Daily Olympiad: Physics - Magnetic Effects Current [20260511] – 5 Practice Problems & Printable PDF

1. A very long straight conductor carries a current I. A point P lies at a perpendicular distance d from the conductor. What is the magnitude of the magnetic field at point P?

A. μ₀I/(2πd) B. μ₀I/(4πd) C. μ₀I/(πd) D. Zero

Solution

Correct: A

The magnetic field around a long straight conductor is given by Ampere’s Law: B = μ₀I/(2πd). This is derived by considering a circular Amperian loop around the wire. Incorrect options often result from missing constants or misapplying the formula.

2. Two long parallel conductors carry currents I₁ and I₂ in opposite directions. The forces on them are:

A. Attractive B. Repulsive C. Zero D. Depend on the relative current magnitudes

Solution

Correct: B

Parallel currents in opposite directions produce repulsive forces. This follows from the right-hand rule for each wire's field and the force on the other wire. A common mistake is confusing directions based on the right-hand or left-hand rule.

3. A circular loop of radius R carries current I. At the center, the magnetic field due to an infinitesimal segment of the loop is perpendicular to the plane of the loop. What is the direction of the net magnetic field?

A. Along the axis of the loop B. Radially inward C. Radially outward D. Zero because of symmetry

Solution

Correct: A

Using the right-hand rule, each segment of the loop contributes a magnetic field perpendicular to the plane. The vector sum is along the axis (perpendicular), as only the axial components add constructively. Radial components cancel out due to symmetry.

4. A rectangular coil with 100 turns, each of area 0.01 m², is placed in a uniform magnetic field of 0.5 T. If a current of 2 A flows and the coil rotates such that its normal makes a 30° angle with the field, what is the maximum torque?

A. 5 N·m B. 10 N·m C. 0.5 N·m D. 0.25 N·m

Solution

Correct: C

Torque τ = N I A B sinθ = 100 * 2 * 0.01 * 0.5 * sin(30°) = 0.5 N·m. The maximum torque occurs at θ = 90°, but since the question specifies 30°, calculations must apply the sine factor correctly. Misreading θ or missing N leads to other options.

5. A charge particle of mass m and charge q moves in a magnetic field with velocity v perpendicular to the field. Which of these does NOT affect the particle’s orbital radius?

A. Velocity magnitude B. Charge magnitude C. Magnetic field strength D. Mass of the particle

Solution

Correct: D

The orbital radius r = mv/(qB). Velocity, charge, and magnetic field directly affect r, but mass does not appear in the formula. This is a common misconception; students often think mass affects radius during motion calculations.

Daily Olympiad: Physics - Magnetic Effects Current [20260511]

1. A very long straight conductor carries a current I. A point P lies at a perpendicular distance d from the conductor. What is the magnitude of the magnetic field at point P?

2. Two long parallel conductors carry currents I₁ and I₂ in opposite directions. The forces on them are:

3. A circular loop of radius R carries current I. At the center, the magnetic field due to an infinitesimal segment of the loop is perpendicular to the plane of the loop. What is the direction of the net magnetic field?

4. A rectangular coil with 100 turns, each of area 0.01 m², is placed in a uniform magnetic field of 0.5 T. If a current of 2 A flows and the coil rotates such that its normal makes a 30° angle with the field, what is the maximum torque?

5. A charge particle of mass m and charge q moves in a magnetic field with velocity v perpendicular to the field. Which of these does NOT affect the particle’s orbital radius?

Related Practice Tests

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