Electricity Worksheet-2

Electricity Worksheet-2

 

  1. The resistance of a straight conductor is independent of:

A. temperature                             B. material

C. cross-sectional area                D. shape of cross-section.

 

  1. The resistivity of a wire :

A. varies with its length

B. varies with its cross-section

C. varies with its mass

D. is independent of length, cross-section and mass of the wire.

 

  1. Two resistances R1 and R2 are connected in parallel. Their equivalent resistance is :

A. R1 + R2                                     B.

C.                                     D.

 

  1. If a wire of resistance R is melted and recast to half its length, the new resistance of the wire will be:

A. R/4                B. R/2                C. R                     D. 2 R.

 

  1. Three resistances of 2Ω, 4Ω and 8Ω are connected in parallel. Their equivalent resistance is :

A. 14 Ω                                            B. 10 Ω

C. (8/7) Ω                                      D. between 2 Ω and 8 Ω

 

  1. If n equal resistances are first connected in series and then connected in parallel, the ratio of the maximum to the minimum resistance is :

A. n                     B. 1/n2                C. n2                    D. 1/n

 

  1. If R1 and R2 are the resistances of filaments of a 400 W and a 200 W lamp, designed to operate on the same voltage, then :

A. R1 = 2R2        B. R2 = 2R1        C. R2 = 4R1        D. R1 = R2

 

  1. An electric bulb is rated 220 V – 100 W.  If it is operated at 110 V, then power consumed by it will be :

A. 100 W            B. 50 W              C. 25 W              D. 400 W

 

  1. A current of 2 A  passes through a conductor and produces 80 J of heat in 10 second. The resistance of the conductor is :

A. 0.5 Ω              B. 2 Ω                 C. 4 Ω                 D. 0.20 Ω

 

  1. A house has 10 tubes each of 40 W. If all the tubes are lighted for 10 hours and if the cost of one unit of electric energy is Rs. 2.50, the total cost of electricity consumption is :

A. Rs. 100          B. Rs. 20            C. Rs. 25            D. Rs. 10.

 

Answer Key:

  1. D
  2. D
  3. B
  4. A

Explanation: Volume of the wire will not change when the wire is melted and recast. If l and A are the original length and area of cross-section and l’ and A’ are their corresponding values on recasting,

                   Al = A' l'   or     

Since        

R’ (new resistance) =  P l’/ A’

         

Or     R’ = R/4.

  1. C

Explanation: 1/2 +1/4 + 1/8 = (8/7) Ω

  1. C
  2. B

Explanation: For the same voltage (V), 

and (as P = V2/R)

Thus,           or      R2 = 2R1

  1. C

Explanation: Assuming that with the change in temperature, there is no variation in the resistance of bulb,

     or     

or     

  1. B
  2. Explanation: As H = I2 Rt, 

D

Explanation: Electric energy consumed = 10 × (40W × 10h) = 4000 Wh = 4 kWh

Cost of electricity consumption Rs. 4 × 2.50 = Rs. 10