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Electronics Worksheet: Components and Ohm’s Law Test

Electronics lesson 20: Part 2 test: components and Ohm’s law · Set 844 · 40 questions
TalentJR

Remember (Find the topic, use the formula): Find the topic and the formula: V = I × R, I = V ÷ R, R = V ÷ I, P = V × I, units = W × h ÷ 1000. Change mA to A and kΩ to Ω before using a formula. Check: put your answer back into the formula.

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  1. 1.🧾 A 100 W filament bulb is swapped for a 15 W LED lamp that gives about the same light. Both would run for 5 hours. How many watt-hours (Wh) are saved?
  2. 2.True or false: to use daylight to read wastes electricity. (a) False (b) True
  3. 3.⚡ Which formula gives electric power? (a) P = V ÷ I (b) P = V × I (c) P = I ÷ V (d) P = V + I
  4. 4.🔺 A current of 25 mA flows through a 470 Ω resistor. What is the voltage across it (in volts)? =
  5. 5.⚡ A home appliance on the 230 V mains takes 4 A. What is its power (in watts)?
  6. 6.🔺 An 8 V supply is joined across a 200 Ω resistor. What current flows (in milliamperes, mA)?
  7. 7.🔺 A 2 V supply is joined across a 10 Ω resistor. What current flows (in amperes)? =
  8. 8.True or false: the voltmeter measures current. (a) False (b) True
  9. 9.⚡ A device works on 12 V and takes 0.2 A. What is its power (in watts)? =
  10. 10.🔍 Which is the odd one out? (a) close the fridge quickly (b) set the AC to 24 °C (c) run fans in empty rooms (d) switch off empty rooms
  11. 11.📏 How many kilo-ohms (kΩ) is 2700 Ω? =
  12. 12.🔺 A current of 50 mA flows through a 500 Ω resistor. What is the voltage across it (in volts)? =
  13. 13.⚡ A device works on 5 V and takes 0.1 A. What is its power (in watts)? =
  14. 14.True or false: a buzzer beeps for an alarm. (a) False (b) True
  15. 15.🧾 Which lamp gives the same light for the least power? (a) a candle (b) an oil lamp (c) a filament bulb (d) an LED lamp
  16. 16.🧩 A capacitor in a circuit can … (a) make light (b) measure heat (c) store charge briefly (d) spin a wheel
  17. 17.📏 How many watts (W) is 2 kW?
  18. 18.💡 A red LED uses 2 V and should get 20 mA. It runs from a 9 V supply. What resistor (in ohms) is needed in series?
  19. 19.🌈 Which band is read first on a resistor? (a) the gold band (b) the one nearest an end (c) the widest gap (d) any band
  20. 20.True or false: a capacitor smooths a wobbly supply. (a) False (b) True
  21. 21.True or false: a diode limits the current. (a) True (b) False
  22. 22.🌈 Which colour bands (1st digit, 2nd digit, multiplier) mark a 510 Ω resistor? (a) green-brown-red (b) brown-green-brown (c) green-brown-brown (d) green-brown-black
  23. 23.⚡ A home appliance on the 230 V mains takes 1.5 A. What is its power (in watts)?
  24. 24.🌈 A resistor has the colour bands white, red, brown. What is its value (in ohms)?
  25. 25.💡 Does it save or waste electricity to close the fridge quickly? (a) saves electricity (b) wastes electricity
  26. 26.True or false: to leave fridge door open wastes electricity. (a) False (b) True
  27. 27.🌈 A gold fourth band on a resistor means the value may be off by … (a) 0 % (b) 5 % (c) 50 % (d) 25 %
  28. 28.🔺 A current of 0.5 A flows through a 15 Ω resistor. What is the voltage across it (in volts)? =
  29. 29.💡 A red LED (it uses 2 V) is joined with a 200 Ω resistor to a 4 V supply. What current flows (in mA)?
  30. 30.⚡ A device works on 5 V and takes 1 A. What is its power (in watts)? =
  31. 31.⚡ A 1.25 W device works on 5 V. What current does it take (in amperes)? =
  32. 32.💡 A red LED (it uses 2 V) is joined with a 100 Ω resistor to a 4 V supply. What current flows (in mA)?
  33. 33.🌈 In the resistor colour code, which number does violet stand for?
  34. 34.💡 A blue LED uses 3 V and should get 10 mA. It runs from a 9 V supply. What resistor (in ohms) is needed in series?
  35. 35.🔺 The voltage stays the same and the resistance gets bigger. The current … (a) becomes zero (b) stays the same (c) gets smaller (d) gets bigger
  36. 36.📏 Which unit measures voltage? (a) ampere (A) (b) volt (V) (c) watt (W) (d) ohm (Ω)
  37. 37.🧮 Two resistors in parallel give a total that is … (a) more than either one (b) less than either one (c) always zero (d) their sum
  38. 38.🔺 A current of 1 A flows through a 6 Ω resistor. What is the voltage across it (in volts)? =
  39. 39.⚡ A 3 W device works on 12 V. What current does it take (in amperes)? =
  40. 40.⚡ A device works on 12 V and takes 0.1 A. What is its power (in watts)? =

Answer key

  1. 425
  2. False
  3. P = V × I
  4. 11.75
  5. 920
  6. 40
  7. 0.2
  8. False
  9. 2.4
  10. run fans in empty rooms
  11. 2.7
  12. 25
  13. 0.5
  14. True
  15. an LED lamp
  16. store charge briefly
  17. 2000
  18. 350
  19. the one nearest an end
  20. True
  21. False
  22. green-brown-brown
  23. 345
  24. 920
  25. saves electricity
  26. True
  27. 5 %
  28. 7.5
  29. 10
  30. 5
  31. 0.25
  32. 20
  33. 7
  34. 600
  35. gets smaller
  36. volt (V)
  37. less than either one
  38. 6
  39. 0.25
  40. 1.2

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