Concepts to remember for Wheatstone’s bridge:

• Principle of Wheatstone’s bridge: Wheatstone’s bridge is a network of four resistors connected in a diamond shape. When the ratio of two adjacent resistances is equal to the ratio of the other two adjacent resistances, the bridge is said to be balanced and no current flows through the galvanometer connected between the two diagonally opposite points.

• Balancing condition for Wheatstone’s bridge: In the Wheatstone’s bridge, the potential difference between the two diagonally opposite points is zero when the ratio of the first and second resistors is equal to the ratio of the third and fourth resistors: $$ \frac{R_1}{R_2} = \frac{R_3}{R_4} $$

• Applications of Wheatstone’s bridge:

  • Measurement of unknown resistance
  • Strain measurement
  • Temperature measurement
  • Measurement of capacitance

Concepts to remember for meter bridge:

• Principle of meter bridge: Meter bridge is a uniform wire of known resistance stretched between two thick copper strips. A jockey is used to make contact with the wire at any point. When the jockey is at the null point (balance point), the ratio of the lengths of the wire on either side of the jockey is equal to the ratio of the resistances connected to the corresponding ends of the wire.

• Balancing condition for meter bridge: Balancing condition for the meter bridge is given by: $$ \frac{P}{Q} = \frac{R}{S}$$ Where P and Q are the resistances on the left gap, R is an unknown resistance, and S is the resistance on the right gap.

• Applications of meter bridge:

• Measurement of unknown resistance

• Comparison of resistances

• Determination of specific resistance

Concepts to remember for potentiometer:

• Principle of potentiometer: Potentiometer is a device used to compare the emf of two cells. It consists of a long wire of uniform cross-sectional area and a jockey. When the jockey is moved along the wire, the potential difference between the jockey and one end of the wire changes. This potential difference is balanced against the emf of the two cells.

• Comparison of emf of two cells using a potentiometer: To compare the emf of two cells using a potentiometer, the cells are connected in opposition to each other across the potentiometer wire. The jockey is moved along the wire until the galvanometer connected between the jockey and the middle point of the battery shows no deflection. At this point, the potential difference across the potentiometer wire is equal to the emf of the cells.

• Internal resistance of a cell using a potentiometer: The internal resistance of a cell can be determined using a potentiometer. The cell is connected in series with a variable resistor and a potentiometer. The jockey is moved along the wire until the galvanometer shows no deflection. At this point, the potential difference across the potentiometer wire is equal to the emf of the cell. The internal resistance of the cell is calculated using Ohm’s law.

• Determination of the thermo emf of a thermocouple: Thermocouple is a device used to measure temperature. It consists of two different metals joined at their ends. When the two ends of the thermocouple are at different temperatures, an emf is generated. This emf is known as thermo emf. The thermo emf of a thermocouple can be determined using a potentiometer.

• Applications of potentiometer:

  • Measurement of emf
  • Measurement of internal resistance
  • Calibration of voltmeter
  • Calibration of ammeter
  • Temperature measurement