Deck 10: Current and Resistance

Question 1

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

A) 120 C
B) 3600 C
C) 3000 C
D) 2400 C
E) 1800 C

Answer 1

1800 C

Question 2

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

Answer 2

the current through the area

Question 3

Five cylindrical wires are made of the same material.Their lengths and radii are
Wire 1: length radius r
Wire 2: lenth radius r/2
Wire 3: length radius r/2
Wire 4: length radius r/2
Wire 5: length radius r/2
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

Answer 3

1 and 2 tie, then 5, 3, 4

Question 4

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

Question 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
B) 2R
C) 4R
D) 8R
E) R/2

Question 6

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

Question 7

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

Question 8

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

Question 9

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

Question 10

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

A) potential difference and electric field
B) current and electric field
C) current and length
D) current and cross-sectional area
E) current and potential difference

Question 11

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-sectionalarea of the sample

Question 12

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

Question 13

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

Question 14

An 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) 0.5 W
B) 0.167 W
C) 1.5 W
D) 0.056 W
E) none of these

Question 15

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:

A) 560
B) 5600
C) 26
D) 11.4
E) 87.5

Question 16

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:

A) 1.8 J
B) 12 J
C) 20 J
D) 36 J
E) 216 J