Quiz 26: Current and Resistance

A car battery is rated at 80 Ah.An ampere-hour is a unit of: A)power B)energy C)current D)charge E)force

Current has units: A)kilowatt·hour B)coulomb/second C)coulomb D)volt E)ohm

Current has units: A)kilowatt·hour B)ampere C)coulomb D)volt E)ohm

Current is a measure of: A)force that moves a charge past a point B)resistance to the movement of a charge past a point C)energy used to move a charge past a point D)amount of charge that moves past a point per unit time E)speed with which a charge moves past a point

A 60-watt light bulb carries a current of 0.5 ampere.The total charge passing through it in one hour is: A)3600 C B)3000 C C)2400 C D)1800 C E)120 C

A 10-ohm resistor has a constant current.If 1200 C of charge flow through it in 4 minutes what is the value of the current? A)3.0 A B)5.0 A C)20 A D)120 A E)300 A

Current in a conductor is normally due to: A)the collective motion of all electrons in the conductor B)the thermal motion of the conduction electrons C)the drift motion of the conduction electrons due to electric fields D)the drift motion of both electrons and positrons E)the drift motion of both electrons and protons

This figure shows a junction.What is true of the currents? A)i₁ = i₀ + i₂ B)i₂= i₀ + i₁ C)i₀ = i₁ - i₂ D)i₁ = i₀ - i₂ E)i₀ = i₂- i₁

In schematic diagrams, currents are indicated using arrows.What do the arrows indicate? A)the direction of motion of the electrons B)the direction of the current vector C)the direction of motion of the charge carriers D)the direction that positive charge carriers would move E)nothing; they are just a convenient drawing tool

Conduction electrons move to the right in a certain wire.This indicates that: A)the current density and electric field both point right B)the current density and electric field both point left C)the current density points right and the electric field points left D)the current density points left and the electric field points right E)the current density points left but the direction of the electric field is unknown

If is the current density and is a vector element of area then the integral over an area represents: A)the electric flux through the area B)the average current density at the position of the area C)the resistance of the area D)the resistivity of the area E)the current through the area

Two wires made of different materials have the same uniform current density.They carry the same current only if: A)their lengths are the same B)their cross-sectional areas are the same C)both their lengths and cross-sectional areas are the same D)the potential differences across them are the same E)the electric fields in them are the same

A wire with a length of 150 m and a radius of 0.15 mm carries a current with a uniform current density of 2.8 10⁷ A/m².The current is: A)0.63 A B)2.0 A C)5.9 A D)300 A E)26000 A

In a conductor carrying a current we expect the electron drift speed to be: A)much greater than the average electron speed B)much less than the average electron speed C)about the same as the average electron speed D)less than the electron speed at low temperature and greater than the electron speed at high temperature E)less than the electron speed at high temperature and greater than the electron speed at low temperature

The current is zero in a conductor when no potential difference is applied because: A)the electrons are not moving B)the electrons are not moving fast enough C)for every electron with a given velocity there is another with a velocity of equal magnitude and opposite direction D)equal numbers of electrons and protons are moving together E)otherwise Ohm's law would not be valid

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: A)twice that of electrons in B B)four times that of electrons in B C)half that of electrons in B D)one-fourth that of electrons in B E)the same as that of electrons in B

Copper contains 8.4  10²⁸ free electrons per cubic meter.A copper wire of cross-sectional area 7.4  10^-7 m² carries a current of 1 A.The electron drift speed is approximately: A)3  10⁸ m/s B)10³ m/s C)1 m/s D)10^-4 m/s E)10^-23 m/s

The units of resistivity are: A)ohm B)ohm·meter C)ohm/meter D)ohm/meter² E)none of these

If the potential difference across a resistor is doubled: A)only the current is doubled B)only the current is halved C)only the resistance is doubled D)only the resistance is halved E)both the current and resistance are doubled

A current of 0.5 ampere exists in a 60-ohm lamp.The applied potential difference is: A)15 V B)30 V C)60 V D)120 V E)none of these

A wire has an electric field of 6.2 V/m and carries a current density of 2.4 x 10⁸ A/m².What is its resistivity? A)6.7 x 10^-10 m B)1.5 x 10^-8 m C)2.6 x 10^-8 m D)3.9 x 10⁷ m E)1.5 x 10⁹ m

Conductivity is: A)the same as resistivity, it is just more convenient to use for good conductors B)expressed in ^-1 C)equal to 1/resistance D)expressed in (m)^-1 E)not a meaningful quantity for an insulator

Five cylindrical wires are made of the same material.Their lengths and radii are Rank the wires according to their resistances, least to greatest. A)1, 2, 3, 4, 5 B)5, 4, 3, 2, 1 C)1 and 2 tie, then 5, 3, 4 D)1, 3, 4, 2, 5 E)1, 2, 4, 3, 5

A cylindrical copper rod has resistance R.It is reformed to twice its original length with no change of volume.Its new resistance is: A)R/2 B)R C)2R D)4R E)8R

A certain wire has resistance R.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: A)R/4 B)R/2 C)R D)2R E)4R

A wire is 1 m long and 1  10^-6 m² in cross-sectional area.When connected to a potential difference of 2 V, a current of 4 A exists in the wire.The resistivity of this wire is: A)2  10^-6 m B)8  10^-6 m C)1  10^-7 m D)4  10^-7 m E)5  10^-7 m

Of the following the copper conductor that has the least resistance is: A)thin, long and hot B)thick, short and cool C)thick, long and hot D)thin, short and cool E)thin, short and hot

The resistance of a rod does NOT depend on: A)its temperature B)its material C)its length D)its conductivity E)shape of its (fixed)cross-sectional area

Which of the following graphs best represents the current-voltage relationship of an incandescent light bulb? A)I B)II C)III D)IV E)V

Which of the following graphs best represents the current-voltage relationship for a device that obeys Ohm's law? A)I B)II C)III D)IV E)V

A certain sample carries a current of 4 A when the potential difference is 2 V and a current of 10 A when the potential difference is 4 V.This sample: A)obeys Ohm's law B)has a resistance of 0.5  at 2 V C)has a resistance of 2  at 2 V D)has a resistance of 25  at 2 V E)does not have a resistance

For an ohmic resistor, resistance is the proportionality constant for: A)potential difference and electric field B)current density and electric field C)current and length D)current and cross-sectional area E)current and potential difference

For a cylindrical resistor made of ohmic material, the resistance does NOT depend on: A)the current B)the length C)the cross-sectional area D)the resistivity E)the electron drift velocity

For an ohmic substance the resistivity is the proportionality constant for: A)current and potential difference B)current and electric field C)current density and potential difference D)current density and electric field E)potential difference and electric field

For an ohmic substance, the electron drift velocity is proportional to: A)the cross-sectional area of the sample B)the length of the sample C)the mass of an electron D)the electric field in the sample E)none of the above

For an ohmic substance, the resistivity depends on: A)the electric field B)the potential difference C)the current density D)the electron mean free time E)the cross-sectional area of the sample

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: A)the same as in B B)twice that in B C)half that in B D)four times that in B E)one fourth that in B

The rate at which electrical energy is used may be measured in: A)watt/second B)watt·second C)watt D)joule·second E)kilowatt·hour

Energy may be measured in: A)kilowatt B)joule·second C)watt D)watt·second E)volt/ohm

Suppose the electric company charges 10 cents per kWh.How much does it cost to use a 125 watt lamp 4 hours a day for 30 days? A)$1.20 B)$1.50 C)$1.80 D)$7.20 E)none of these

The mechanical equivalent of heat is 1 cal = 4.18 J.A heating coil, connected to a 120-V source, develops 60,000 calories in 10 minutes.The current in the coil is: A)0.83 A B)2.0 A C)3.5 A D)500 A E)2100 A

Which one of the following quantities is correctly matched to its unit? A)power - kW·h B)energy - kW C)potential difference - J/C D)current - A/s E)resistance - V/C

You wish to triple the rate of energy dissipation in a heating device.To do this you could triple: A)the potential difference keeping the resistance the same B)the current keeping the resistance the same C)the resistance keeping the potential difference the same D)the resistance keeping the current the same E)both the potential difference and current

A student kept her 60-watt, 120-volt study lamp turned on from 2:00 PM until 2:00 AM.How much charge went through it? A)720 C B)3,600 C C)7,200 C D)18,000 C E)21,600 C

An iron is marked "120 volt, 600 watt".In normal use, the current in it is: A)0.2 A B)2 A C)4 A D)5 A E)7.2 A

A certain resistor dissipates 0.5 W when connected to a 3 V potential difference.When connected to a 1 V potential difference, this resistor will dissipate: A)0.056 W B)0.167 W C)0.50 W D)1.5 W E)none of these

An incandescent light bulb is marked "60 watt, 120 volt".Its resistance is: A)0.5  B)120  C)180  D)240  E)300 

The mechanical equivalent of heat is 1 cal = 4.18 J.The specific heat of water is 1 cal/g·K, and its mass is 1 g/cm³.An electric immersion water heater, rated at 400 W, should heat a liter of water from 10C to 30C in about: A)12 s B)50 s C)3.5 min D)15 min E)45 min

It is better to send 10,000 kW of electric power long distances at 10,000 V rather than at 220 V because: A)there is less heating in the transmission wires B)the resistance of the wires is less at high voltages C)more current is transmitted at high voltages D)the insulation is more effective at high voltages E)the iR drop along the wires is greater at high voltage

A certain x-ray tube requires a current of 7 mA at a voltage of 80 kV.The rate of energy dissipation is: A)5600 W B)560 W C)26 W D)11.4 W E)0.088 W

You buy a "75 W" light bulb.The label means that: A)no matter how you use the bulb, the power will be 75 W B)the bulb was filled with 75 W at the factory C)the actual power dissipated will be much higher than 75 W since most of the power appears as heat D)the bulb is expected to "burn out" after you use up its 75 watts E)none of the above

A current of 0.3 A passes through a lamp for 2 minutes using a 6 V power supply.The energy dissipated by this lamp during the 2 minutes is: A)1.8 J B)12 J C)20 J D)36 J E)216 J

A 1.5-V battery is connected to a circuit and puts out a current of 0.45 A.How much power is the battery putting out? A)0.30 W B)0.68 W C)3.3 W D)5.0 W E)7.4 W

Compared to a conductor, a semiconductor A)has larger conductivity B)has smaller resistivity C)has a larger charge carrier density D)has a negative temperature coefficient of resistivity E)has zero resistivity