Question 4

  • Eddy current brake

    However, unlike electro-mechanical brakes, in which the drag force used to stop the moving object is provided by friction between two surfaces pressed together, the drag force in an eddy current brake is an electromagnetic force between a magnet and a nearby conductive object in relative motion, due to eddy currents Eddy current brake - Wikipedia https://en.wikipedia.org/wiki/Eddy\_current\_brake

    C:\\266298A5\\73477446-49B2-471B-AFDD-BCD03931DCDD\_files\\image568.png

    Disc (wnduaive) Permanent magnet

  • Eddy

    ed•dy / edé/ O . a circular movement of water, counter to a main current, causing a small whirlpool. synonyms: swirl, whirlpool, vortex, maelstrom •small eddies at the rivers edge• . (of water, air, or smoke) move in a circular way. •the mists from the river eddied around the banks• synonyms: swirl, whirl, spiral, wind, circulate, twist; More Translations, word origin, and more definitions

Question 9

  • Magnetic Field due to a Current Loop

    Uh = CIP

    Bfor a Curved Wire Segment Find the field at point O due to the wire segment land R are constants vol 47TR Owill be in radians ds

    B for a Circular Loop of Wire • Consider the previous result, with a full circle 277 47Ta • This is the field at the center of the loop

Question 10

  • Energy in a capacitor

    Energy in a Capacitor In Prelecture 7 we calculated the work done to move charge Q from one plate to another: +Q -Q 1/2QV 1/2Q2/C Since Q vc This is potential energy waiting to be used... Electricity & Magnetism Lecture 8, Slide 14

Question 21

11 :3E0 21. A negatively charged particle initially in region I, as shown above, is accelerated from rest by an electric field of magnitude Eo between two parallel plates separated by a distance d. The particle then enters region 11, the space between two parallel plates with a separation 2d and an electric field of magnitude 3E0 in the opposite direction. How far into region Il does the particle travel before reversing direction? EON (B) 2 3 2

Question 22

22. A student wants to construct an inductor of a given inductance using copper wire and a plastic iEifGfficient supply of copper wire is available, the student will also need a A meterstick onl (B) secondary co and a meterstick (C) resistor of known resistance and a meterstick on (D) voltmeter and a meterstick (E) voltmeter andaDCpowerSUPPIY and F

  • Formula for inductance of simple solenoids

    Where, L = Inductance of coil in Henrys N — Number of turns in wire coil (straight wire = 1 — Permeability of core material (absolute, not relative) Relative permeability, dimensionless (go=l for air) 1.26 x 10-6 T-m/At permeability of free space Area of coil in square meters = Ttr2 A Average length of coil in meters

  • Derivation

    As the current in a coil of wire increases or decreases — aka, changes — the flux through the coil changes as well. This changing flux induces a back emf in the same coil. Since the change in flux is proportional to the change in the current, and opposes that change, we can write the relationship Ai At where L, the inductance, represents a proportionality constant that reflects the coil's geometry. Inductance is measured in a unit called a Henry (H) which is a V sec/amp or J sec2/C2. The most common inductor is a solenoid. Let's derive an expression for its inductance. An induced emf can be written as Ai or S — —L— At At Setting these two expressions equal to each other, yields Ai -L At At As the current changes from zero to l, the flux changes from zero to f, therefore Df= f and Di = I and our expression becomes BA A ,uonNA 10 A

    Notice that this expression, as predicted, deals only with the geometry of the solenoid: its cross-sectional area, length, and total number of coils. i-E/R 0.63i When an inductor is part of a circuit, the current does not instantaneously reach its maximum value of I = e/R, instead the current builds gradually depending on the ratio of L/R.

Question 23

23. Correct statements about a constant magnetic field acting on a charged particle include which of the following? I. The field can accelerate the particle. Il. The field can change the kinetic energy of the particle. Ill. The field can do positive work on the particle. A Ioni (B) 111 only (C) 1 and only (D) 11 and 111 only

Magnetic Field and Work \*Magnetic force is always perpendicular to velocity Therefore B field does no work\! •Why? Because AK = F = F • (FAt) = 0 \*Consequences • Kinetic energy does not change • Speed does not change Only direction changes Particle moves in a circle (if LB ) PHY2049: Chapter 28

Question 28

It 28. Two long, straight, current-carrying wires are parallel to each other in the plane of the page and separated by a distance a, as shown above. The direction of the current I in each wire is toward the top of the page. Which of the following best represents the force per unit length acting on the wires? (A) A repulsive force of magnitude //2za (B) A repulsive force of magnitude gol 2ma (C) An attractive force of magnitude g012 //2za (D) An attractive force of magnitude 27ta (E) zero If = zuoL' F —2

Question 29

29. A negatively charged rod is brought near a metal object on an insulating stand, as shown above. When charges stop moving, the left side of the object has an excess of positive charge, and the right side of the object, where the radius of curvature is less, has an excess of negative charge. Which of the following best describes the &ÉEjc potential on the metal object? (A) It is greatest on the positively charged side of the object. (B) It is greatest on the negatively charged side of the object. eatest at the cen o •ect. (D) It is the same everywhere on the Object. lnéffffom'théfiilfötination cannot given.

E lec+r/c / / 5 /;ac/epengevt4 o//Sfn or (KQv„ple: e erN-tre me {-41 bal t

Figure 25.20 An arbitrarily shaped conductor carrying a posi- tive charge. When the conductor is in electrostatic equilibrium, all of the charge resides at the surface, E = 0 inside the conduc- tor, and the direction Of E just outside the conductor is perpen- dicular to the surface. The electric potential is constant inside the conductor and is equal to the potential at the surface. Note from the spacing of the plus signs that the surface charge density is nonuniform.

Question 30

Four identical charged particles, each with charge Q, are fixed in place in the shape of an equilateral pyramid with sides of length L, as shown above. 30. What is the electrical potential energy of this 477 eo 2 3 (C) 4TE0 4 4ÆEo 6 (E) 47teo 23

Question 31

31. One of the four charged particles is released and allowed to move away under the influence of the electrostatic force from the other three charges. How much kinetic energy will it have when it is very far away? 4meo L (B) 47760 L 4 6 (E) 41teo 13±18/ +

Question 33

33. Two identical capacitors, X and Y, are connected in series across a battery. A dielectric material with K = 5 is placed in capacitor equilibrium is reached, how do the potential differences across the two capacitors and their charges compare? Sevies Some Potential Pifference (A) (D) Charge Qx > Qy Qx=Qy Qx>Q 67

Series The same charge is on each capacitor. V = Ice q) Ceq= Cl

Parallel Now the charges are not the same. But the voltages

tot = Ql +Q2 + Q3 - CIAV + C2AV + C3AV = (Cl + + C3)AV Qeq = (Ceq)AV

Question 35

35. When a square wire loop of side d carrying current I is in a uniform magnetic field of magnitude B in the position shown above, there is a torque on the loop. The magnitude of this torque is (A) directly proportional to d ( ) inversely proportlonal to d (D) inversely proportional to d2 (E) independent of d Il MAGNETISM SECTION I

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