Copper is the preferred material for lightning conductors because it is an excellent electrical conductor, allowing the massive current from a lightning strike to be safely diverted to the ground. Its high conductivity minimizes resistance, reducing the risk of heat buildup and damage to the structure. While aluminum is also used, copper is widely favored for its durability and superior performance in grounding systems.

An ideal voltmeter is designed to measure potential difference without drawing significant current from the circuit. Therefore, it must have infinite (or very high) resistance to ensure that the circuit's original current distribution remains undisturbed during the measurement process.

According to Ohm's Law, current (I) is calculated as Voltage (V) divided by Resistance (R). Using the values provided: I = 220V / 750 ohms. This calculation results in approximately 0.2933 A, which rounds to 0.29 A. This demonstrates the relationship between voltage, resistance, and current in a resistive load.

Resistivity is an intrinsic property of a material, determined by its atomic structure and temperature, rather than its physical dimensions. While cutting the wire changes its length and total resistance, the resistivity remains constant for the material. Therefore, dividing the wire into smaller segments does not alter the resistivity of the resulting pieces, as the material composition remains identical to the original wire.

For resistors connected in series, the total or resultant resistance (R_eq) is the sum of the individual resistances. Since there are three resistors of 25 Ω each, R_eq = 25 Ω + 25 Ω + 25 Ω = 75 Ω.

An ohmic conductor is defined by its adherence to Ohm's Law, which states that the current flowing through a conductor is directly proportional to the voltage applied across it, provided the temperature remains constant. This linear relationship results in a straight-line graph when plotting voltage versus current, where the slope represents the resistance of the material.

When resistors are connected in parallel, the reciprocal of the total resistance is equal to the sum of the reciprocals of the individual resistances. This configuration provides multiple paths for the current to flow, which effectively decreases the total equivalent resistance of the circuit compared to any single resistor in the network.

Ohm's Law states that the current flowing through a conductor is directly proportional to the potential difference across its ends, provided physical conditions like temperature remain constant. The ratio of voltage (V) to current (I) is defined as the resistance (R), which is constant for an ohmic conductor.

Resistivity values at 20°C are approximately: Iron (~1.0 x 10^-7 Ωm), Mercury (~9.6 x 10^-7 Ωm), Manganese (~1.44 x 10^-6 Ωm), and Chromium (~1.25 x 10^-7 Ωm). Manganese has the highest resistivity among these specific options.

Insulators are materials that do not allow the free flow of electric current because their electrons are tightly bound to their atoms. Consequently, they possess a very high electrical resistance, which prevents the movement of charge carriers through the material under normal conditions.