Fill-in-the-Blank — Test Your Knowledge — Notes

Paragraph 1: Biot-Savart and Field Configurations

The Biot-Savart law states that the magnetic field due to a current element I dl at a point distance r away is given by dB = (1). The direction is determined by the (2) rule. For an infinitely long straight wire carrying current I, the field at perpendicular distance d is B = (3). At the centre of a circular loop of N turns, radius R, and current I, the field is B = (4). Inside a solenoid with n turns per unit length, the field is B = (5) and is (6) (uniform/non-uniform). Ampere's circuital law states that ∮B·dl = (7).

Answers: (1) (μ_{0}/4π)(I dl sinθ / $r^{2}$ ) | (2) right-hand | (3) μ_{0} $\frac{I}{2πd}$ | (4) μ_{0} $\frac{NI}{2R}$ | (5) μ_{0}nI | (6) uniform | (7) μ_{0} $I_{enc}$

Paragraph 2: Lorentz Force and Circular Motion

A charge q moving with velocity v at angle θ to magnetic field B experiences a force F = (1). This force is always (2) to the velocity, so the magnetic force does (3) work on the charge. When v is perpendicular to B, the charge moves in a circular path with radius r = (4). The time period of this circular motion is T = (5) and is (6) $\frac{dependent on}{independent of}$ the velocity. For helical motion, the pitch equals (7).

Answers: (1) qvB sinθ | (2) perpendicular | (3) no/zero | (4) $\frac{mv}{qB}$ | (5) 2π $\frac{m}{qB}$ | (6) independent of | (7) v_∥ × T = v cosθ × (2πm/qB)

Paragraph 3: Magnetic Materials

Materials in which all atoms have no net magnetic moment are called (1) and have susceptibility χ (2) zero. Materials with permanent atomic magnetic moments that don't interact strongly are called (3); they obey Curie's law χ = (4). Materials with strong exchange interactions and magnetic domains are called (5); above the (6) temperature, they become paramagnetic. The residual magnetism when H = 0 is called (7); the reverse field needed to reduce B to zero is called (8).