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 -


    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

  • 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

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

results matching ""

    No results matching ""