Moving Charges and Magnetism Class 12 Physics MCQs Pdf
61. An electron and a proton moving with the same speed enter the same magnetic field region at right angles to the direction of the field. For which of the two particles will the radius of circular path be smaller? [HOTS]
Answer/Explanation
Answer:
Explaination:
As r = \(\frac{mv}{qB}\) for same v and B r ∝ \(\frac{m}{q}\).
Since \(\frac{m}{q}\) is smaller for an electron, the radius of the circular
path followed by the electron will be smaller.
62. A proton and an electron travelling along parallel paths enter a region of uniform magnetic field, acting perpendicular to their paths. Which of them will move in a circular path with higher frequency? [CBSE 2018]
Answer/Explanation
Answer:
Explaination:
Electron
Reason:
Thus electron will move in circular path with higher frequency.
63. Write the expression for the magnetic moment of a circular coil of area A carrying a current I, in a vector form. [Foreign 2014]
Answer/Explanation
Answer:
Explaination:
M\(\vec{M}=\overrightarrow{I A}\), as vector \(\vec{A}\) is perpendicular to the
surface, the magnetic moment M will also be perpendicular to the plane of
circular coil.
64. Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid. Why?
Answer/Explanation
Answer:
Explaination:
At the edges of a solenoid, the field lines get diverged due to other fields or
non-availability of dipole loops, while in a toroid, the dipoles (in loops)
orient continuosly.
65. Using the concept of force between two infinitely long parallel current carrying conductors, define one ampere of current. [A1 2014]
Answer/Explanation
Answer:
Explaination:
One ampere is that amount of current which when flows through two thin
infinitely long straight conductors kept parallel to each other at 1 m distance
produces a force per unit length of magnitude 2 × 107 N/m.
66. Which has greater resistance
(a) milliammeter or ammeter
(b) milliammeter or voltmeter?
Answer/Explanation
Answer:
Explaination:
(a) Milliammeter
(b) Voltmeter
67. A voltmeter, an ammeter and a resistance are connected in series with a battery. The voltmeter gives same deflection but the deflection of ammeter is almost zero. Explain why?
Answer/Explanation
Answer:
Explaination:
When a voltmeter is connected in series, the current in the circuit decreases
because the resistance of voltmeter is high. Therefore, it will show some
deflection. But in an ammeter, the majority of this current will pass through
the shunt and a very small fraction will pass through the galvanometer.
68. State the law used to determine the direction of magnetic field at the centre of current carrying circular coil.
Answer/Explanation
Answer:
Explaination:
The right-hand thumb rule gives the direction of magnetic field which is stated
as under:
Curl the palm of your right hand around a circular wire with the fingers,
pointing in the direction of the current and the right hand thumb gives the
direction of magnetic field.
69. A narrow beam of protons and deuterons, each having the same momentum, enters a region of uniform magnetic field directed perpendicular to their direction of momentum. What would be the ratio of the radii of the circular paths described by them? [Similar Delhi 2019, Foreign 2011]
Answer/Explanation
Answer:
Explaination:
70. Write two properties of a material used as a suspension wire in a moving coil galvanometer.
Answer/Explanation
Answer:
Explaination:
(i) Low value of k (torsional constant), (ii) High conductivity.
71. A charged particle enters into a uniform magnetic field and experiences an upward
force as indicated in the figure. What is the charge sign on the particle?
Answer/Explanation
Answer:
Explaination:
72. How does the magnetic moment of an electron in a circular orbit of radius r and moving with a speed v change, when the frequency of revolution is doubled?
Answer/Explanation
Answer:
Explaination:
As M ∝ v, the magnetic moment also gets doubled, when the frequency of
revolution is doubled.
73. A current carrying loop is free to turn in a uniform magnetic field B. Under what
conditions, will the torque acting on it be
(i) minimum and
(ii) maximum?
Answer/Explanation
Answer:
Explaination:
T = MB sin θ
(i) Torque is minimum when the area vector of the loop and the magnetic field
vector are in the same direction, i.e. A\\B.
(ii) Torque is maximum when ALB.
74. Write two factors by which voltage sensitivity of a galvanometer can be increased.
Answer/Explanation
Answer:
Explaination:
As we know that \(V_{s}=\left(\frac{N A B}{k}\right) \frac{1}{R}\)
Thus, (i) Resistance should be less.
(ii) Torsional constant should be less.
75. An ammeter and a milliammeter are converted from the same galvanometer. Out of the two, which current measuring instrument has higher resistance? [HOTS]
Answer/Explanation
Answer:
Explaination:
The higher is the range, the lower will be the value of shunt, so a milliammeter
will be having higher resistance.
76. What is the advantage of using radial magnetic field in a moving coil galvanometer? [HOTS] [Delhi 2019]
Answer/Explanation
Answer:
Explaination:
(i) Maximum torque is experienced.
(ii) Current is directly proportional to the deflection.
(iii) The plane of the coil is parallel to the direction of magnetic field.
77. Why is it necessary for voltmeter to have a high resistance?
Answer/Explanation
Answer:
Explaination:
Since voltmeter is to be connected across two ends of a conductor in parallel,
if it has high resistance, then only a very small part of current will pass
through, and it will not affect the actual potential difference to be measured.
78. What is figure of merit of a galvanometer? [DoE]
Answer/Explanation
Answer:
Explaination:
Figure of merit is defined as the amount of current which produces unit
deflection in the galvanometer.
79. Define gyromagnetic ratio.
Answer/Explanation
Answer:
Explaination:
It is the ratio of the magnetic dipole moment to the angular momentum of the
electron revolving round the nucleus.
80. Can we decrease the range of an ammeter?
Answer/Explanation
Answer:
Explaination: will become negative, which is not possible.