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PUCET (Punjab) Moving Charges and Magnetism — practice questions

Explore 48 free Moving Charges and Magnetism questions in PUCET (Punjab) 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 1–30 of 48.

A circular coil of radius $R$ carries current $I$. The magnetic field at the centre of the coil is:Read the answer and worked solution →Magnetic field is measured in:Read the answer and worked solution →Biot Savart law gives magnetic field due to a current element. It states dB is proportional to:Read the answer and worked solution →The magnetic force on a charge q moving with velocity v in field B:Read the answer and worked solution →A current-carrying wire of length L in magnetic field B experiences force:Read the answer and worked solution →Ampere's law states the line integral of B around a closed loop equals:Read the answer and worked solution →A magnetic dipole moment of a current loop is:Read the answer and worked solution →Magnetic field at center of a circular loop of radius R carrying current I:Read the answer and worked solution →Magnetic field inside a long solenoid (n turns per unit length, current I):Read the answer and worked solution →Magnetic field at distance r from a long straight current-carrying wire:Read the answer and worked solution →A charged particle of charge q, mass m enters magnetic field B perpendicular to velocity v. It follows a:Read the answer and worked solution →Torque on a current loop (moment m) in uniform field B:Read the answer and worked solution →In a velocity selector, electric field E and magnetic field B are perpendicular. Velocity of particles passing undeflected:Read the answer and worked solution →Magnetic field on the axis of a circular loop at distance x from center:Read the answer and worked solution →Magnetic flux through a surface is:Read the answer and worked solution →Cyclotron frequency for a charged particle in magnetic field B:Read the answer and worked solution →A solenoid of 200 turns, length 0.5 m, carries 2 A. Find magnetic field inside (μ₀ = 4π × 10⁻⁷):Read the answer and worked solution →A charged particle moves in a circle of radius 2 cm in a 1 T magnetic field with speed 4 × 10⁶ m/s. Mass-to-charge ratio m/q:Read the answer and worked solution →For a current loop in a non-uniform magnetic field, net force is zero only if:Read the answer and worked solution →Earth's magnetic field is approximately 50 μT. Force on a 1 m wire carrying 10 A perpendicular to field:Read the answer and worked solution →A toroid with 1000 turns and average radius 10 cm carries 0.5 A current. Field inside:Read the answer and worked solution →Two parallel wires carrying currents in OPPOSITE directions:Read the answer and worked solution →A magnetic dipole of moment m in field B has potential energy: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 Lorentz forceRead the answer and worked solution →Work done by a magnetic forceRead the answer and worked solution →Reading the Lorentz forceRead the answer and worked solution →Force on a current wireRead the answer and worked solution →The current carrying conductorRead the answer and worked solution →

Worked practice questions

A circular coil of radius $R$ carries current $I$. The magnetic field at the centre of the coil is:

  1. $B = \dfrac{\mu_0 I}{2\pi R}$
  2. $B = \mu_0 I R$
  3. $B = \dfrac{\mu_0 I}{2 R}$
  4. $B = \dfrac{\mu_0 I}{4\pi R}$
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Correct answer: C. $B = \dfrac{\mu_0 I}{2 R}$

From Biot-Savart's law applied to a circular loop of radius $R$ carrying current $I$, the field at the loop's centre is $B = \dfrac{\mu_0 I}{2 R}$. Direction along the axis of the loop. Right-hand rule again — curl fingers along current, thumb gives field direction. The field along the axis at distance $x$ from the centre is $B(x) = \dfrac{\mu_0 I R^2}{2(R^2 + x^2)^{3/2}}$, which collapses to the centre formula when $x = 0$.

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Magnetic field is measured in:

  1. newton
  2. coulomb
  3. tesla
  4. henry
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Correct answer: C. tesla

SI unit of magnetic field B is tesla (T) = 1 N/(A m) = 1 kg/(A s²). **Old unit gauss:** 1 T = 10⁴ G. Earth's field is about 50 μT.

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Biot Savart law gives magnetic field due to a current element. It states dB is proportional to:

  1. I dl × r / r³
  2. I × r
  3. dl / r²
  4. I × dl
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Correct answer: A. I dl × r / r³

We have dB = (μ₀ / 4π) × (I dl × r̂ / r²). So dB = (μ₀ / 4π) × (I dl × r / r³). Direction by right-hand rule (cross product of dl and r).

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