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TAMU PHYS 208 - Test 3 review

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Ch. 28- The force acting on a charged particle moving with velocity through a magnetic field is always perpendicular to v and B.- If a charged particle moves through a region containing both an electric field and a magnetic field, it can be affected by both an electric force and a magnetic force.- If the fields are perpendicular to each other, they are said to be crossed fields. - If the forces are in opposite directions, a particular speed will result in no deflection of the particle.- When a uniform magnetic field B is applied to a conducting strip carrying current i, with thefield perpendicular to the direction of the current, a Hall-effect potential difference V is set up across the strip. - The electric force FE on the charge carriers is then balanced by the magnetic force FB onthem.- A charged particle with mass m and charge magnitude moving with velocity v perpendicular to a uniform magnetic field B will travel in a circle. - Various magnetic forces act on the sections of a current carrying coil lying in a uniform external magnetic field, but the net force is zero.- The Hall Effect: When a conducting strip carrying a current i is placed in a uniform magnetic field,some charge carriers (with charge e) build up on one side of the conductor, creating a potential difference V across the strip. The polarities of the sides indicate the sign of the charge carriers.Ch. 29- Curled–straight right-hand rule: Grasp the element in your right hand with your extended thumbpointing in the direction of the current. Your fingers will then naturally curl around in the direction of the magnetic field lines due to that element.- Parallel wires carrying currents in the same direction attract each other, whereas parallel wires carrying currents in opposite directions repel each other.- To find the force on a current-carrying wire due to a second current-carrying wire, first find the field due to the second wire at the site of the first wire. Then find the force on the first wire due to that field.- Curl your right hand around the Amperian loop, with the fingers pointing in the direction of integration. A current through the loop in the general direction of your outstretched thumb is assigned a plus sign, and a current generally in the opposite direction is assigned a minus sign.- The magnetic field just outside of a solenoid is zero.Ch. 30- Faraday’s Law 1. A current appears only if there is relative motion between the loop and the magnet (one mustmove relative to the other); the current disappears when the relative motion between them ceases. 2. Faster motion produces a greater current. 3. If moving the magnet’s north pole toward the loop causes, say, clockwise current, then moving the north pole away causes counterclockwise current. Moving the south pole toward or away from the loop also causes currents, but in the reversed directions.- An emf is induced in the loop at the left in Figs. 30-1 and 30-2 when the number of magnetic field lines that pass through the loop is changing.-1 weber=1 Wb=1 T ∙ m2 - The magnitude of the emf ʓ induced in a conducting loop is equal to the rate at which the magnetic flux φB through that loop changes with time.- Here are the general means by which we can change the magnetic flux through a coil: 1. Change the magnitude B of the magnetic field within the coil. 2. Change either the total area of the coil or the portion of that area that lies within the magnetic field (for example, by expanding the coil or sliding it into or out of the field). 3. Change the angle between the direction of the magnetic field and the plane of the coil (for example, by rotating the coil so that field is first perpendicular to the plane of the coil and then isalong that plane).- Lenz’s Law: An induced current has a direction such that the magnetic field due to the current opposes the change in the magnetic flux that induces the current.- A changing magnetic field produces an electric field.- Electric potential has meaning only for electric fields that are produced by static charges; it has no meaning for electric fields that are produced by induction.-1 henry=1 H=1 T ∙ m2/ A .- An induced emf ʓL appears in any coil in which the current is changing.- Initially, an inductor acts to oppose changes in the current through it. A long time later, it acts like ordinary connecting wire.- Speaking anthromorphically, The coil wants to fight the changes, so if the current is already goingto the right, than to produce an induced electric field, the current must be decreasing.Ch. 31- LC Circuit:1. The maximum values of UE and UB are both Q2 /2C. 2. At any instant the sum of UE and UB is equal to Q2 /2C, a constant. 3. When UE is maximum, UB is zero, and conversely- Whatever the natural angular frequency ω of a circuit may be, forced oscillations of charge, current, and potential difference in the circuit always occur at the driving angular frequency ωd.- RLC Circuit:XL>XC: The circuit is said to be more inductive than capacitive. φ is positive for such a circuit, which means that phasor I rotates behind phasor ʓm .XC>XL: The circuit is said to be more capacitive than inductive. φ is negative for such a circuit, which means that phasor I rotates ahead of phasor ʓm.XC=XL: The circuit is said to be in resonance, a state that is discussed next. Φ=0o for such a circuit, which means that phasors ʓm and I rotate together.Ch. 32- Diamagnetism is exhibited by all common materials but is so feeble that it is masked if the material also exhibits magnetism of either of the other two types. In diamagnetism, weak magnetic dipole moments are produced in the atoms of the material when the material is placedin an external magnetic field; the combination of all those induced dipole moments gives the material as a whole only a feeble net magnetic field. The dipole moments and thus their net fielddisappear when is removed. The term diamagnetic material usually refers to materials that exhibit only diamagnetism. o A diamagnetic material placed in an external magnetic field develops a magnetic dipole moment directed opposite. If the field is nonuniform, the diamagnetic material is repelled from a region of greater magnetic field toward a region of lesser field. (levitating frog)- Paramagnetism is exhibited by materials containing transition elements, rare earth elements, and actinide elements (see Appendix G). Each atom of such a material has a permanent resultantmagnetic


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