Electricity Test - 14

The resistance of a uniform metallic conductor is directly proportional to its length (l) and inversely proportional to the area of its cross-section (a). R=ρl/a where ρ is a constant of proportionality and is called the electrical resistivity of the material of the conductor. Resistivity of a conductor is a characteristic property of the material. If the length of the conductor is doubled and the area is halved, the resistivity will remain the same i.e. 2 × 10⁻³Ωm

Electrical resistivity (also known as resistivity) is an intrinsic property of a material that quantifies how strongly a given material opposes the flow of electric current. A low resistivity of a material indicates that the material readily allows the flow of electric current. Both the resistance and resistivity of a material vary with temperature. Resistivity of a conductor increases with increase in temperature. Resistivity of semiconductors decreases with increase in temperature.

The two wires are of the same length and the same radius; hence, their resistance will be proportional to their resistivity. Nichrome wire is an alloy of nickel, chromium, manganese and iron and has a resistivity of 100 x 10^-6 ohm-m. Copper has a low resistivity of 1.62 x 10^-8 ohm-m. Therefore, the Nichrome wire will get heated first. According to Joule's law of heating, the heat produced in a resistor is directly proportional to the resistance for a given current. H = I²Rt. Also, Nichrome does not oxidise easily at high temperatures. That is why, it is commonly used in electrical heating devices like electrical iron, heaters, etc.

Power (P) is the rate at which electric energy is lost (dissipated) or consumed in an electrical device due to resistance (R). P=V²/R

The rate of heat produced by the heater will remain the same since 'V' remains the same, and the resistance 'R' of the heater remains the same.

Tungsten is exclusively used for making filaments of electric bulbs. Nichrome is an alloy of nickel, chromium, manganese and iron and does not oxidise easily at high temperatures. It is commonly used in electrical heating devices like electrical iron, heaters, etc. Superconductors are materials that conduct electricity with zero resistivity. EMF (Electro Motive Force) of a battery creates a potential difference across a circuit.

Silver is the best conductor. It has a resistivity of 1.6 x 10^-8 ohm-m. Ebonite is a very hard rubber obtained by vulcanizing natural rubber for prolonged periods. It has a resistivity in the range of 10¹⁵ to 10¹⁷ ohm-m and acts as an insulator. Silicon is a semi-conductor. Constantan is an alloy of copper and nickel and is used to make standard resistors. It has a resistivity of 49 x 10^-6 ohm-m.

The SI unit of electric current is ampere (symbol A). It is named after the French scientist - Andre Marie Ampere. The ohm (symbol Ω) is the SI unit of electrical resistance, named after German physicist - Georg Simon Ohm. The SI unit of potential difference is volt (symbol V), named after the Italian physicist - Alessandro Volta. The SI unit of resistivity is ohm-metre (symbol Ω-m).