Question 1

Field around a current-carrying conductor: Which rule should be used to determine the circular direction of magnetic lines of force surrounding a straight conductor carrying conventional current?

Accepted Answer

Introduction / Context: Predicting magnetic field direction is necessary when laying out conductors, diagnosing electromagnetic interference, and understanding actuator behavior. Rules of thumb provide quick directionality without vector calculus. Given Data / Assumptions: Straight conductor with conventional current (positive to negative). We are interested in the azimuthal field direction encircling the wire. Standard sign conventions apply. Concept / Approach: The right-hand rule for a straight conductor states: point the right thumb in the direction of conventional current; the curl of the fingers gives the direction of magnetic field lines around the wire. Lenz’s law predicts the direction of induced currents opposing change in flux, and Faraday’s law relates induced emf to rate of change of flux linkage—neither directly gives the static field direction around a current-carrying wire. Some left-hand rules apply to motors (Fleming’s), not to this field direction case. Step-by-Step Solution: Identify we need the encircling field direction due to a straight current.Apply the right-hand rule: thumb = current direction; curled fingers = field direction.Conclude the rule is the right-hand rule.Select the corresponding option. Verification / Alternative check: Biot-Savart and Ampère’s law yield the same azimuthal field direction; the right-hand rule is their mnemonic counterpart. Why Other Options Are Wrong: Lenz’s law / Faraday’s law: Concern induction phenomena, not static field direction. Left-hand rule: Used for motor force directions or electron flow conventions, not this case. Common Pitfalls: Mixing up which hand/rule applies to motors versus fields, or to induction versus current-generated fields. Final Answer: the right-hand rule

Question 2

Flux density calculation in magnetics: Given a magnetic flux of 9 µWb uniformly distributed through a cross-sectional area of 5 × 10^–3 m^2, compute the flux density B and choose the correct value.

Accepted Answer

Introduction / Context: Flux density B quantifies how much magnetic flux passes through a given area and is crucial for core design, sensor calibration, and avoiding saturation in magnetic components. This problem practices converting micro-units and applying the fundamental relation B = phi / A. Given Data / Assumptions: Total flux, phi = 9 µWb = 9 × 10^–6 Wb. Area, A = 5 × 10^–3 m^2. Uniform flux distribution across the stated area. Concept / Approach: The definition of flux density is B = phi / A. After computing in SI units (Wb and m^2), express the result in tesla and convert to more convenient microtesla if appropriate. Careful unit handling prevents order-of-magnitude mistakes. Step-by-Step Solution: Write formula: B = phi / A.Insert values: B = (9 × 10^–6) / (5 × 10^–3).Compute: 9/5 = 1.8 and 10^–6 / 10^–3 = 10^–3, so B = 1.8 × 10^–3 T.Convert to microtesla: 1.8 × 10^–3 T = 1.8 mT = 1800 µT. Verification / Alternative check: Check magnitude: Micro-webers over milli-square-meters gives milli-tesla range, which matches 1.8 mT. Unit consistency confirms the calculation. Why Other Options Are Wrong: 555.56 T: Off by orders of magnitude; would require enormous flux or tiny area. 9 µT: Would correspond to 9 × 10^–6 Wb spread over 1 m^2, not 5 × 10^–3 m^2. 5 × 10^–3 T: Equals 5 mT, not supported by the numbers. Common Pitfalls: Mishandling micro (10^–6) and milli (10^–3) prefixes; forgetting to divide by area; mixing up webers and tesla definitions. Final Answer: 1800 µT

Question 3

Ferromagnetism basics: Ferromagnetic materials (such as iron and nickel) exhibit many tiny internal regions that align under a magnetic field. These regions are called magnetic ________.

Accepted Answer

Introduction / Context: Ferromagnetism arises from interactions at the atomic and microscopic levels. Understanding magnetic domains explains phenomena like hysteresis, saturation, and why bulk materials can hold magnetization once external fields are removed. Given Data / Assumptions: We consider common ferromagnetic materials (iron, cobalt, nickel, and certain alloys). The question targets the name for small internally magnetized regions. Concept / Approach: Magnetic domains are microscopic regions where atomic magnetic moments are largely aligned. In an unmagnetized specimen, domains are randomly oriented, canceling net magnetization. Under an applied field, domain walls move and domains grow in the field direction, producing macroscopic magnetization. Domain behavior underlies hysteresis and retentivity. Step-by-Step Solution: Recall that internal aligned regions in ferromagnets are called domains.Connect domain growth and rotation with magnetization processes.Choose “domains” from the options.Confirm the other choices do not match the standard term. Verification / Alternative check: Micromagnetic models and experimental imaging (e.g., Kerr microscopy) directly observe domain structures and wall motion in ferromagnets. Why Other Options Are Wrong: Flux lines: A field visualization concept in space, not internal material regions. Forces: Too generic; not the accepted term. Tapes: Unrelated; perhaps confused with magnetic recording tape, which itself relies on domains in a coating. Common Pitfalls: Confusing external field lines with internal microstructure; forgetting domain wall motion vs domain rotation mechanisms. Final Answer: domains

Magnetism and Electromagnetism Questions