Electricity Worksheet-17

Electricity Worksheet-17

 

  1. A wire of resistivity p is stretched to double its length. What is its new resistivity ?

 

  1. How many times (roughly) is the resistivity of an insulator greater than a metal ?

 

  1. What is the resistance of a connecting wire ?

 

  1. What is the resistance of an ammeter ?

 

  1. What is the resistance of a voltmeter?

 

  1. Which has more resistance : 100 W bulb or 60 W bulb ?

 

  1. Which material is the best conductor of electricity at room temperature ?

 

  1. What is the resistance of an air gap ?

 

  1. Why is resistance more in series combination of resistors ?

 

  1. Why is resistance less in parallel combination of resistors ?

 

Answer:

  1. There is no change in resistivity of the wire as it depends only on the material of the wire.

 

  1. 1025 times.

 

  1. The resistance of a connecting wire, which is made of a good conductor (copper), is negligible and is almost zero.

 

  1. The resistance of an ammeter is very small and for an ideal ammeter, its value is zero.

 

  1. The resistance of a voltmeter is very high and for an ideal voltmeter, its value is infinity.

 

  1. As P = V2/R, P ∝ 1/R or R ∝ 1/P. Thus, the resistance of 60 W bulb is more than that of 100 W bulb.

 

  1. Silver is the best conducting material at room temperature as its resistivity is the lowest of all the materials.

 

  1. Air is a very poor conductor of electricity as it has no charge carriers and its resistance is almost infinity.

 

  1. In series combination of resistors, the effective length of the conducting path increases and as such resistance increases as  R ∝ I.

 

  1. In parallel combination of resistors, the effective cross-sectional area of the resulting combination decreases and as such resistance decreases since  R ∝ 1/A.