Explanation: A Wheatstone bridge is used for the measurement of medium resistance in the range of 1ῼ to a few megaohms. Kelvin bridge is used for the measurement of low resistance.

Explanation: The main source of error in a Wheatstone bridge is because of the limiting errors of the three known resistances. As a result very precise resistances are required with 1 % tolerance.

Explanation: Resistance of contact wires and power dissipation are some of the causes for error in a null detector. But insufficient sensitivity is the major source of error in a null detector such as a galvanometer.

Explanation: Current flow through the resistances causes power dissipation i.e. I2R leading to an increase in the temperature. As the bridge consists of pure resistances, there is no back e.m.f induced.

Explanation: Temperature affects resistance of the circuit. Resistance has a positive temperature coefficient and increases linearly with rise in temperature.

Explanation: Heating effect can be eliminated by limiting the current through the circuit to a safe value and by calculating the power dissipation in the arms. Heat sinks are typically used in power electronic applications.

Explanation: Voltage drop across the circuit along with power dissipation lead to errors in the measurement of low resistances. The resistance of leads and contacts of the external circuit adds to the values in the circuit. This is the main source of error while measuring low resistances.

Explanation: When dissimilar metals come into contact with each other in a galvanometer circuit, thermal emf is generated. Null detector is used for detecting the balance condition.

Explanation: Thermal emf can be eliminated by making use of sensitive galvanometers consisting of copper coils and copper suspension systems. Dissimilar metals can’t be physically separated.