm{5}}}}{\rm{T}}\)
  • D
    \({\rm{2}}\pi {\rm{ }} \times {\rm{1}}{0^{ - {\rm{5}}}}{\rm{T}}\)
    Correct
13
An infinitely long straight conductor is bent into the shape as shown in fig. The magnetic induction at the centre of circular loop is
Question 13 figure 1
  • A
    \(\infty\)
  • B
    \(\frac{\mu_o i}{2\pi r}\) \(\left( {\pi + {\rm{1}}} \right) \)
  • C
    \(\frac{\mu_o i}{2\pi r}\) \(\left( {\pi - {\rm{1}}} \right) \)
    Correct
  • D
    zero
14
In the fig given below magnetic induction at the point O is
Question 14 figure 1
  • A
    \(\frac{\mu_o I}{4\pi r}\)
  • B
    \(\frac{\mu_o I}{4r}\)+\(\frac{\mu_o I}{2\pi r}\)
  • C
    \(\frac{\mu_o I}{4r}\).\(\frac{\mu_o I}{4\pi r}\)
  • D
    \(\frac{\mu_o I}{4r}\)+\(\frac{\mu_o I}{4\pi r}\)
    Correct
15
A wire of given length is first bent in one loop and then in three loops. If same current is passed in both cases, the ratio of magnetic inductions at the centre will be
  • A
    1 : 4
  • B
    1 : 3
  • C
    1 : 9
    Correct
  • D
    9 : 1