EE Dreamforce Part 1

100問 • 1年前

問題一覧

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

Charge

Current has units of

coulomb/second

Current has units of:

ampere

The unit of resistivity are:

ohm-meter

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

watt

Energy may be measured in:

watt•second

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

Potential difference — J/C

Current is a measure of

amount of charge that moves past a point per unit time

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

the current density and electric field both point left

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

their cross-sectional areas are the same

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

2.0A

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

much less than the average electron speed

Two substances are identical except that the electron mean free time for substance A is twice the electron mean free time for substance B. If the same electric field exists in both substances the electron drift speed in A is:

twice that in B

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

for every electron with a given velocity there is another with a velocity of equal magnitude and opposite direction.

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

half that of electrons in B

If the potential difference across a resistor is doubled:

only the current is doubled.

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

thick short and cool

A cylindrical copper rod has resistance R. It is reformed to twice its original length with no change of volume. Its new resistance is:

The resistance of a rod does NOT depend on:

the shape of its (fixed) cross-sectional area

A certain wire has resistance h. Another wire, of the same material, has half the length and half the diameter of the first wire. The resistance of the second wire is:

Two wires are made of the same material and have the same length but different radii. They are joined end-to-end and a potential difference is maintained across the combination. Of the following the quantity that is the same for both wires is:

current

For an ohmic substance the resistivity is the proportionality constant for:

current density and electric field

For an ohmic resistor, resistance is the proportionality constant for:

current and potential difference

For an ohmic substance, the resistivity depends on:

the electron mean free time

For a cylindrical resistor made of ohmic material, the resistance does NOT depend on:

the currentt

For an ohmic substance, the electron drift velocity is proportional to:

the electric field in the sample

You wish to triple the rate of energy dissipation in a heating device. To do this you could triple:

the resistance keeping the current the same

A student kept her 60-watt, 120-volt study lamp turned on from 2:00 PM until 2:00 AM. How many coulombs of charge went through it?

21,600

A flat iron is marked "120 V, 600 W". In normal use, the current in it is:

An certain resistor dissipates 0.5 W when connected to a 3V potential difference. When connected to a 1 V potential difference, this resistor will dissipate:

0.056W

An ordinary light bulb is marked "60 W, 120 V". Its resistance is:

240 ohms

The mechanical equivalent of heat is 1 cal = 4.18 J. The specific heat of water is 1 cal/g K. An electric immersion water heater, rated at 400 W, should heat a kilogram of water from 10° C to 30° C in about:

3.5 min

It is better to send 10, 000 kW of electric power long distances at 10, 000 V rather than at 220 V because:

there is less heating in the transmission wire

Suppose the electric company charges 10 cents per kW.h. How much does it cost to use a 125 W lamp 4 hours a day for 30 days?

$1.50

A certain x-ray tube requires a current of 7 mA at a voltage of 80 kV. The rate of energy dissipation (in watts) is:

560

The mechanical equivalent of heat is 1 cal = 4.18 J. A heating coil, connected to a 120-V source, provides 60, 000 calories in 10 minutes. The current in the coil is:

3.5A

You buy a "75 W" light bulb. The label means that:

None of the above

A current of 0.3 A is passed through a lamp for 2 minutes using a 6-V power supply. The energy dissipated by this lamp during the 2 minutes is:

216J

"The sum of the currents into a junction equals the sum of the currents out of the junction" is a consequence of:

Conservation of acharge

"The sum of the emf's and potential differences around a closed loop equals zero" is a consequence of:

Conservation of energy

A portion of a circuit is shown, with the values of the currents given for some branches. What is the direction and value of the current i?

downward 6A

Four wires meet at a junction. The first carries 4A into the junction, the second carries 5 A out of the junction, and the third carries 2 A out of the junction. The fourth carries:

3A into the junction

In the context of the loop and junctions rules for electrical circuits a junction is:

where three or more wires are joined

For any circuit the number of independent equations containing emf's, resistances, and currents equals:

the number of branches

If a circuit has L closed loops, B branches, and J junctions the number of independent loop equations is:

B-J + 1

A battery is connected across a series combination of two identical resistors. If the potential difference across the terminals is V and the current in the battery is i, then:

the potential difference across each resistor is V/2 and the current in each resistor is i

A battery is connected across a parallel combination of two identical resistors. If the potential difference across the terminals is V and the current in the battery is i, then:

the potential difference across each resistor is V and the current in each resistor is i/2

A total resistance of 3.0 is to be produced by combining an unknown resistor R with a 1252 resistor. What is the value of R and how is it to be connected to the 1252 resistor?

4.0 ohms parallel

By using only two resistors, Ri and R2, a student is able to obtain resistances of 3 h, 45, 125, and 165. The values of Ri and R2 (in ohms) are:

4, 12

Four 20-0 resistors are connected in parallel and the combination is connected to a 20-V emf device. The current in the device is:

4.0 A

Four 20-52 resistors are connected in series and the combination is connected to a 20-V emf device. The current in any one of the resistors is:

0.25 A

Four 20-52 resistors are connected in series and the combination is connected to a 20-V emf device. The potential difference across any one of the resistors is:

Nine identical wires, each of diameter d and length L, are connected in parallel. The combination has the same resistance as a single similar wire of length L but whose diameter is:

Nine identical wires, each of diameter d and length L, are connected in series. The combination has the same resistance as a single similar wire of length L but whose diameter is:

d/3

Two wires made of the same material have the same lengths but different diameters. They are connected in parallel to a battery. The quantity that is NOT the same for the wires is:

the current

Two wires made of the same material have the same lengths but different diameters. They are connected in series to a battery. The quantity that is the same for the wires is:

the current

The resistance of resistor 1 is twice the resistance of resistor 2. The two are connected in parallel and a potential difference is maintained across the combination. Then:

the current in 1 is half that in 2

The resistance of resistor 1 is twice the resistance of resistor 2. The two are connected in series and a potential difference is maintained across the combination. Then:

the potential difference across 1 is twice that across 2

Resistor 1 has twice the resistance of resistor 2. The two are connected in series and a potential difference is maintained across the combination. The rate of thermal energy generation in 1 is:

twice that in 2

Resistor 1 has twice the resistance of resistor 2. The two are connected in parallel and a potential difference is maintained across the combination. The rate of thermal energy generation in 1 is:

half that in 2

The emf of a battery is equal to its terminal potential difference:

only when there is no current in battery

The terminal potential difference of a battery is less than its emf:

only when the battery is being discharged

A battery has an emf of 9 V and an internal resistance of 25. If the potential difference across its terminals is greater than 9V:

the current must be out of the negative terminal

A battery with an emf of 24 V is connected to a 6-5 resistor. As a result, current of 3 A exists in the resistor. The terminal potential difference of the battery is:

18V

Two identical batteries, each with an emf of 18 V and an internal resistance of 1S, are wired in parallel by connecting their positive terminals together and connecting their negative terminals together. The combination is then wired across a 4-52 resistor. The current in the 4-5 resistor is:

4.0A

2.0A

18V

A 120-V power line is protected by a 15-A fuse. What is the maximum number of "120 V, 500 W" light bulbs that can be operated at full brightness from this line?

Two 110-V light bulbs, one "25 W" and the other "100 W", are connected in series to a 110 V source. Then:

none of the above

A resistor with resistance Ri and a resistor with resistance R2 are connected in parallel to an ideal battery with emf E. The rate of thermal energy generation in the resistor with resistance Ri is:

E2/ R1

In an antique automobile, a 6-V battery supplies a total of 48 W to two identical headlights in parallel. The resistance (in ohms) of each bulb is:

1.5

Resistor 1 has twice the resistance of resistor 2. They are connected in parallel to a battery. The ratio of the thermal energy generation rate in 1 to that in 2 is:

1:2

A series circuit consists of a battery with internal resistance r and an external resistor R. If these two resistances are equal (r = R) then the thermal energy generated per unit time by the internal resistance r is:

the same as by R

The positive terminals of two batteries with emf's of E and Ez, respectively, are connected together. Here E2 > E1. The circuit is completed by connecting the negative terminals. If each battery has an internal resistance r, the rate with which electrical energy is converted to chemical energy in the smaller battery is:

E2 - E1) E1/2r

A certain galvanometer has a resistance of 100 and requires 1 mA for full scale deflection. To make this into a voltmeter reading 1 V full scale, connect a resistance of:

900 ohms in series

To make a galvanometer into an ammeter, connect:

a low resistance in parallel

A certain voltmeter has an internal resistance of 10, 000 and a range from 0 to 100V. To give it a range from 0 to 1000 V, one should connect:

90,000 ohms in series

A certain ammeter has an internal resistance of 1S and a range from 0 to 50 mA. To make its range from 0 to 5A, use:

a resistance of 1/99 ohms in parallel

A galvanometer has an internal resistance of 125 and requires 0.01 A for full scale deflection. To convert it to a voltmeter reading 3 V full scale, one must use a series resistance of:

288 ohms

A certain voltmeter has an internal resistance of 10,000 and a range from 0 to 12V. To extend its range to 120 V, use a series resistance of:

90,000 ohms

The time constant RC has unit of n

none of these

A charged capacitor is being discharged through a resistor. At the end of one time constant the charge has been reduced by (1 - 1/e) = 63% of its initial value. At the end of two time constants the charge has been reduced by what percent of its initial value?

86%

An initially uncharged capacitor C is connected in series with resistor R. This combination is then connected to a battery of emf Vo. Sufficient time elapses so that a steady state is reached. Which of the following statements is NOT true?

The total thermal energy generated by R is independent of R

A certain capacitor, in series with a resistor, is being charged. At the end of 10 ms its charge is half the final value. The time constant for the process is about:

14ms

A certain capacitor, in series with a 720-5 resistor, is being charged. At the end of 10 ms its charge is half the final value. The capacitance is about:

20ųf

In the capacitor discharge formula q = qoe-t/RC the symbol t represents:

none of the above

Units of a magnetic field might be:

kg/C•s

In the formula F = qu x B:

F must be perpendicular to both u and B

At any point the magnetic field lines are in the direction of:

none of the above

The magnetic force on a charged particle is in the direction of its velocity if:

Never

A magnetic field exerts a force on a charged particle:

if the particle is moving across the field lines

The direction of the magnetic field in a certain region of space is determined by firing a test charge into the region with its velocity in various directions in different trials. The field direction is:

one of the directions of the velocity when the magnetic force is zero

An electron is moving north in a region where the magnetic field is south. The magnetic force exerted on the electron is:

zero

A magnetic field CANNOT:

change the kinetic energy of a charged particle

A hydrogen atom that has lost its electron is moving east in a region where the magnetic field is directed from south to north. It will be deflected:

A beam of electrons is sent horizontally down the axis of a tube to strike a fluorescent screen at the end of the tube. On the way, the electrons encounter a magnetic field directed vertically downward. The spot on the screen will therefore be deflected:

to the right as seen from the electron source

An electron (charge = -1.6 x 10-19 C) is moving at 3 x 105 m/s in the positive x direction. A magnetic field of 0.8 T is in the positive z direction. The magnetic force on the electron is:

4 × 10-14N, in the positive y direction

At one instant an electron (charge = -1.6 × 10-19 C) is moving in the xy plane, the components of its velocity being Ux = 5 x 105 m/s and vy = 3 x 105m/s. A magnetic field of 0.8 T is in the positive x direction. At that instant the magnitude of the magnetic force on the electron is:

3.8 × 10-14 N

At one instant an electron (charge = -1.6 x 10-19 C) is moving in the ay plane, the components of its velocity being v, = 5 x 10° m/s and vy = 3 x 109 m/s. A magnetic field of 0,8 T is in the positive & direction. At that instant the magnitude of the magnetic force on the electron is:

3.8x10-14N

100

An electron travels due north through a vacuum in a region of uniform magnetic field B that is also directed due north. It will:

be unaffacted by the field

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ユーザ名非公開 · 41問 · 13日前

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