Electronics Worksheet: Components and Ohm’s Law Test

Electronics lesson 20: Part 2 test: components and Ohm’s law · Set 500 · 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.💡 What happens if an LED is put in backwards? (a) it makes a sound (b) it changes colour (c) it does not light (d) it lights brighter
2. 2.📏 How many milliamperes (mA) is 2.72 A?
3. 3.💡 A red LED (it uses 2 V) is joined with a 100 Ω resistor to a 3 V supply. What current flows (in mA)?
4. 4.🧮 Resistors of 47 Ω, 22 Ω and 68 Ω are joined in series. What is the total resistance (in ohms)?
5. 5.⚡ Which formula gives electric power? (a) P = V + I (b) P = I ÷ V (c) P = V ÷ I (d) P = V × I
6. 6.🔺 A 24 V supply is joined across an 8 Ω resistor. What current flows (in amperes)? =
7. 7.🧩 Which component has coloured bands? (a) LDR (b) resistor (c) motor (d) diode
8. 8.Which of these wastes electricity? (a) set the AC to 24 °C (b) leave the TV on standby (c) use daylight to read (d) close the fridge quickly
9. 9.🔺 A current of 2.5 A flows when 25 V is joined across a resistor. What is its resistance (in ohms)?
10. 10.What does an LDR do? (a) beeps for an alarm (b) senses how bright it is (c) lets current go one way (d) stores a little charge
11. 11.💡 An LED is joined to a 3 V battery through a 330 Ω resistor; its long leg goes to the − side and its short leg to the + side. What happens? (a) lights up (b) does not light (c) may burn out
12. 12.🌈 Which band is read first on a resistor? (a) the gold band (b) the one nearest an end (c) any band (d) the widest gap
13. 13.⚡ A home appliance on the 230 V mains takes 5 A. What is its power (in watts)?
14. 14.💡 Does it save or waste electricity to run fans in empty rooms? (a) saves electricity (b) wastes electricity
15. 15.🧮 Adding another resistor in series makes the total resistance … (a) smaller (b) stay the same (c) zero (d) bigger
16. 16.🔺 A 6.6 V supply is joined across a 330 Ω resistor. What current flows (in milliamperes, mA)?
17. 17.🧾 A 100 W filament bulb is swapped for a 15 W LED lamp that gives about the same light. Both would run for 9 hours. How many watt-hours (Wh) are saved?
18. 18.True or false: a buzzer turns a fan or wheels. (a) False (b) True
19. 19.📏 Which unit measures resistance? (a) ampere (A) (b) volt (V) (c) ohm (Ω) (d) watt (W)
20. 20.💡 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?
21. 21.⚡ A 0.375 W device works on 1.5 V. What current does it take (in amperes)? =
22. 22.🧮 Two equal 200 Ω resistors are joined in parallel. What is the total resistance (in ohms)?
23. 23.🧩 Which component senses how bright it is? (a) motor (b) LDR (c) capacitor (d) diode
24. 24.🌈 In the resistor colour code, which number does blue stand for?
25. 25.💡 An LED is joined to a 3 V battery through a 330 Ω resistor; its long leg goes to the + side and its short leg to the − side. What happens? (a) lights up (b) may burn out (c) does not light
26. 26.⚡ Power tells us … (a) the colour of light (b) the size of a cell (c) the length of a wire (d) energy used each second
27. 27.🔺 A 3.3 V supply is joined across a 330 Ω resistor. What current flows (in milliamperes, mA)?
28. 28.🔺 In the V-I-R triangle, how do we find I? (a) I = V × R (b) I = V + R (c) I = R ÷ V (d) I = V ÷ R
29. 29.📏 Which unit measures energy used each second? (a) ohm (Ω) (b) ampere (A) (c) watt (W) (d) volt (V)
30. 30.📏 Voltmeter or ammeter: which one is joined in series? (a) ammeter (b) voltmeter
31. 31.🔺 In the V-I-R triangle, how do we find R? (a) R = V × I (b) R = V + I (c) R = I ÷ V (d) R = V ÷ I
32. 32.🔺 In the V-I-R triangle, how do we find V? (a) V = I × R (b) V = I + R (c) V = I ÷ R (d) V = R ÷ I
33. 33.🧮 Five equal 50 Ω resistors are joined in parallel. What is the total resistance (in ohms)?
34. 34.🔺 A current of 0.1 A flows when 0.8 V is joined across a resistor. What is its resistance (in ohms)?
35. 35.🧮 A 6.5 V battery is joined to 3 Ω and 10 Ω resistors in series. What current flows (in amperes)? =
36. 36.⚡ A device works on 3 V and takes 1 A. What is its power (in watts)? =
37. 37.🔍 Which is the odd one out? (a) close the fridge quickly (b) leave fridge door open (c) run fans in empty rooms (d) use old filament bulbs
38. 38.🌈 Which colour bands (1st digit, 2nd digit, multiplier) mark a 7400 Ω resistor? (a) violet-yellow-orange (b) violet-yellow-red (c) violet-yellow-brown (d) yellow-violet-red
39. 39.🔺 A current of 20 mA flows through a 150 Ω resistor. What is the voltage across it (in volts)? =
40. 40.💡 On an LED, is the leg by the flat edge the anode (+) or the cathode (−)? (a) cathode (−) (b) anode (+)

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