Electronics Worksheet: Components and Ohm’s Law Test

Electronics lesson 20: Part 2 test: components and Ohm’s law · Set 108 · 40 questions

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.

1. 1.💡 A blue LED uses 3 V and should get 25 mA. It runs from a 6 V supply. What resistor (in ohms) is needed in series?
2. 2.🔺 A current of 0.25 A flows through a 2 Ω resistor. What is the voltage across it (in volts)? =
3. 3.💡 Does it save or waste electricity to leave the TV on standby? (a) saves electricity (b) wastes electricity
4. 4.⚡ A device works on 12 V and takes 0.5 A. What is its power (in watts)? =
5. 5.⚡ A device works on 5 V and takes 0.5 A. What is its power (in watts)? =
6. 6.💡 A red LED (it uses 2 V) is joined with a 100 Ω resistor to a 3 V supply. What current flows (in mA)?
7. 7.🌈 Which colour bands (1st digit, 2nd digit, multiplier) mark an 890 Ω resistor? (a) white-grey-brown (b) grey-white-red (c) grey-white-black (d) grey-white-brown
8. 8.🔺 A 20 V supply is joined across a 500 Ω resistor. What current flows (in milliamperes, mA)?
9. 9.📏 How many kilo-ohms (kΩ) is 7000 Ω? =
10. 10.💡 What does LED stand for? (a) light energy dial (b) large electric dial (c) light-emitting diode (d) low energy device
11. 11.🔺 In the V-I-R triangle, how do we find I? (a) I = V + R (b) I = V ÷ R (c) I = V × R (d) I = R ÷ V
12. 12.🧾 A 75 W filament bulb is swapped for a 12 W LED lamp that gives about the same light. Both would run for 7 hours. How many watt-hours (Wh) are saved?
13. 13.💡 A blue LED uses 3 V and should get 20 mA. It runs from a 6 V supply. What resistor (in ohms) is needed in series?
14. 14.💡 Why does an LED need a resistor in series? (a) to change its colour (b) to make it brighter (c) to store charge (d) to limit the current
15. 15.Which of these saves electricity? (a) iron one shirt at a time (b) leave fridge door open (c) use LED lamps (d) run fans in empty rooms
16. 16.🔺 A current of 50 mA flows when 16.5 V is joined across a resistor. What is its resistance (in ohms)?
17. 17.🔺 A current of 2 A flows through a 6 Ω resistor. What is the voltage across it (in volts)? =
18. 18.⚡ A home appliance on the 230 V mains takes 1 A. What is its power (in watts)?
19. 19.🧾 One “unit” on an electricity bill is … (a) 1 kilowatt-hour (kWh) (b) 1 volt (c) 1 watt (d) 1 ampere
20. 20.True or false: a capacitor smooths a wobbly supply. (a) False (b) True
21. 21.🔺 A current of 10 mA flows when 1.5 V is joined across a resistor. What is its resistance (in ohms)?
22. 22.Which of these is measured in watts (W)? (a) resistance (b) current (c) energy used each second (d) voltage
23. 23.🧩 Which component makes a beeping sound? (a) buzzer (b) capacitor (c) thermistor (d) motor
24. 24.⚡ A device works on 9 V and takes 0.25 A. What is its power (in watts)? =
25. 25.📏 How many ohms (Ω) is 6.7 kΩ?
26. 26.⚡ A device works on 1.5 V and takes 1.5 A. What is its power (in watts)? =
27. 27.🌈 A gold fourth band on a resistor means the value may be off by … (a) 50 % (b) 0 % (c) 25 % (d) 5 %
28. 28.True or false: on an LED, the shorter leg is the anode (+). (a) True (b) False
29. 29.⚡ A home appliance on the 230 V mains takes 8 A. What is its power (in watts)?
30. 30.⚡ A device works on 9 V and takes 1.5 A. What is its power (in watts)? =
31. 31.True or false: to leave the TV on standby wastes electricity. (a) False (b) True
32. 32.🌈 In the resistor colour code, which number does grey stand for?
33. 33.True or false: a transistor boosts a small signal. (a) True (b) False
34. 34.Which of these saves electricity? (a) use old filament bulbs (b) leave the TV on standby (c) leave fridge door open (d) use daylight to read
35. 35.What does an LED do? (a) glows using little power (b) boosts a small signal (c) senses how bright it is (d) makes a beeping sound
36. 36.Which of these is measured in volts (V)? (a) the flow of charge (b) energy used each second (c) the push of a cell (d) current
37. 37.🔺 A current of 0.1 A flows through a 5 Ω resistor. What is the voltage across it (in volts)? =
38. 38.🧩 A capacitor in a circuit can … (a) measure heat (b) spin a wheel (c) make light (d) store charge briefly
39. 39.🌈 Which band is read first on a resistor? (a) the widest gap (b) the one nearest an end (c) any band (d) the gold band
40. 40.💡 A blue LED uses 3 V and should get 25 mA. It runs from a 5 V supply. What resistor (in ohms) is needed in series?

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