Chapter 1 · Principles of Electricity

1.9Review Questions

  1. Define current, voltage and resistance, with units.
  2. A current of 0.2 A flows for 30 s. How much charge passes?
  3. Find the current through a 330 Ω resistor connected to 5 V.
  4. Calculate the resistor needed for a red LED (1.8 V, 15 mA) on a 5 V supply.
  5. Find the equivalent resistance of 1 kΩ, 2 kΩ and 3 kΩ in series.
  6. Find the equivalent resistance of two 1 kΩ resistors in parallel.
  7. A 60 W bulb runs for 5 hours. How many kWh does it use?
  8. Why must a multimeter be placed in series to measure current?
Show answers
  1. Q = I × t = 0.2 × 30 = 6 C.
  2. I = 5 / 330 = 15.2 mA.
  3. R = (5 − 1.8) / 0.015 = 213 Ω, so use 220 Ω.
  4. 6 kΩ.
  5. 500 Ω.
  6. 60 W × 5 h = 300 Wh = 0.3 kWh.
  7. Current is the same everywhere in a series path. The meter must be part of the path so the whole current flows through it. Meters measure current by passing it through a very low resistance.