Question

If the ammeter reading is X ampere with nichrome wire of length $l$, then what will be the ammeter reading if the length of nichrome wire is doubled with same area of cross-section?

Answer 1

Concept: Resistance of a wire is directly proportional to its length. \[ R \propto l \] If length is doubled → Resistance doubles. From Ohm’s law, \[ I = \frac{V}{R} \] So current is inversely proportional to resistance. Result: If resistance doubles, current becomes half. \[ \text{New current} = \frac{X}{2} \]

Answer 2

Concept: Resistance is inversely proportional to area of cross-section. \[ R \propto \frac{1}{A} \] If area is doubled → Resistance becomes half. From Ohm’s law, \[ I = \frac{V}{R} \] So current increases when resistance decreases. Result: If resistance becomes half, current doubles. \[ \text{New current} = 2X \]

Answer 3

Definition: Resistivity is a property of a material that measures how strongly it opposes the flow of electric current. \[ \rho = \frac{RA}{l} \] SI Unit: Ohm metre ($\Omega$m) Comparison:

• Alloys generally have higher resistivity than their constituent pure metals.
• This is because impurities and irregular structure increase resistance to electron flow.

Answer 4

Tungsten has a very high melting point and can withstand high temperatures hookup without melting. It also has high resistivity and emits light when heated, making it ideal for lamp filaments. (ii) Conductors of bread-toasters are made of an alloy rather than a pure metal. Alloys have higher resistivity and do not oxidize easily at high temperatures. They can produce more heat and last longer than pure metals.

Answer 5

Tungsten has a very high melting point and can withstand high temperatures hookup without melting. It also has high resistivity and emits light when heated, making it ideal for lamp filaments. (ii) Conductors of bread-toasters are made of an alloy rather than a pure metal. Alloys have higher resistivity and do not oxidize easily at high temperatures. They can produce more heat and last longer than pure metals.