Question 1

Current has units:

Accepted Answer

A) kilowatt·hour 
B) coulomb/second 
C) coulomb 
D) volt 
E) ohm 
A) kilowatt·hour 
B) coulomb/second 
C) coulomb 
D) volt 
E) ohm

Question 2

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:

Accepted Answer

A) 0.056 W 
B) 0.167 W 
C) 0.50 W 
D) 1.5 W 
E) none of these 
A) 0.056 W 
B) 0.167 W 
C) 0.50 W 
D) 1.5 W 
E) none of these

Question 3

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

Accepted Answer

A) the current 
B) the length 
C) the cross-sectional area 
D) the resistivity 
E) the electron drift velocity 
A) the current 
B) the length 
C) the cross-sectional area 
D) the resistivity 
E) the electron drift velocity

Question 4

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:

Accepted Answer

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 
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

Question 5

An incandescent light bulb is marked "60 watt, 120 volt".Its resistance is:

Accepted Answer

A) 0.5 $\Omega$ 
B) 120 $\Omega$ 
C) 180 $\Omega$ 
D) 240$\Omega$ 
E) 300 $\Omega$ 
A) 0.5 $\Omega$ 
B) 120 $\Omega$ 
C) 180 $\Omega$ 
D) 240$\Omega$ 
E) 300 $\Omega$

Question 6

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 *7 A/m2.The current is:

Accepted Answer

A) 0.63 A 
B) 2.0 A 
C) 5.9 A 
D) 300 A 
E) 26000 A 
A) 0.63 A 
B) 2.0 A 
C) 5.9 A 
D) 300 A 
E) 26000 A

Question 7

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

Accepted Answer

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) 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

Question 8

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

Accepted Answer

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 
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

Question 9

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?

Accepted Answer

A) $1.20 
B) $1.50 
C) $1.80 
D) $7.20 
E) none of these 
A) $1.20 
B) $1.50 
C) $1.80 
D) $7.20 
E) none of these

Question 10

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:

Accepted Answer

A) R/4 
B) R/2 
C) R 
D) 2R 
E) 4R 
A) R/4 
B) R/2 
C) R 
D) 2R 
E) 4R

Question 11

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

Accepted Answer

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) 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

Question 12

In schematic diagrams, currents are indicated using arrows.What do the arrows indicate?

Accepted Answer

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 
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

Question 13

Five cylindrical wires are made of the same material.Their lengths and radii are   Rank the wires according to their resistances, least to greatest.

Accepted Answer

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) 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

Question 14

An iron is marked "120 volt, 600 watt".In normal use, the current in it is:

Accepted Answer

A) 0.2 A 
B) 2 A 
C) 4 A 
D) 5 A 
E) 7.2 A 
A) 0.2 A 
B) 2 A 
C) 4 A 
D) 5 A 
E) 7.2 A

Question 15

The resistance of a rod does NOT depend on:

Accepted Answer

A) its temperature 
B) its material 
C) its length 
D) its conductivity 
E) shape of its (fixed)cross-sectional area 
A) its temperature 
B) its material 
C) its length 
D) its conductivity 
E) shape of its (fixed)cross-sectional area

Question 16

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

Accepted Answer

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 
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

Question 17

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:

Accepted Answer

A) 0.83 A 
B) 2.0 A 
C) 3.5 A 
D) 500 A 
E) 2100 A 
A) 0.83 A 
B) 2.0 A 
C) 3.5 A 
D) 500 A 
E) 2100 A

Question 18

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

Accepted Answer

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 
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

Question 19

This figure shows a junction.What is true of the currents?

Accepted Answer

A) i1 = i0 + i2 
B) i2= i0 + i1 
C) i0 = i1 - i2 
D) i1 = i0 - i2 
E) i0 = i2- i1 
A) i1 = i0 + i2 
B) i2= i0 + i1 
C) i0 = i1 - i2 
D) i1 = i0 - i2 
E) i0 = i2- i1

Question 20

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:

Accepted Answer

A) 12 s 
B) 50 s 
C) 3.5 min 
D) 15 min 
E) 45 min 
A) 12 s 
B) 50 s 
C) 3.5 min 
D) 15 min 
E) 45 min

Exam 26: Current and Resistance

Current has units:

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:

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

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:

An incandescent light bulb is marked "60 watt, 120 volt".Its resistance is:

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 *7 A/m2.The current is:

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

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

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 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:

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

In schematic diagrams, currents are indicated using arrows.What do the arrows indicate?

Five cylindrical wires are made of the same material.Their lengths and radii are Rank the wires according to their resistances, least to greatest.

An iron is marked "120 volt, 600 watt".In normal use, the current in it is:

The resistance of a rod does NOT depend on:

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

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:

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

This figure shows a junction.What is true of the currents?

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:

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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 *⁷A/m².The current is:

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: