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ISC Class 12 Moving Charges and Magnetism — practice questions — page 2

Explore 133 free Moving Charges and Magnetism questions in ISC Class 12 Physics. Open each question or exercise to read its content, reference answers and available explanation.

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Moving Charges and Magnetism questions and exercises with answers

Showing questions 31–60 of 133.

On the axis of a circular current loop of radius R, at a distance x ≫ R, the magnetic field can be written in terms of the moment m as:Read the answer and worked solution →In a moving coil galvanometer the magnetic field is made radial chiefly so that:Read the answer and worked solution →A moving coil galvanometer is converted into an ammeter by connecting:Read the answer and worked solution →The current sensitivity of a moving coil galvanometer (deflection per unit current) is:Read the answer and worked solution →In a galvanometer, the number of turns N is doubled (so resistance also doubles). The voltage sensitivity then:Read the answer and worked solution →Spot the Lie: Magnetism (ISC 12)Read the answer and worked solution →Match each current to its fieldRead the answer and worked solution →Judge these claims on magnetic forceRead the answer and worked solution →The current sensitivity of a moving coil galvanometer with N turns, coil area A, magnetic field B, spring constant k isRead the answer and worked solution →What the cyclotron frequency ignoresRead the answer and worked solution →A long straight wire carries $5$ A. The magnetic field $0.10$ m away from the wire is:Read the answer and worked solution →Depends on speed or notRead the answer and worked solution →A proton of mass m, charge e, speed v enters a magnetic field B perpendicular to its velocity. The radius of its circular path isRead the answer and worked solution →A rectangular current loop is placed in a uniform magnetic field. The net force on the loop isRead the answer and worked solution →A 0.5 m wire carrying 2 A is placed perpendicular to a 0.4 T magnetic field. The force on the wire isRead the answer and worked solution →At equilibrium, the deflection ϕ of a moving coil galvanometer with N turns, area A, current I, in a radial magnetic field B and spring constant k satisfiesRead the answer and worked solution →A 0.1 m radius loop carries 5 A. The magnetic field at a point on its axis 0.1 m from the centre is approximately (μ₀ = 4π × 10⁻⁷ T·m/A)Read the answer and worked solution →Symbol to quantityRead the answer and worked solution →Currents make fieldsRead the answer and worked solution →Two long parallel wires carry currents in the same direction. They willRead the answer and worked solution →A positive charge moves with velocity $\vec{v}$ PARALLEL to a uniform magnetic field $\vec{B}$. The magnetic force on it isRead the answer and worked solution →The magnetic field at the CENTRE of a circular current loop of radius $R$ carrying current $I$ isRead the answer and worked solution →A current loop of area $A$ carrying current $I$ has a MAGNETIC MOMENT of magnitudeRead the answer and worked solution →A charged particle moves with velocity v parallel to a uniform magnetic field B. The magnetic force on the particle isRead the answer and worked solution →A circular loop of radius R carries current I. The magnitude of the magnetic field at its centre isRead the answer and worked solution →The angular frequency of a particle of charge q and mass m moving in a cyclotron with magnetic field B isRead the answer and worked solution →The magnetic field inside an ideal long solenoid with n turns per unit length carrying current I isRead the answer and worked solution →In a crossed E and B velocity selector, a charged particle of speed v passes undeflected when v equalsRead the answer and worked solution →The magnetic field inside a toroidal solenoid with N total turns, mean radius r, carrying current I isRead the answer and worked solution →The period of revolution of a charged particle moving in a uniform magnetic field perpendicular to its velocity isRead the answer and worked solution →

Worked practice questions

On the axis of a circular current loop of radius R, at a distance x ≫ R, the magnetic field can be written in terms of the moment m as:

  1. (μ₀/4π)(2m / x²)
  2. (μ₀/4π)(m / x³)
  3. (μ₀/4π)(2m / x³)
  4. (μ₀/2π)(m / x³)
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Correct answer: C. (μ₀/4π)(2m / x³)

1. Axial field: $B = \dfrac{\mu_0 I R^2}{2(x^2+R^2)^{3/2}}$. 2. For $x \gg R$, drop $R^2$: $B \approx \dfrac{\mu_0 I R^2}{2x^3}$. 3. Using $m = I\pi R^2$, write $B = \dfrac{\mu_0 m}{2\pi x^3}$. 4. Rearranged: $B = \dfrac{\mu_0}{4\pi}\dfrac{2m}{x^3}$, the axial dipole form. _Source: syllabus Physics Ch 4 "Moving Charges and Magnetism", p.155_

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In a moving coil galvanometer the magnetic field is made radial chiefly so that:

  1. The deflection stays proportional to current
  2. The coil resistance is greatly reduced
  3. The spring constant becomes much larger
  4. The current required is greatly increased
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Correct answer: A. The deflection stays proportional to current

1. The torque on the coil is $\tau = NIAB\sin\theta$ in general. 2. A radial field keeps the plane of the coil always along B, so $\theta = 90^\circ$ and $\sin\theta = 1$. 3. The torque then reduces to $NIAB$, independent of deflection angle. 4. Balancing with $k\phi$ gives $\phi \propto I$, a linear, easily-read scale. _Source: syllabus Physics Ch 4 "Moving Charges and Magnetism", p.159_

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A moving coil galvanometer is converted into an ammeter by connecting:

  1. A small resistance in series
  2. A large resistance in series
  3. A large resistance in parallel
  4. A small resistance in parallel
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Correct answer: D. A small resistance in parallel

1. An ammeter must carry large current yet barely disturb the circuit, so it needs very low resistance. 2. Connecting a small shunt resistance $r_s$ in parallel diverts most of the current around the coil. 3. The combined resistance becomes small (≈ $r_s$ when $R_G \gg r_s$). 4. A series large resistance would instead make a voltmeter, so that option is wrong. _Source: syllabus Physics Ch 4 "Moving Charges and Magnetism", p.160_

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