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Physics Exam 2
Fichas del conjunto (51)
- 1Electric circuit-energy is transferred from a source (like a battery pack) to a device (MP3 player) by charges that move through a conducting wire
-the battery can be used to provide electrical current to a circuit
-(+) is always longest plate while (-) is smaller (capacitor has equal plates) - 2Electron transfers with terminalsWithin a battery, a chemical reaction occurs that transfers electrons from one terminal (leaving it +) to another terminal (leaving it -)
The maximum electrical potential difference across the terminals = electromotive force (emf; voltage) of the batter (potential difference between battery is somewhat less than max value indicated by emf - 3Electric currentThe flow of charges; the amount of charge per unit time that passes through a surface that is perpendicular to the motion of the charges (more charges moving through increases current)
- 4DC vs ACDirect current: if the charges move around the circuit in the same direction at all times (constant, same charges per second, stable, rare)
Alternating current: if the charges move first one way then the opposite (fluxuating, direction changes positive to negative, sin function graph, plugs in home, too fast for naked eye) - 5Conventional current-hypothetical flow of positive charges that would have the same effect in the circuit as the movement of negative charges that actually does occur (don't use electron flow)
-(+) which is longest to (-) which is shortest - 6Resistance definition-the resistance R is defined as the ratio of the voltage applied across a piece of material to the current I through the material (how hard to move through)
-resistance is ohm (volt/amphere) / omega symbol
V = IR - 7Ohm's LawV = IR
- 8Battery and current relationshipgreater battery (voltage) = greater current ( I proportional to V)
- 9Length and diameter relationship with resistancelonger (length) and narrower (diameter) offer higher resistance, smaller flow rates
high resistance = weak current = high voltage - 10Resistor-to the extent that a wire or an electrical device offers resistance to electrical flow (bulb filament is a resistor in form of a thin piece of wire that becomes hot enough to emit light)
-zig zap line represents a resistor - 11Resistance and area relationshipsmaller area = greater resistance
- 12Temperature and resistivityin metals, an increase in temperature increases resistivity (conductors)
Reverse for semiconductors
Metals have small resistivities while rubber has large and semiconductors have intermediate
Resistivity is ohm*meter - 13Two things resistance depends onDepends on the resistivity and geometry of the material
- 14Electric power-watts (only positive, because voltage and current are both positive or both negative)
-when there is current in a circuit as a result of a voltage, the electric power delivered to the circuit is P = electrical energy/Time
-when a charge goes from higher to lower, it loses electric potential energy (decrease in potential energy must be accompanied by transfer of that energy; i.e. cell phone and light/sound/heat energy)
-gains electric potential if lower to higher (from chemical energy stored in battery) - 15V = V0sin(2pift)Set calculator to radians
- 16Series wiring-Series wiring means that the devices are connected in such a way that there is the same electrical current through each device
-if current interrupted in one than in other too
-Rs = R1+R2
-the voltage across all resistors in series is sum of the individual voltages (current for parallel)
-total power of any # of resistors in series is equal to power delivered to the equivalent resistance (same for parallel) - 17Parallel Wiring-parallel wiring means devices are connected in such a way that the same voltage is applied across each device
-each receives current from the battery as if other is not present (not affected if one is interrupted)
-electrical appliance plugged into wall socket, the appliance is connected in parallel with others
-1/Rp = 1/R1 + 1/R2
-smallest resistance has the largest impact in determining equivalent resistance (if one approchaes 0, eq. resis. approaches 0; near 0 resistances short out others) - 18Internal resistance-batteries and generators add some resistance to a circuit, this resistance is internal resistance
-cause the voltage between terminals to drop below maximum value (emf), the actual voltage is known as terminal voltage - 19Kirchoff's RulesIf no 2 resistors are in series or parallel this can help
-The junction rule: the total current directed into a junction must equal the total current directed out of the junction (sum of the magnitude of currents directed into a junction equals sum out)
Loop rule: expresses the conservation of energy in terms of the electrical potential and states that for a closed-circuit loop, the total of all potential rises is the same as the total of all potential drops (around any closed circuit loop, the sum of potential drops = sum of potential rises) - 20Loop rule drop vs rise(+) to (-) = potential drop
(-) to (+) = potential rise
steps
1. draw current (if incorrect direction, current (I) will be negative)
2. mark resistors with (+) and (-). outside a batter, conventional current is always directed from a higher potential to lower - 21Ammeter-measures current
-must be inserted into the circuit so that the current passes through it
-ideal ammeter should have zero resistance because the equivalent resistance of ammeter adds to circuit resistance which increasing circuit resistance decreases current - 22Voltmeter-connected between points, not inserted into the circuit like ammeter
-ideally, voltage registered by the voltmeter should be the same that exists when the voltmeter is not connected, however, voltmeter takes some current from circuit (ideal has infinity/very large resistance) - 23Capacitors in series and parallel-in parallel, same voltage different charge (Cp=C1+C2..)
-all capacitors in series regardless of their capacitance contain charges at the same magnitues (equal charge because it passes by induction from one to next)
1/Cs=1/C1+1/C2... - 24RC circuitsresistor-capacitor circuit (ex. heart pacemakers/windshield)
Capacitor charging: time Constance is the amount of time for the capacitor to accumulate 63.2% of its equilibrium charge
-charge approaches equilibrium fast when the time constant is small
Capacitor discharging: the amount of time to lose 63.2% if the charge (smaller = discharge faster)
Charing and discharing have different q equations - 25Magnetism definespin of the electrons around themselves not the atom
- 26Magnetic field-B (unit is tesla T); vector
-the surrounding magnet is a magnetic field, its direction at any point in space is the direction indicated by the north pole of a small compact needle placed at that point - 27magnet materialiron, nickel, or combination
- 28Needle of compasspermanent magnet that has north magnetic pole at one end and south magnetic pole at other
- 29Poles-possible to separate (+) and (-) charge but not north and south poles (no magnetic monopole)
-like repel, unlike attract - 30Magnetic field lines-originate from north, end on south
-don't stop midspace
-strength is proportional to # of lines per unit area that passes through a surface oriented perpendicular to the lines
-field lines closer = stronger
-magentic field at any point is tangent to the magnetic field line at that point
-iron filling align themselves along field lines - 31North magnetic pole and geographical-north pole of compass needle points northward, not exactly the north geographical pole because of geo. pole is that point where earth's axis of rotation
-north magnetic pole is not fixed/moves
-earth's magnetic field lines are not parallel to surface at all points, near north magnetic pole the field lines are perpendicular (the angle that the magnetic field makes with respect to the surface at any point is known as the angle of dip) - 32Conditions that must be met for a charge to experience a magnetic force when placed in a magnetic field
- 33Right-hand rule number 1extend the right-hand s0 the fingers point along the direction of the magnetic field (B) and the thumb points along the velocity of the charge. The palm of hand then faces the direction of the magnetic force (F) that acts of positive charge (opposite predicted by RHR1 if negative)
Thumb will be current I for a wire carrying a current - 34Charged particle in a magnetic field-deflected upward instead of sideways like electric field
-as charge moves upward the direction of the magnetic force changes, always remaining perpendicular to both magnetic field and velocity - 35Magnetic force and work-unlike electrical force, magnetic force cannot do work on a charged particle or change the kinetic energy or speed
-magnetic force always acts in direction that is perpendicular to the motion of the charge (velocity; directed toward center of the circular path) - 36What increases radiushigh velocity for charge or decrease in magnetic field
-stronger fields = tighter circular paths - 37Mass spectrum-determine relative masses and abundance of isotopes (physicist)
-the mass spectrum of naturally occurring neon shows 3 isotopes because different number of neutrons (different abundances) - 38Current carrying wire-find the direction of the magnetic force on a moving charge or wire carrying current I
-a magnet applies a force to a wire carrying a current (I), the wire will move and be subject to magnetic force
-magnetic force on current-carrying wire is a maximum when wire is perpendicular to field (angle=90), vanishes when parallel or antiparallel (angle 0 or 180) - 39Torque on a current-carrying coil-if a loop is suspended properly, in a magnetic field, the magnetic force produces a torque that tends to rotate the loop
-greater magnetic moment of a current-carrying coil, greater torque could experience when placed in magnetic field - 40Current carrying wire and magnetic fieldcan produce its own magnetic field
- 41Right-hand rule number 2-curl the fingers of the right hand into the shape of a half-circle. (curled fingers placed at center of loop)
-thumb in direction of conventional current (I)
-tips of fingers will point in direction of megentic field (B) - 42Solenoid
- 43Ampere's Law-relationship between electric current and magnetic field that is creates
-for any current geometry that produces a magnetic field that does not change in time - 44Magnetism produced by electrons in atom can arise from two motions1. each e- orbiting the nucleus behave like atomic-sized loop of current that creates small magnetic field
2. each e- possesses a spin that also gives rise to magnetic field
net magnetic field = combo of 1 and 2
In most substances, magnetism at an atomic level tend to cancel out with result that the substance is nonmagnetic overall - 45FerromagnetismWhen magnetism at an atomic level isn't canceled out for groups of 10^16-10^19 neighboring atoms because they have electron spins that are naturally aligned parallel to each other (ferromagnetic materials)
common: iron, nickel, cobalt, chromium dioxide, and alnico (aluminium, nickel, cobalt) - 46Magnetic domain-ferromagnetic materials result in small but highly magnetized regions (0.01-0.1 nm)
-own north and south poles - 47Induced magnetism-randomly arranged ferromagnetic material magnetic fields of domains cancel out (little to no magnetism)
-unmagnetized piece of iron can be magnetized by placing an external magnetic field provided by a permanent magnet or electromagnet
-explains permanent magnet sticks to fridge or electromagnet picking up scrap iron; aluminum and copper can't be induced (antiferromagnetic materials) and consequently magnets do not stick to them - 48Induced state of magnetism in iron (how)-domains with parallel magnetism or nearly parallel to external magnetic field grow at expense of other domains
-magnetic alignment of some domains may rotate and become oriented in direction of external field - 49Chromium dioxide and induced magnetism-cassette tapes
-domain remain aligned and magnetized permanently even with external magnet removed - 50Magnetism induced in the ferromagnetic field vs. externalMagnetism induced in the ferromagnetic field can be large even with external field (not unusual for induced to be much stronger than external)
- 51Whenever current in a wire reverses directionthe force exerted on the wire by a given magnetic field also reverses direction
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- College Physics II Fichas sobre Physics Exam 2, creado por Bree Bree el 12/03/2022.
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