Electronics Worksheet: Components and Ohm’s Law Test

Electronics lesson 20: Part 2 test: components and Ohm’s law · Set 641 · 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 red LED (it uses 2 V) is joined with a 200 Ω resistor to a 3 V supply. What current flows (in mA)?
2. 2.Which of these wastes electricity? (a) switch off empty rooms (b) iron one shirt at a time (c) close the fridge quickly (d) use daylight to read
3. 3.🔺 A current of 25 mA flows when 3.75 V is joined across a resistor. What is its resistance (in ohms)?
4. 4.What does a fuse do? (a) senses how hot it is (b) blows if current is high (c) stores a little charge (d) smooths a wobbly supply
5. 5.True or false: a transistor smooths a wobbly supply. (a) False (b) True
6. 6.📏 How many ohms (Ω) is 0.9 kΩ?
7. 7.True or false: a resistor has coloured bands. (a) False (b) True
8. 8.📏 Voltmeter or ammeter: which one measures current? (a) voltmeter (b) ammeter
9. 9.🔺 A current of 20 mA flows through a 500 Ω resistor. What is the voltage across it (in volts)? =
10. 10.⚡ A home appliance on the 230 V mains takes 1 A. What is its power (in watts)?
11. 11.🌈 A resistor has the colour bands white, black, red. What is its value in kilo-ohms (kΩ)? =
12. 12.True or false: on an LED, the round-side leg is the cathode (−). (a) False (b) True
13. 13.🔺 A current of 0.1 A flows through a 15 Ω resistor. What is the voltage across it (in volts)? =
14. 14.🧮 A 10 Ω resistor is joined in series with two equal 40 Ω resistors that are in parallel with each other. What is the total resistance (in ohms)?
15. 15.💡 What does LED stand for? (a) light energy dial (b) large electric dial (c) light-emitting diode (d) low energy device
16. 16.🔺 A current of 1 A flows through a 2 Ω resistor. What is the voltage across it (in volts)? =
17. 17.🔺 A current of 50 mA flows when 15 V is joined across a resistor. What is its resistance (in ohms)?
18. 18.📏 Which unit measures the push of a cell? (a) watt (W) (b) ampere (A) (c) ohm (Ω) (d) volt (V)
19. 19.🔺 The voltage stays the same and the resistance gets bigger. The current … (a) gets bigger (b) stays the same (c) becomes zero (d) gets smaller
20. 20.🧩 A capacitor in a circuit can … (a) spin a wheel (b) measure heat (c) store charge briefly (d) make light
21. 21.⚡ An 18 W device works on 9 V. What current does it take (in amperes)? =
22. 22.🌈 A gold fourth band on a resistor means the value may be off by … (a) 0 % (b) 5 % (c) 25 % (d) 50 %
23. 23.⚡ Power tells us … (a) the colour of light (b) the length of a wire (c) the size of a cell (d) energy used each second
24. 24.🌈 A resistor has the colour bands brown, black, red. What is its value in kilo-ohms (kΩ)? =
25. 25.🌈 A resistor has the colour bands yellow, black, orange. What is its value (in ohms)?
26. 26.🌈 In the resistor colour code, which number does violet stand for?
27. 27.⚡ Which formula gives electric power? (a) P = V + I (b) P = V ÷ I (c) P = I ÷ V (d) P = V × I
28. 28.🧮 Two equal 40 Ω resistors are joined in parallel. What is the total resistance (in ohms)?
29. 29.🔺 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
30. 30.🔍 Which is the odd one out? (a) close the fridge quickly (b) switch off empty rooms (c) use LED lamps (d) leave fridge door open
31. 31.💡 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?
32. 32.🌈 Which band is read first on a resistor? (a) the gold band (b) the widest gap (c) the one nearest an end (d) any band
33. 33.🧮 Two equal 470 Ω resistors are joined in parallel. What is the total resistance (in ohms)?
34. 34.🌈 A resistor has the colour bands red, orange, red. What is its value (in ohms)?
35. 35.🔺 A current of 50 mA flows through a 330 Ω resistor. What is the voltage across it (in volts)? =
36. 36.📏 How many ohms make 1 kilo-ohm (kΩ)? (a) 100 (b) 1024 (c) 10 (d) 1000
37. 37.True or false: on an LED, the leg by the flat edge is the anode (+). (a) True (b) False
38. 38.💡 Why does an LED need a resistor in series? (a) to store charge (b) to limit the current (c) to make it brighter (d) to change its colour
39. 39.🔺 A 20 V supply is joined across a 500 Ω resistor. What current flows (in milliamperes, mA)?
40. 40.🔺 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

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