Circuit Lab practice test: 30 questions you answer by measuring
- 192parts on the bench
- 25boards running now
- 1.00xreal time, on every board
These are 30 original practice questions for Science Olympiad Circuit Lab, grouped into ten sets of three. Each set comes with a circuit. Work the questions on paper first, then open the circuit, press Run and measure. If the meter and your paper disagree, one of them is right, and finding out which is the best practice there is.
The questions lean toward Division C, but sets 1 to 4 and 10 are fair game for a strong Division B team. Answers are at the bottom, all read off these circuits in the simulator. Moving a meter lead means dragging the end of its wire to a different pin; changing a value means clicking the part and editing it in the properties panel.
This is not an official test and it does not reproduce any Science Olympiad material. Check the current rules at soinc.org for what your division covers.
Set 1: Ohm's law (9 V, 470 ohms, meter on amps)
1. What current flows?
2. The supply is turned up to 12 V. What current flows now?
3. At 9 V, how much power does the resistor dissipate, and would a 1/8 W resistor be safe here?
Set 2: series (12 V into 1 k, 2.2 k and 3.3 k)
4. What is the voltage across the 2.2 k resistor?
5. What is the voltage across the 3.3 k resistor?
6. What current flows around the loop? Get it from one of your voltage readings, not from a formula.
Set 3: parallel (6 V across 1 k, 2 k and 3 k)
7. What total current does the supply deliver?
8. What current flows through the 2 k resistor alone?
9. What single resistor would draw the same total current?
Set 4: series-parallel (10 V, 1 k, then 2 k in parallel with 2 k)
10. What is the voltage across the parallel pair?
11. What current flows through the 1 k resistor?
12. What current flows through each 2 k resistor?
Set 5: Kirchhoff's laws (12 V and 6 V into one node)
13. What is the voltage at node A?
14. What current flows through the 1 k resistor?
15. What current flows through the 2 k resistor, and in which direction?
Set 6: a Wheatstone bridge
16. What does the meter read between the two middles, with R4 at 3.3 k?
17. What value of R4 makes the bridge balance (the meter reads zero)? Change R4 and check.
18. With the bridge balanced, what current flows through R3?
Set 7: RC charging (10 k and 100 uF from 5 V)
19. What is the time constant?
20. What is the capacitor voltage one time constant after you flip the switch?
21. What is it two seconds after you flip the switch?
Set 8: diodes (330 ohms from 5 V into a 1N4148 and a red LED)
22. What voltage drops across the silicon diode?
23. What voltage drops across the red LED, and what current flows in its branch?
24. Turn the silicon diode around. What does the meter read across it now, and why?
Set 9: capacitors in series (meter on capacitance, no supply)
25. What is the total capacitance of 1 uF and 2.2 uF in series?
26. Swap the 2.2 uF for the loose 4.7 uF. What does the meter read now?
27. Put all three in one series chain. Is the total bigger or smaller than the smallest one, and what is it?
Set 10: the meter is part of the circuit
28. Two 10 megohm resistors divide 10 V. What does the meter read across the bottom one?
29. Why is that not 5 V?
30. Change both resistors to 10 k. What does it read now, and why did the problem go away?
Answer key
1. 19.1 mA. 2. 25.5 mA. 3. About 0.17 W; no, that is more than 1/8 W (0.125 W). 4. 4.06 V. 5. 6.09 V. 6. 1.85 mA (the 1.85 V across the 1 k divided by 1 k).
7. 11.0 mA. 8. 3.00 mA. 9. About 545 ohms (6 V / 11.0 mA). 10. 5.00 V. 11. 5.00 mA. 12. 2.50 mA each.
13. 8.18 V. 14. 3.82 mA. 15. 1.09 mA, flowing from node A into the 6 V source, because node A is higher than 6 V. 16. -0.208 V (6.667 V on the left, 6.875 V on the right). 17. 3.0 k, so that R4 / R3 = R2 / R1. 18. 2.22 mA (10 V / 4.5 k).
19. 1.0 s (the scope’s 1 megohm makes it 0.99 s). 20. About 3.15 V, 63 percent of the way. 21. About 4.29 V. 22. 0.74 V. 23. 1.65 V and about 10.2 mA. 24. 5.00 V: reversed, the diode blocks, no current flows, so nothing else drops any voltage.
25. 0.688 uF. 26. 0.825 uF. 27. Smaller than the smallest: 0.600 uF. 28. 3.33 V. 29. The meter’s 10 megohms sit in parallel with the bottom resistor, making 5 megohms against 10. 30. 5.00 V (4.998 V): the meter barely loads 10 k.
Getting the most out of a practice run
Work it the way you will at a tournament. Set a timer, do the sets in order, and write every answer with its unit before you check the key. A number without a unit is an answer a grader can mark wrong.
Estimate before you measure. If a 9 V battery drives 470 ohms, the current has to be around 20 mA, so a reading of 2 mA or 200 mA means the meter is on the wrong range or in the wrong place. That habit catches more mistakes than rechecking the arithmetic does.
When you miss one, find out which kind of miss it was: the wrong formula, the right formula with a slip, or the meter set up wrong. Keep a short list of the kinds you miss, and you will know what to practice before the next run.
Questions
Can a coach assign these to a team?
Yes. Every set opens in the editor as its own circuit, so a coach with a class can assign one to the class and see each student’s saved work.
Why do some answers differ slightly from the textbook value?
Because the meter is modeled. Its 1 ohm current shunt and 10 megohm voltage input are part of the circuit, the same as on a real meter, and set 10 is built around that.
Build this for real
Open the editor, change a value and watch the number move with it. Nothing to install, and no account needed.