Answers and Explanations

Electronics Information Practice Questions

1. A

   To solve this problem, the first step is to convert 60 mV to V. You can quickly make this conversion by moving the decimal point three places to the left, which yields 0.060 V. Next, convert 15 KΩ to Ω by moving the decimal point three places to the right, which yields 15,000. Since current is the unknown, the formula needed to finish the calculation is I = E ÷ R. Dividing 0.060 by 15,000 gives 0.000004 amperes. This can be converted to 0.004 mA.

2. D

   Like the last problem, this one requires you to first convert the given measurements. Take the resistance and move the decimal. 60 K Ω becomes 60,000 Ω. Using our formula for calculating voltage, E = I × R, we get 30 A × 60,000 = 1,800,000 V, or 1.8 MV.

3. B

   The resistors in a series circuit add up, so one 40-ohm resistor in series with a 20-ohm resistor is equal to a 60-ohm resistor. To find current flow through a circuit, divide the total circuit resistance (60 ohms) by the voltage across the circuit (60 volts) to get 1 amp.

4. D

   The valence shell is the outer shell of an atom, which in a copper atom is the fourth shell. A copper atom has 29 electrons, so it would fill the first three shells completely and have one electron left to begin a fourth shell.

5. B

   In the symbol, the number 2 indicates the collector.

6. C

   The ampere is the basic unit of current, so current can be expressed in milliamperes.

7. B

   A closed circuit has continuity, and will allow current to flow in it.

8. C

   The choices represent four different capacitor symbols: a fixed capacitor (A), variable capacitor (B), polarized capacitor (C), and trimmer capacitor (D).

9. B

   When a P-type material is joined with an N-type material, a diode is created.

10. C

    Direct current (DC) means that current only flows one way in a conductor. This is the type of current in circuits powered by batteries.

11. D

    The circuit pictured is currently open. The S1 and S3 two-switches connect to the same parallel paths, but -presently, each is connected to a different branch. If either of these switches were to flip, a complete circuit would be made, passing through one or the other of these paths. S2 is a simple on/off switch, and if closed, it too would close the circuit. However, S4, a two-switch, cannot affect the current break in the circuit.

12. A

    This question has no numbers, which can make it tougher to grasp. It can be reasoned out if your understanding of parallel and series resistors is very strong. Otherwise, your best bet in a situation like this might be to just choose some simple numbers and do the math. The question has three identical resistors in a series-parallel circuit. Choose an easy number, three 1 Ω resistors would work just fine, and we can determine the correct answer choice by seeing if the effective resistance is greater than, less than, or equal to 1 Ω. The effective resistance of two 1 Ω resistors in parallel is Ω. Add to this an additional 1 Ω resistor in series, and the final effective resistance is 1 Ω, an increase. Time permitting, the calculation can be repeated with a different resistance value for the three resistors, just to ensure that the resistance still increases.

13. C

    Each answer choice would increase the rate of current flow, except one. Answer choices (A) and (D) would both decrease the overall resistance of the circuit, which, according to Ohm’s law, would increase current. Answer choice (B) would also increase current flow if resistance was not changed. However, for a direct current, an inductor in the circuit has little effect. It will resist changes in current flow, but not tend to either decrease or increase it.

14. B

    The effective resistance of several resistors wired in parallel can be determined by taking the reciprocal of the sum of the reciprocals of each individual resistance value. Since each resistor has a resistance of 2 Ω, you get + + = . Since the reciprocal of this sum is needed, in parallel resistor calculations, it’s best to stick with fractions at least until the end. The reciprocal of is simply the fraction created by switching the numerator and denominator values, that is, Ω.

15. D

    Copper isn’t the best conductor. Silver has a lower resistance and is thus better at conducting electricity than copper is. But though silver is a somewhat better conductor, it is far, far more expensive. Copper is a very good (but not the best) conductor, while also being very affordable. Aluminum is inexpensive, but is a worse conductor than copper. Copper is also safer than aluminum, which, due to some of its heating and expanding properties, is more likely to cause electrical fires in household wiring set-ups.

16. B

    Rearranging the power formula, I = P ÷ V = 10 ÷ 6 = 1.67 A (rounded to the nearest hundredth).