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Kristin Fracchia

ACT Challenge Question 20: Total Resistance

Magoosh ACT Challenge Question


This week, we have another ACT Science challenge question for your test prep enjoyment! Can you conquer it? The question is based on the ACT Science Research Summaries Passage you will see below the question. Post your answer and how you got it in the comments below, and then check back for the answer on Friday!


ACT Science Research Summaries Challenge Question

The total resistance in a circuit for resistors connected in series is the sum of their individual resistances. Suppose the student rewired the circuit with a 3.0 ohm and a 6.0 ohm resistor in series, using a 3.0 V battery to supply the voltage. What current would an ammeter placed in this circuit most likely read?

A. 0.333 amps

B. 0.667 amps

C. 1.333 amps

D. 1.500 amps


ACT Science Research Summaries Challenge Passage

In a simple DC electrical circuit, a battery provides a change in voltage (V) that induces an electric current (I) through the circuit. A conductor placed in the circuit is characterized by its resistance (R) to this flow of electric charge. The relationship between voltage, current, and resistance is known as Ohm’s Law, which is represented by the following formula:

V = I × R

A student performed a series of experiments with a simple circuit to test Ohm’s law. Measurements of current were taken using an ammeter. The circuit diagram is presented in Figure 1.

Figure 1


Experiment 1

            The student set up a simple circuit consisting of a battery and a single resistor. The resistor was taken from an electronics kit and wired into the circuit. Using an ammeter, the student measured current in the circuit for batteries of three different voltages and recorded the results in Table 1.


Experiment 2

Using the same circuit as in the previous experiment, the student tried three different resistors. The current flowing through the circuit with each resistor was measured with an ammeter, and recorded in Table 2.


Experiment 3

To test the electrical resistance of some common battery-operated appliances, the student set up a simple circuit consisting of a 15.0-volt battery and a socket to plug in the appliance. The current was measured using an ammeter and recorded in Table 3.



About Kristin Fracchia

Kristin makes sure Magoosh's blogs are chock-full of awesome, free resources for students preparing for standardized tests. With a PhD from UC Irvine and degrees in Education and English, she’s been working in education since 2004 and has helped students prepare for standardized tests, as well as college and graduate school admissions, since 2007. She enjoys the agonizing bliss of marathon running, backpacking, hot yoga, and esoteric knowledge.

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