ACT science practice test 51

Directions: Each passage is followed by several questions. After reading a passage, choose the best answer to each question and fill in the corresponding oval on your answer document. You may refer to the passages as often as necessary.

You are NOT permitted to use a calculator on this test.


Every time a lightbulb is switched on, an electrical circuit is formed. When plugged into outlets that provide a certain voltage, current begins to flow through the bulbs. Current depends on the resistance of the bulb and the voltage of the power supply. The power output of a bulb is a measure of the amount of energy the bulb requires each second. Power is calculated by multiplying current and voltage. Table 9.3 contains data that relate these variables for a basic circuit consisting of one lightbulb and a power supply.

TABLE 9.3

Figure 9.2 shows three configurations of bulbs. When the bulbs are connected in series, they form one path to the power supply. If any bulb in the pathway breaks, all the lights go out because the circuit is no longer complete. In contrast, bulbs connected in parallel are all independently connected to the power supply-in essence, forming their own circuits. Bulbs wired in parallel across a power supply continue to work even when one bulb goes out because each branch forms an independent circuit.

Figure 9.2

Table 9.4 shows how the number of bulbs in series and parallel affect the current and power values. It gives data for 240-ohm bulbs connected to a 120-V power supply.

TABLE 9.4

1. Based on the data in Table 9.3, describe the relationship between current, voltage, and resistance.

A. Current is the ratio of voltage to resistance.
B. Current is the product of voltage and resistance.
C. Current is the ratio of resistance to voltage.
D. Current is proportional to the square of voltage and independent of resistance.

2. Using information provided in the passage, determine the power output of a 50.0-ohm bulb connected to a 150-V socket that has 3.0 A flowing through it.

A. 3 W
B. 50 W
C. 150 W
D. 450 W

3. For a fixed voltage, what happens to the power output of a bulb when its resistance triples?

A. The power triples.
B. The power increases by a factor of 9.
C. The power decreases to one-third of its value.
D. The power decreases to one-ninth of its value.

4. For a bulb with a given resistance, what happens to the flow of current through the bulb when the voltage of the power supply doubles?

A. The current doubles.
B. The current quadruples.
C. The current decreases to one-half its value.
D. The current decreases to one-fourth its value.

5. A 480-ohm bulb is screwed into a 120-V socket. How much energy does it need to stay lit for four hours?

A. 108 kJ
B. 120 kJ
C. 216 kJ
D. 432 kJ

6. Predict the power required to operate a 600-ohm light bulb when it is plugged into a 120-V outlet.

A. 20 W
B. 24 W
C. 30 W
D. 120 W

7. According to Tables 9.3 and 9.4, when a fifth bulb is added to a parallel circuit, each bulb will:

A. output the same amount of energy per second as a bulb in a basic circuit.
B. output more energy per second than a bulb in a basic circuit.
C. output less energy per second than a bulb in a basic circuit.
D. make the other bulbs get brighter.

8. When a fifth bulb is added to a series circuit, how will the bulb's power output compare to that of a bulb in a four-bulb series circuit?

A. It will produce the same amount of power.
B. It will produce twice the power.
C. It will produce less power.
D. It will produce no power.

9. According to the information in Tables 9.3 and 9.4, adding an additional bulb to a parallel circuit:

A. increases the circuit's power output by decreasing the total resistance of the entire circuit.
B. decreases the circuit's power output by decreasing the total resistance of the entire circuit.
C. increases the circuit's power output by increasing the total resistance of the entire circuit.
D. decreases the circuit's power output by increasing the total resistance of the entire circuit.

10. The circuit in Figure 9.3 shows Bulbs 2 and 3 wired in parallel. That combination is wired in series with Bulb 1 and the battery. Which of the following statements is FALSE?


Figure 9.3

A. If Bulb 1 breaks, the other two bulbs will go out.
B. If Bulb 2 breaks, the other two bulbs will go out.
C. If both Bulbs 2 and 3 break, Bulb 1 will go out.
D. If Bulb 3 breaks, the other bulbs will stay lit.

11. As bulbs are added to a parallel circuit:

A. more current flows through each bulb.
B. less current flows through each bulb.
C. less power is output from the circuit.
D. more current flows through the battery.

12. A child noticed that five bulbs in her electric toy went out simultaneously, but four other bulbs remained lit. What is the most likely circuit arrangement in the toy?

A. The five bulbs that went out are wired in parallel.
B. Each of the five bulbs that went out are broken.
C. The five bulbs that went out are wired in series.
D. All nine bulbs are wired in parallel.

13. Adding additional bulbs to a series circuit:

A. increases the resistance of the entire circuit.
B. decreases the resistance of the entire circuit.
C. decreases the power output of the entire circuit.
D. increases the flow of current in each bulb.

14. A watt (W) of power is the total joules (J) of electrical energy transferred by a circuit element each second. Given a circuit with three 240-ohm bulbs wired in series to a 120-V power supply, how much energy is transferred by the circuit if it operates for 10 seconds?

A. 6.7 J
B. 67 J
C. 150 J
D. 200 J

15. How much power does a parallel circuit require if it has six 240-ohm resistors connected to a 120-V power supply?

A. 60 W
B. 120 W
C. 360 W
D. 1,440 W