The correct answer is A. Lorentz method.
The Lorentz method is a method for measuring the absolute resistance of a conductor. It is based on the principle that the magnetic field produced by a current flowing in a conductor is proportional to the current. The magnetic field is measured using a Hall probe, and the resistance is calculated from the measured field and the current.
The Raleigh method is a method for measuring the relative resistance of two conductors. It is based on the principle that the resistance of a conductor is proportional to its length and inversely proportional to its cross-sectional area. The resistance of the two conductors is measured using a Wheatstone bridge, and the relative resistance is calculated from the measured resistances.
Ohm’s law is a law that states that the current through a conductor is proportional to the voltage across it, provided that the temperature and other physical conditions remain constant. Ohm’s law cannot be used to measure the absolute resistance of a conductor, because it does not take into account the effects of temperature and other physical conditions.
The Wheatstone bridge is a circuit that is used to measure the resistance of an unknown resistor. The bridge is balanced when the voltage across the unknown resistor is equal to the voltage across a reference resistor. The resistance of the unknown resistor can then be calculated from the known resistance of the reference resistor and the other components in the bridge.
The Lorentz method is the most accurate method for measuring the absolute resistance of a conductor. It is also the most expensive and time-consuming method. The Raleigh method is less accurate than the Lorentz method, but it is less expensive and faster. Ohm’s law is not a reliable method for measuring the absolute resistance of a conductor. The Wheatstone bridge is a reliable method for measuring the relative resistance of two conductors, but it is not a reliable method for measuring the absolute resistance of a conductor.