Analog and electronic circuits

In a Wheatstone bridge made of four resistors R1, R2, R3 and R4 (R1 and R2 in series, R3 and R4 in series, with the two pairs in parallel), what is the condition for no current to flow between the midpoints of the two pairs (balance)?

  1. AR1 + R2 = R3 + R4
  2. BR1 / R2 = R3 / R4
  3. CR1 × R2 = R3 × R4
Show answer and explanation

Answer: B. R1 / R2 = R3 / R4

If the voltages at the midpoints of the two series pairs are equal, no current flows between them. Each midpoint voltage is set by its divider ratio, so the balance condition is R1/R2 = R3/R4 (R1 × R4 = R2 × R3). The circuit is used to measure tiny resistance changes, such as in strain gauges, with high sensitivity.

  • A. Equal sums do not balance the bridge unless the divider ratios are equal.
  • B. Correct. Balance requires equal divider ratios on both sides.
  • C. The correct product form is R1 × R4 = R2 × R3, not R1 × R2 = R3 × R4.
Practice this topic Back to topic

More Analog and electronic circuits questions

  1. Which correctly states Thevenin's theorem?
  2. What does a high Q (quality factor) of a resonant circuit mean?
  3. What is the output impedance of an ideal current source?
  4. Why are crystal oscillators widely used as clock sources for watches and microcontrollers?
  5. What does the dropout voltage of an LDO (low-dropout linear regulator) mean?