Phys202 Test 2

Front 1

The quantity (1/2)E0*E^2has the significance of:

Back 1

energy/volume

Front 2

Capacitors A and B are identical. Capacitor A is charged so it stores 4 J of energy and capacitorB is uncharged. The capacitors are then connected in parallel. The total stored energy in thecapacitors is now:

Back 2

2J

Front 3

To store a total of 0.040 J of energy in the two identical capacitors shown, each should have acapacitance of:

Back 3

1 uJ

Front 4

A battery is used to charge a parallel-plate capacitor, after which it is disconnected. Then theplates are pulled apart to twice their original separation. This process will double the:

Back 4

stored energy

Front 5

A parallel-plate capacitor has a plate area of 0.3m2and a plate separation of 0.1 mm. If thecharge on each plate has a magnitude of 5×10−6C then the force exerted by one plate on theother has a magnitude of about:

Back 5

5N

Front 6

A certain capacitor has a capacitance of 5.0μF. After it is charged to 5.0μC and isolated, theplates are brought closer together so its capacitance becomes 10μF. The work done by theagent is about:

Back 6

-1.25*10^(-6)

Front 7

A dielectric slab is slowly inserted between the plates of a parallel plate capacitor, while thepotential difference between the plates is held constant by a battery. As it is being inserted:

Back 7

the capacitance and the charge on the positive plate increase but the potential differencebetween the plates remains the same

Front 8

An air-filled parallel-plate capacitor has a capacitance of 1 pF. The plate separation is thendoubled and a wax dielectric is inserted, completelyfilling the space between the plates. As aresult, the capacitance becomes 2 pF. The dielectric constant of the wax is:

Back 8

4

Front 9

One of materials listed below is to be placed between two identical metal sheets, with no, airgap, to form a parallel-plate capacitor. Which produces the greatest capacitance?

Back 9

material of thickness 0.5 mm and dielectric constant 11

Front 10

Two capacitors are identical except that one isfilled with air and the other with oil. Bothcapacitors carry the same charge. The ratio of the electricfieldsEair/Eoilis:

Back 10

between 1 and infinity

Front 11

a parallel-plate capacitor, with air dielectric, is charged by a battery, after which the batteryis disconnected. A slab of glass dielectric is then slowly inserted between the plates. As it isbeing inserted:

Back 11

a force attracts the glass into the capacitor

Front 12

Two parallel-plate capacitors with the same plate separation but different capacitance areconnected in parallel to a battery. Both capacitors arefilled with air. The quantity that isNOT the same for both capacitors when they are fully charged is:

Back 12

charge on the positive plate

Front 13

Two parallel-plate capacitors with the same plate area but different capacitance are connectedin parallel to a battery. Both capacitors arefilled with air. The quantity that is the same forboth capacitors when they are fully charged is:

Back 13

potential difference

Front 14

Two parallel-plate capacitors with different plate separation but the same capacitance areconnected in series to a battery. Both capacitors arefilled with air. The quantity that is NOTthe same for both capacitors when they are fully charged is:

Back 14

electricfield between the plates

Front 15

Two parallel-plate capacitors with different capacitance but the same plate separation areconnected in series to a battery. Both capacitors arefilled with air. The quantity that is thesame for both capacitors when they are fully charged is:

Back 15

charge on the positive plate

Front 16

A car battery is rated at 80 A·h. An ampere-hour is a unit of:

Back 16

charge

Front 17

Current has units

Back 17

C/s

Front 18

Current has unit

Back 18

ampere

Front 19

The units of resistivity are:

Back 19

ohm-meter

Front 20

The rate at which electrical energy is used may be measured in

Back 20

watt

Front 21

Energy may be measured in

Back 21

watt-second

Front 22

Which one of the following quantities is correctly matched to its unit?

Back 22

Potential difference - J/C

Front 23

Current is a measure of:

Back 23

amount of charge that moves past a point per unit time

Front 24

A 60-watt light bulb carries a current of 0.5 A. The total charge passing through it in one houris:

Back 24

1800C

Front 25

A 10-ohm resistor has a constant current. If 1200 C of chargeflow through it in 4 minutes whatis the value of the current?

Back 25

15A

Front 26

Conduction electrons move to the right in a certain wire. This indicates that:

Back 26

he current density and electricfield both point left

Front 27

Two wires made of different materials have the same uniform current density. They carry thesame current only if:

Back 27

heir cross-sectional areas are the same

Front 28

A wire with a length of 150 m and a radius of 0.15 mm carries a current with a uniform currentdensity of 2.8×107A/m2. The current is:

Back 28

2A

Front 29

n a conductor carrying a current we expect the electron drift speed to be:

Back 29

much less than the average electron speed

Front 30

Two substances are identical except that the electron mean free time for substance A is twicethe electron mean free time for substance B. If the same electricfield exists in both substancesthe electron drift speed in A is

Back 30

twice that in B

Front 31

The current is zero in a conductor when no potential difference is applied because

Back 31

or every electron with a given velocity there is another with a velocity of equal magnitudeand opposite direction.

Front 32

The current density is the same in two wires. Wire A has twice the free-electron concentrationof wire B. The drift speed of electrons in A is:

Back 32

half that of electrons in B

Front 33

copper contains 8.4×1028free electrons/m3. A copper wire of cross-sectional area 7.4×10−7m2carries a current of 1 A. The electron drift speed is approximately:

Back 33

10−4m/s

Front 34

If J is the current density anddnAis a vector element of area then the integral$nJ·dnAover anarea represents:

Back 34

the current through the area

Front 35

If the potential difference across a resistor is doubled:

Back 35

only the current is doubled

Front 36

five cylindrical wires are made of the same material. Their lengths and radii arewire 1: lengthf, radiusrwire 2: lengthf/4, radiusr/2wire 3: lengthf/2, radiusr/2wire 4: lengthf, radiusr/2wire 5: length 5f, radius 2r Rank the wires according to their resistances, least to greatest.

Back 36

1 and 2 tie, then 5, 3, 4

Front 37

Of the following, the copper conductor that has the least resistance is:

Back 37

hick, short and cool

Front 38

A cylindrical copper rod has resistanceR. It is reformed to twice its original length with nochange of volume. Its new resistance is:

Back 38

4R

Front 39

The resistance of a rod does NOT depend on:

Back 39

he shape of its (fixed) cross-sectional area

Front 40

A certain wire has resistanceR. Another wire, of the same material, has half the length andhalf the diameter of thefirst wire. The resistance of the second wire is:

Back 40

2R

Front 41

A nichrome wire is 1 m long and 1×10−6m2in cross-sectional area. When connected to apotential difference of 2 V, a current of 4 A exists in the wire. The resistivity of this nichromeis:

Back 41

5×10−7Ω·m