Current Electricity-2

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

• 3600 C

• 3000 C

• 2400 C

• 1800 C

Copper contains 8.4×1028 free electrons/ $m^3$  . A copper wire of cross-sectional area 7.4× $10^{-7}$  $m^2$  carries a current of 1 A. The electron drift speed is approximately: 

• 3×  $10^8$  m/s

•  $10^3$ m/s

• 1 m/s

•  $10^{-4}$  m/s

Five cylindrical wires are made of the same material. Their lengths and radii are:

wire 1: length f, radius r

wire 2: length f/4, radius r/2

wire 3: length f/2, radius r/2

wire 4: length f, radius r/2

wire 5: length 5f, radius 2r

Rank the wires according to their resistances, least to greatest.

• 1, 2, 3, 4, 5

• 5, 4, 3, 2, 1

• 1 and 2 tie, then 5, 3, 4

• 1, 3, 4, 2, 5

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

• thin, long and hot

• thick, short and cool

• thick, long and hot

• thin, short and cool

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:

• R/4

• R/2

• R

• 2R

A nichrome 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 nichrome

is:

• $10^{-7}$ Ω · m

• 2 × $10^{-7}$ Ω · m

• 4 × $10^{-7}$ Ω · m

• 5 × $10^{-7}$ Ω · m

Two conductors are made of the same material and have the same length. Conductor A is a
solid wire of diameter 1 m. Conductor B is a hollow tube of inside diameter 1 m and outside
diameter 2 m. The ratio of their resistance, , is: 

 $R_A$ / $R_B$  

• 1

•  $\sqrt{2}$  

• 3

• 2

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:

• 0.056 W

• 1.5 W

• 0.167 W

• 0.5 W

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

• 1.8 J

• 216 J

• 20 J

• 12 J

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

• 5600

• 26

• 87.5