What is electrical resistivity? Derive its SI unit. In a series electrical circuit comprising a resistor made up of a metallic wire, the ammeter reads 100 mA. If the length of the wire is doubled, how will the current in the circuit change? Justify your answer.


Consider the following circuit:


What would be the readings of the ammeter and the voltmeter when key is closed? Give reason to justify your answers.


Draw a circuit diagram of an electric circuit containing a cell, a key, an ammeter, a resistor of 4Ω in series with a combination of two resistors (8Ω each) in parallel and a voltmeter across parallel combination. Each of them dissipate maximum energy and can withstand a maximum power of 16W without melting. Find the maximum current that can flow through the three resistors.


Calculate the total cost of running the following electrical devices in the month of September, if the rate of 1 unit of electricity is Rs 6.00.

  1. Electric heater of 1000 W for 5 hours daily.
  2. Electric refrigerator of 400 W for 10 hours daily.

Write Joule’s law of heating.


Why are alloys commonly used in electrical heating devices? Give reason.


Why are metals good conductors of electricity whereas glass is a bad conductor of electricity? Give reason.


List the factors on which the resistance of a conductor in the shape of a wire depends.