# Electricity

### What is electrical resistivity? Derive its SI unit

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.

### What would be the readings of the ammeter and the voltmeter

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

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

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

Write Joule’s law of heating.

### Why are alloys commonly used in electrical heating devices

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

### Why are metals good conductors of electricity whereas glass is a bad conductor

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

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