English
Menu

Circuit and electromagnetism basics

In a voltage divider made of two 10 kΩ resistors in series across a 10 V DC supply, a 10 kΩ load resistor is connected in parallel with the lower (ground-side) resistor. Which is closest to the output voltage (across the lower resistor)?

  1. A5 V
  2. BAbout 3.3 V
  3. CAbout 6.7 V
Show answer and explanation

Answer: B. About 3.3 V

With the load connected, the lower resistor and the load are in parallel, giving 10 × 10/(10 + 10) = 5 kΩ. The output is 10 V × 5/(10 + 5) ≈ 3.33 V, a large drop from the 5 V with no load. Treating the output as a Thevenin equivalent (5 V, 5 kΩ) driving 10 kΩ gives the same result: 5 V × 10/(5 + 10) ≈ 3.33 V. To reduce loading, make the divider resistors much smaller than the load or buffer the output (voltage follower).

  • A. 5 V is the voltage with no load connected.
  • B. Correct. 10 V × 5 kΩ/(10 kΩ + 5 kΩ) ≈ 3.33 V.
  • C. About 6.7 V is the result if the load were placed across the upper resistor.
Practice this topic Back to topic

Related calculators

Series and Parallel CalculatorSeries and parallel totals of resistors, capacitors or inductors, and pairs of E24 values that make a targetResistor Color Code CalculatorRead resistance and tolerance from color bands, or find the bands for a value

Books on Circuit and electromagnetism basics Ad

As an Amazon Associate I earn from qualifying purchases.

More Circuit and electromagnetism basics questions

  1. For a balanced three-phase load with a line voltage of 200 V, a line current of 10 A and a power factor of 0.8, which is closest to the load's active power (total of all three phases)?
  2. Which is closest to the bandwidth (the difference between the two frequencies at which the current falls to 1/√2 of its resonant value) of a series RLC resonant circuit with R = 10 Ω, L = 1 mH and C = 10 nF?
  3. A DC voltage is applied through a resistor R = 10 kΩ to an uncharged capacitor C = 10 µF. Which is closest to the time for the capacitor voltage to reach 50% of its final value?
  4. An uncharged capacitor C is fully charged from a DC voltage E through a resistor R. Which correctly gives the energy dissipated in the resistor during charging?
  5. A coil and a 10 Ω resistor are connected in series to a 10 V DC source, and a 100 Ω resistor is connected in parallel with the coil. After a long time, a switch disconnects the source and the 10 Ω resistor. What is the magnitude of the voltage across the 100 Ω resistor immediately after disconnection? (Ignore the coil's winding resistance.)