PHYS 104

Relative to the vacuum value, a dielectric always A. increases the capacitance. B. decreases the capacitance. C. doubles the capacitance. D. leaves the capacitance unchanged.

A

When charging a capacitor in an RC circuit, you expect A. the current to decrease with time. B. the current to stay constant. C. the current to increase with time.

A

A 8.45-μC particle with a mass of 6.15 x 10-5 kg moves perpendicular to a 0.493-T magnetic field in a circular path of radius 34.1 m. How much time will it take for the particle to complete one orbit? A. 92.7 s B. 0.0927 s C. 9.27 s D. 927 s

A *TIME= Distance/Velocity* Circular motion: *r=m𝒱/qB* r= radius m= mass 𝒱= velocity q= charge B= field

What is the magnitude of the magnetic force exerted on a 4.67-m length of wire carrying a current of 2.38 A perpendicular to a magnetic field of 0.385 T? A. 4.28 N B. 0.916 N C. 11.1 N D. 1.80 N

A Magnetic Force on current: *F=ILBSinθ* perpendicular: sin(90º)= 1

Consider the long, straight current-carrying wires shown in the figure. One wire carries a current I1 = 4.5 A in the positive x-direction; the other wire carries a current I2 = 3.2 A in the negative y-direction. Calculate the net magnetic field at point A. LOOK AT IMAGE ON HW QUIZ 5 (#3) A. 15 μT, into the page (-z-hat) B. 15 μT, out of the page (+z-hat) C. 2.6 μT, into the page (-z-hat) D. 2.6 μT, out of the page (+z-hat)

A Magnetic field straight wire: *B= µ₀I/2πr* µ₀= 4πE-7 r= distance I= current into the page because I₁ points right (thumb) but field points down to point A (fingers) so force is into page; I₂ pints down and field points left towards A so force is into page???

A circular coil of wire has a radius of 6.30 cm and has 215 turns of wire that carries 5.90 A of current. What is the magnetic field at the center of the coil? A. 12.7 mT B. 6.33 mT C. 58.8 μT D. 1 x 104 T

A Magnetic field, center of circular coil: *B=µ₀IN/2r* µ₀= 4πE-7 r= radius

Negative charges, when allowed to move, go towards regions where the electric potential is high. A. True B. False

A

By convention, the direction of an electric field at any point in space is determined by the direction of the electric force on a A. positive charge. B. neutral charge. C. negative charge.

A

If the amount of charge is fixed, a capacitor can store more energy when the voltage is larger. A. true B. false

A

In a Kirchoff loop, if the loop direction and current direction coincide for a resistor, the voltage is considered to be negative. A. True B. False

A

In a closed circuit, the movement of electrons is best described as A. basically random movement with a slow drift in the direction opposing the current. B. very fast straight-line motions in the direction of the current. C. basically random movement with a slow drift in the direction of the current. D. very fast straight-line motions in the direction opposing the current.

A

Kirchoff's loop theorem states that the sum of ALL potential differences (drops and sources) around a closed loop must be zero. A. True B. False

A

A parallel plate capacitor has plates with an area of 0.019 m2and a separation of 0.72 mm. The space between the plates is filled with a dielectric whose dielectric constant is 2.4. What is the potential difference between the plates when the charge on the capacitor plates is 5.8 μC? A. 1.0 x 104 V B. 1.0 x 10-4 V C. 2.4 x 104 V D. 1.0 x 107 V

A C=Kℰ₀A/D V=Q/C

Capacitance increases as A. the charge increases and/or the voltage decreases. B. the charge decreases and/or the voltage decreases. C. The charge increases and/or the voltage increases. D. the charge decreases and/or the voltage increases.

A C=Q/V

A charge of +3q sits at the origin. A charge of -5q sits on the x-axis at the 1.00 m mark. Given that q=4.11 x 10-9 C, at what location on the x-axis is the electric potential zero? A. 0.375 m B. 0.500 m C. 0.625 m D. 0.125 m

A ELECTRIC POTENTIAL due to point charge: V=Kq/r **(note: if it was asking for a third charge, it would be on the left side of the +3q but since it is asking for electric potential, it is found in the middle of the two) V(net)=V1+V2 (HW2)

A cell membrane is 8.7 nm thick and has an electrical resistivity of 1.3E7 Ωm. If the potential difference between the inner and outer surfaces of a cell membrane is 63 mV, how much current flows through a circular patch of membrane with radius 1.0 μm? A. 1.8 x 10-12 A B. 5.6 x 10-13 A C. 1.3 x 10-5 A D. 1.2 x 10-18 A

A I= V/R R= p(L/A) A=πr²

For a fixed voltage, you can increase the power by A. decreasing the resistance. B. increasing the resistance. C. not changing the resistance.

A P= V²/R

A portable CD player operates with a current of 20 mA at a potential difference of 6.2 V. What is the power usage of the player? A. 0.124 W B. 124 W C. 12.4 W D. 0.124 V E. 1.24 V

A P=IV

A three-way lightbulb can produce 30 W, 50 W, or 75 W of power at 60 V. What is the resistance of the lightbulb in the 75 W case? A. 48 ohms B. 60 ohms C. 1.25 ohms D. 75 ohms

A P=IV P=I²R

A 100-W lightbulb operates on a potential difference of 120 V. Find the resistance of the bulb. A. 144 Ω B. 12 Ω C. 120 Ω D. 0.007 Ω

A P=I²R=V²/R

An aluminum wire is 1.3 m long and has a diameter of 0.05 cm. What is the resistance of the wire? A. 0.18 Ω B. 0.045 Ω C. 9.0 x 10-5 Ω D. 2.65 x 10-8 Ω E. 5.3 x 10-5 Ω

A R=p(L/A)

A proton has an initial speed of 4.90E5 m/s. What potential difference is required to bring the proton to rest? A. 1250 V B. -1250 V C. 2.00 x 10-16 V D. -2.00 x 10-16 V E. zero

A conservation of energy equation: *1/2mv²(initial)-1/2mv²(final)= |qℯ|(∆V)*

Three resistors with values of 7.5 ohms, 9.0 ohms, and 20 ohms are connected in series in a circuit with a 12-volt battery. What is the current in each resistor? A. current in resistor 1=0.33 A, current in resistor 2=0.33 A, current in resistor 3=0.33 A. B. current in resistor 1=3.5 A, current in resistor 2=3.5 A, current in resistor 3=3.5 A C. current in resistor 1=1.6 A, current in resistor 2=1.3 A, current in resistor 3=0.6 A D. current in resistor 1=1.6 A, current in resistor 2=1.6 A, current in resistor 3=1.6 A

A current and charge is the SAME in series R(eq)= R1+R2+R3 I=V/R

Determine the value of the potential 3.50 mm from the positive plate of a pair of parallel plates separated by 12.0 mm and connected to a 18.0-volt battery. A. 12.8 V B. 5.25 V C. 18.0 V D. 8.50 V

A draw it out: set the potential at the negative plate to be 0 and at the positive plate to be 18 and divide by the distance to find the difference in between (3.5 mm from the positive plate would also mean 8.5 mm from the negative plate)

A system of 1728 particles, each of which is either an electron or a proton, has a net charge of +3.552 x 10-17 C. What is the mass of this system? A. 1.629 x 10-24 kg B. 222.0 kg C. 1.574 x 10-27 kg D. 2.886 x 10-24 kg

A take the positive charge and convert to protons (1.6E-19C/per proton); this will give you EXCESS protons; subtract this from particles to give you the equal amount of protons and electrons; divide this by 2 to give you the amount of protons and the amount of electrons; add this amount to the excess protons to give you net protons; convert both to kg and add to give you mass of system

In a laboratory, two wires lay next to each other on a bench. Wire A is twice as long as wire B. An experiment causes the two wires to have the same current flowing through them. The wires both exist in the magnetic field of the Earth. Which of the following correctly describes the magnetic force magnitudes experienced by the wires? A. Wire A feels twice the force of wire B. B. Wire B feels twice the force of wire A. C. The wires feel the same force.

A the longer wire experiences GREATER force (think of long pipe vs small straw- which requires less force for the same current?

In a flashing neon light circuit, a time constant of 1.2 s is desired. If you have a 3.0 micro-farad capacitor, what resistance should you use in the circuit? A. 4.0x10^(5) ohms B. 4.0x10^(5) C. 3.6x10^(-6) ohms D. 2.5x10^(-6) ohms

A time constant= C x R

When resistors are connected in parallel, the currents through each resistor A. are different with the largest current flowing through the smallest resistor. B. are all equal. C. are zero in all resistors but one. D. are different with the largest current flowing through the largest resistor.

A • parallel= same voltage; series= same charge and current

Capacitors connected in series... (Choose ALL answers that are correct) A. act like one capacitor with an inverse capacitance equal to the sum of the inverses of the individual capacitances. B. must have the same voltages. C. act like one capacitor with a capacitance equal to the sum of the individual capacitances. D. must have the same charges.

A & D *series= inverse capacitance and same charges; parallel= add capacitance and same voltage*

A 9.0-V battery is connected across the terminals A and B for the group of resistors shown in the figure. What is the potential difference across R2? Diagram #1 HW 4 A. 3.6 V B. 9.0 V C. 5.4 V D. 1.8 V

A.

A glass rod rubbed with silk acquires a charge of +7.0x10^(-9) C. How much mass is transferred from the rod? A. 4.0x10^(-20) kg B. 4.4x10^(10) C. -4.0x10(-20) kg D. 4.0x10^(-20)

A.

Electric field lines are drawn parallel to equipotentials. A. true B. false

A.

What is the equivalent resistance in the following arrangement of resistors? (R1=3.0 ohms, R2=3.0 ohms, R3=4.0 ohms, R4=4.0 ohms) Diagram #2 HW 4 A. 1.5 ohms B. 14 ohms C. 2.9 ohms D. 0.9 ohms

A.

Two point charges, the first with a charge of +4.47 x 10-6 C and the second with a charge of +1.86 x 10-6 C, are separated by 17.4 mm. What is the magnitude of the electrostatic force experienced by charge 2? A. 247 N B. 2.47 x 10-4 N C. 103 N D. 2.74 x 10-8 N

A. Fnet= Kq₁q₂/r²

The resistor in an RC circuit has a resistance of 110 Ω and a time constant of 1.9 ms. Calculate the current in the circuit 7.6 ms after the switch is closed. Assume that the capacitor is initially uncharged and that the emf of the battery is 12.0 V. A. 2 mA B. 110 mA C. 27.5 mA D. 40 mA

A. use charging equation: *I=∆V/R • e^(-t/𝒯)*

An object with a charge of +6.3 μC and a mass of 0.073 kg experiences an upward electric force, due to a uniform electric field, equal in magnitude to its weight. If the electric charge on the object is reduced by one-third while its mass remains the same, find the direction and magnitude of its acceleration. A. down at 6.5 m/s2 B. up at 4.9 m/s2 C. up at 9.8 m/s2 D. down at 4.9 m/s2 E. up at 6.5 m/s2 F. down at 9.8 m/s2

A. F(net)= ma --> *F(electric)-F(gravity)= ma* E= F/q --> E= ma/q *FORCE Electric= Electric field x Q* new applied equation: 1/3Eq-mg= ma --> 1/3q (ma/q) - mg= ma --> -2/3mg= ma --> solve for a

If the distance between two equal positive charges doubles, A. the magnitude of the electric force decreases by a factor of 4. B. The magnitude of the electric force increases by a factor of 4. C. the magnitude of the electric force does not change. D. the magnitude of the electric force decreases by a factor of 2.

A. F= kq₁q₂/r²

Two point charges lie on the x axis. A charge of -2.3 x 10-6 C is at x=-5 cm, and a charge of +9.2 x 10-6 C is at x=12 cm. At what position x would a third positive charge be in equilibrium? A. x=-22 cm B. x=+22 cm C. x=0 cm D. x=-17 cm E. x=+17 cm

A. draw this out and see where it would make sense to put on the x axis; it would make sense to put near the smaller negative charge so it experiences a strong pull towards the positive X axis and an equivalent push from the larger charge towards the -X axis F(total)= F1 - F2 (subtract F2 because it pushes the point charge towards the -X axis) F1=F2 F=Kq₁q₂/r²

Two objects with opposite charges are fixed in place (they cannot move). If the charge on the negative object doubles and the positive object's charge remains the same, A. then the force on both charges increases by a factor of 2. B. then the force doesn't change because the objects are fixed. C. only the force on the negative charge increases by a factor of 2. D. only the force on the positive charge increases by a factor of 2.

A. Electric force= charge x Electric field (F= Eq)

How are electric potential difference (voltage) and electric potential energy related? A. The voltage is the electric field value divided by a positive charge. B. The voltage is the potential energy per unit positive charge. C. There is no relationship. D. The potential energy is the voltage per unit positive charge.

B

If you want to create a working battery, which one of the following options MUST occur? A. There must be the same electric potential at each electrode. B. There must be a larger excess of electrons at one electrode than at the other. C. There must be no voltage between the electrodes. D. There must be equal numbers of electons at each electrode.

B

Magnetic fields can be caused by A. magnetic currents. B. electric currents. C. stationary charges. D. any moving object, regardless of charge.

B

If two current-carrying wires are placed parallel to one another, but the currents run in opposite directions, the wires will attract one another. A. true B. false

B The direction is obtained from the right hand rule. Note that two wires carrying current in the same direction attract each other, and they repel if the currents are opposite in direction.

If a current flows to the right in a wire that is in a magnetic field that points into your computer screen, the direction of the force on the wire is A. towards the bottom of the screen. B. towards the top of the screen. C. into the screen away from you. D. out of the screen towards you.

B right hand rule: thumb= current or velocity fingers= field palm= force

A 200-ohm resistor is placed in a circuit with four identical batteries connected in series. If the resistor draws 4.0 A, what is the terminal voltage of each battery? A. 1600 V B. 200 V C. 75 V D. 100 V

B * in circuit: CURRENT is conserved • V=IR 200 resistor/4 batteries= 50 resistor per battery • 50(R) x 4 (I)= V

If the potential increases most rapidly in the positive y-direction, the electric field points in the A. positive x-direction. B. negative y-direction. C. negative x-direction. D. positive y-direction.

B *****ELECTRIC FIELD AND ELECTRIC POTENTIAL POINT IN OPPOSITE DIRECTIONS***** ****electric field lines, point in the direction that a positive test charge would accelerate if placed upon the line.

A 6.0-volt battery is connected to a parallel plate capacitor with plate areas of 0.3 meters-squared each and a plate separation of 10 mm. How much energy is stored in the capacitor? A. 4.8x10^(-9) J B. 1.6x10^(-9) J C. 8.2x10^(-10) J D. 4.9x10^(-9)

B Energy storage: U=1/2QV=1/2CV²=Q²/2C

If the charge on a capacitor is doubled, the energy stored in the capacitor is A. unchanged. B. quadrupled. C. tripled. D. doubled.

B Energy stored: U=1/2QV=1/2CV²=Q²/2C

The rear window defogger on your car works by Joule heating - converting electrical energy to heat. If the current through those wires doubles, the heating power A. doubles. B. quadruples. C. stays the same. D. halves.

B P= I²/R

Two charges, +4.0 micro-C and +3.0 micro-C, are separated by a distance of 35 cm. What is the electric field halfway between the charges? A. 7.3x10^(4) N/C towards the +3.0 micro-C charge B. 2.9x10^(5) N/C towards the +3.0 micro-C charge C. 2.9x10^(11) N/C towards the +4.0 micro-C charge D. 2.9x10^(5) N/C

B POINT CHARGE: Enet= Kq1/.175² - Kq2/.175²

With a battery, direct currents can sometimes flow from the anode to the cathode, but at other times they flow in the opposite direction. A. True B. False

B electrons flow AROUND the circuit, toward the negative end inside the battery, pushed by the chemical reaction, and toward the positive end in the outside circuit, pushed by the electrical voltage *battery pushes - towards - (unfavorable) does work via voltage

An electron volt measures A. electric potential difference. B. energy. C. equipotential. D. electric field.

B equal to the energy gained by an electron(a charged particle carrying unit electronic charge) when the electrical potential at the electron increases by one volt.

An equipotential surface is A. The amount of work done in moving a charge. B. the set of locations where the electric potential is constant. C. The same as the direction of the electric field. D. always perpendicular to a charge distribution.

B equipotential surface consists of equipotential lines perpendicular to field lines where electric POTENTIAL is CONSTANT

In order to measure the current passing through a resistor, an ammeter should A. have a resistance equal to that of the resistor being measured B. be connected in series, or "in-line", with the resistor C. be connected in parallel, or "across", the resistor D. have a very large internal resistance

B line up in series bc current is the SAME in series

The magnetic force on a current-carrying wire is greatest when the current is A. parallel to the magnetic field direction. B. perpendicular to the magnetic field direction. C. at a 45-degree angle to the magnetic field direction. due to positive charges only.

B magnetic force is GREATEST when perpendicular to CURRENT

The resistivity and conductivity have no connection to each other. A. True B. False

B more resistance = less conductive

Find the current in resistor R3. Diagram #3 HW 4 A. 3.75 A B. 1.25 A C. 5.00 A D. 2.50 A

B.

The only way for an object to have an electric charge is to have an excess of electrons. A. True B. False

B.

An electrically neutral object (like a balloon): A. can be subjected to electric forces only if it gains a net negative charge. B. cannot be subjected to electric forces because it is neutral. C. can be subjected to electric forces due to polarization. D. can be subjected to electric forces only if it gains a net positive charge.

C

Electric fields are vector quantities. Which of the following descriptions is correct? A. Positive charges have electric field vectors that point TOWARDS the charge B. The sign of the charge has nothing to do with the field direction. C. Positive charges have electric field vectors that point AWAY FROM the charge. D. Negative charges have electric field vectors that point AWAY FROM the charge

C

The resistance in a conductor like copper increases with length because A. The electrons can be absorbed more easily. B. the electric force decreases with increasing distance. C. the electrons have more opportunity to bounce off of atoms and not participate in the overall flow. D. they have farther to go without colliding with atoms.

C

What is the voltage across ten 2.0 V batteries when they are connected in parallel? A. 20 V B. 10 V C. 2.0 V D. 5.0 V

C **PARALLEL= SAME voltage; series= same charge**

A 12-V battery is connected to four capacitors in series. The capacitors have the following capacitances: 9 μF, 12 μF, 32 μF, and 42 μF. Find the voltage across the 32 μF capacitor. A. 4 V B. 12 V C. 1.5 V D. 0.375 V

C 1/C(eq)= 1/C(1)+1/C(2)... C=Q/V

On average, an electric water heater (4.5 kW) operates for 1.5 hours each day. If the cost of electricity is $0.20/kWh, what is the cost of operating the heater during a 14-day period? A. $12.60 B. $0.90 C. $18.90 D. $40.50

C 4.5 kW x 1.5 hr= 6.75 kWh per day $.20/kWh x 6.75 kWh/day x 14 days

A 4.0-meter length of straight wire carries a current of 15 A in a uniform magnetic field of 500 micro-T whose field lines make an angle of 45-degrees with the current direction. Find the force on the wire. A. 2.1x10^(-2), perpendicular to the paper B. 3.0x10^(-2) N, parallel to the current direction C. 2.1x10^(-2) N, perpendicular to the paper D. 2.1x10^(-2) N, parallel to the magnetic field vector

C F= B•I•L•sinθ B= field I= current L= length

For a given circuit voltage and 10 resistors, which situation provides the largest circuit current? A. All of the resistors in series. B. Pairs of resistors alternating between series and parallel. C. All of the resistors in parallel. D. Half the resistors in series, half in parallel (order doesn't matter).

C parallel circuits: 1/R(eq)= 1/R1+1/R2+1/R3... parallel circuits have low R values so therefore would have high current: I=V/R

How would you connect multiple batteries in order to get the biggest possible voltage? a. It does not matter how you combine them. B. Put all of the batteries in parallel. C. Put all of the batteries in series. D. Put some in parallel and some in series.

C series= add voltage, whereas parallel has same voltage

In a parallel plate situation, the voltage is 60 V. If the electric potential value at the negative plate is 60 V, then A. the electric potential value at the positive plate is 0 V. B. the electric potential value at the positive plate is -60 V. C. the electric potential value at the positive plate is 120 V. D. the electric potential value at the positive plate is 60 V.

C voltage= overall or NET V; if the potential at the negative plate (which we usually see as 0) is 60, this means -60 and we need 120 to get an overall net 60

Kirchoff's junction theorem is a restatement of which of the following physical laws? A. Conservation of energy. B. Conservation of momentum. C. Conservation of charge. D. Conservation of mass

C • junction theorem states: he sum of the currents flowing into that junction is equal to the sum of the currents flowing out of that junction

An object with charge -Q is placed in an electrically neutral metal cup (without touching the cup). Which of the following best describes the situation? A. The electric field in the metal of the cup is defined by +Q, the charge in the metal is -Q, and there is no surface charge. B. The electric field in the metal of the cup is zero, the charge in the metal is -Q, and there is no surface charge. C. The electric field in the metal of the cup is zero, the charge in the metal is zero, and the surface charge is -Q. D. The electric field in the metal of the cup is defined by -Q, the charge in the metal is +Q, and there is no surface charge. E. The electric field in the metal of the cup is zero, the charge in the metal is zero, and the surface charge is +Q

C & E the electric field of a neutral object is ALWAYS neutral, even if a charged object is acting upon it, however, surface can be charged because the charged object pushes or pulls the electrons to the surface (even though the overall field is neutral); the surface near the charged object is +Q; the surface on the opposite side of the charged object is -Q

Two charges of +3.5 micro-C are placed at opposite ends of a meterstick. Where on the meterstick could a free proton be in electrostatic equilibrium? A. At either the 0 m or 1 m marks. B. At the 0.35 m mark. C. At the 0.5 m mark. D. Nowhere on the meterstick.

C. electrostatic equilibrium: excess charge has optimally distanced itself so as to reduce the total amount of repulsive forces (place where repulsion is lowest); it is exactly in the middle because the charges are the SAME in magnitude

For resistors in parallel, A. the currents through each resistor are equal. B. the current only flows through one resistor. C. the individual voltage drops across the resistors add up to the total voltage. D. the voltages across each resistor are equal.

D

If you are charging an initially uncharged capacitor in an RC circuit, the voltage of the capacitor A. starts at the battery voltage and decreases to zero. B. remains at zero always. C. always remains equal to the battery voltage. D. starts at zero and increases to the battery voltage.

D

In a parallel plate situation, the voltage is 60 V. If the electric potential value at the positive plate is 60 V, then A. the electric potential value at the negative plate is 60 V. B. the electric potential value at the negative plate is 120 V. C. the electric potential value at the negative plate is -60 V. D. the electric potential value at the negative plate is 0 V.

D

The resistance of something A. depends only on its geometry. B. depends only on its resistivity. C. Is a fundamental property of a material. D. depends on its resistivity and its geometry.

D

Imagine you are measuring the electric field of a negative point charge. When you place your field measuring instrument 1 m away from the charge you measure a magnitude of 2 N/C. What does your instrument read when you are 0.5 m away? A. 0.5 N/C. B. 2 N/C. C. 4 N/C. D. 8 N/C.

D E= Kq/r²

Object A has a net charge of +Q. Object B has a net charge of +2Q. A positive test charge is first brought 1 m from object A. Object A is removed and the same test charge is brought 1 m from object B. Which of the following correctly describes the relative magnitudes of the electric fields experienced by the test charge? A. The field due to object A is twice that due to object B. B. The field due to object A is four times that due to object B. C. The field due to object B is four times that due to object A. D. The field due to object B is twice that due to object A.

D E= Kq/r²

An ideal voltmeter A. can have any resistance value B. has zero resistance C. has infinite resistance.

D ideal ammeter has ZERO resistance ideal voltmeter has INFINITE resistance

A charged object is brought near a neutral electroscope. If the leaves separate, A. you know that the object is electrically neutral. B. you know that the object has a net negative charge. C. you know that the object has a net positive charge. D. you know that the object has a net electric charge.

D. * could be net positive or negative- just depends on what charge the object has (i.e. if the object had a net negative charge, it would cause negative electrons to disperse on the wings and be pushed further away)

In a physics lab, a student discovers that the magnitude of the magnetic field in a specific location near a long wire is 0.3 micro-T. If the wire carries a current of 10 A, what is the distance from the wire to that location? A. 0.15 m B. 6.7 m C. 0.67 m D. 0.25 m

b B=µ₀(I)/2πr B: magnetic field µ₀: 4πE-7 I: current

In order to measure the voltage drop due to a resistor in a circuit, a voltmeter should be A. connected in series, or "in-line", with the resistor B. connected only to the wire through which the current leaves the resistor C. connected to the battery or voltage source D. connected in parallel, or "across", the resistor.

d voltage is the SAME in parallel

how can you increase the magnetic field around a wire?

wrap the wire into a coil called a solenoid