Activity Measuring Current And Voltage Answer Key

Activity Measuring Current and Voltage Answer Key

Understanding how electric circuits behave is a fundamental skill for anyone studying physics, electronics, or engineering. The hands‑on activity described below lets students measure current and voltage in a simple series circuit, record their observations, and then compare the results to theoretical expectations using an answer key. By working through the experiment, learners reinforce Ohm’s law, practice using multimeters, and develop troubleshooting habits that are essential for real‑world circuit design.

Introduction

Measuring current (I) and voltage (V) is the cornerstone of circuit analysis. In this activity, students construct a basic series circuit with a power supply, a resistor, and an ammeter/voltmeter (or a digital multimeter capable of both functions). They then take readings at different points, calculate resistance, and verify that the relationship V = I × R holds within experimental error. The accompanying answer key provides the expected values, sample calculations, and guidance on interpreting discrepancies. This structured approach not only clarifies abstract concepts but also builds confidence in using measurement tools safely and accurately.

Understanding Current and Voltage

Before diving into the procedure, it helps to review the definitions:

• Current (I) – the flow of electric charge, measured in amperes (A). In a series circuit, the same current passes through every component.
• Voltage (V) – the electric potential difference between two points, measured in volts (V). It represents the energy per unit charge supplied by the source or dropped across a component.
• Resistance (R) – the opposition to current flow, measured in ohms (Ω). For a fixed resistor, R is constant and relates V and I through Ohm’s law: V = I × R.

Grasping these relationships prepares students to predict what the meter should read before they even connect the probes.

Materials Needed

Tip: Ensure the multimeter is set to the correct range before each measurement to avoid damaging the device.

Procedure (Steps)

1. Set up the power supply

   • Turn the supply off.
   • Connect the positive terminal to one end of the resistor using a breadboard wire.

2. Insert the ammeter

   • Break the circuit at the resistor’s free end.
   • Connect the multimeter’s red probe to the resistor lead and the black probe to the power supply’s negative terminal.
   • Set the multimeter to DC current (A), choosing a range that exceeds the expected current (e.g., 200 mA for a 220 Ω resistor at 5 V).

3. Measure the voltage across the resistor

   • Without changing the circuit, move the multimeter probes to the two ends of the resistor.
   • Set the meter to DC voltage (V), selecting an appropriate range (e.g., 20 V).
   • Record the voltage reading. 4. Vary the supply voltage
   • Increase the power supply output in steps (e.g., 2 V, 4 V, 6 V, 8 V, 10 V).
   • At each step, repeat steps 2 and 3 to obtain a new pair of (V, I) readings.

4. Calculate resistance

   • For each trial, compute R = V / I using a calculator.
   • Compare the calculated resistance to the nominal value (220 Ω).

5. Record all data

   • Create a table with columns: Supply Voltage (V_set), Measured Voltage (V_meas), Measured Current (I_meas), Calculated Resistance (R_calc), and Percent Error.

6. Safety check

   • After the final measurement, turn off the power supply and disconnect all leads.

Data Collection and Calculations

A typical data set might look like this (values are illustrative; actual results will vary slightly due to meter tolerance and resistor precision):

Sample calculation for the 6 V step: - V_meas = 5.94 V

• I_meas = 27.0 mA = 0.027 A
• R_calc = V / I = 5.94 V / 0.027 A ≈ 220 Ω

Percent error = |(R_calc − R_nominal) / R_nominal| × 100 % = 0 %.

Students should observe that the calculated resistance remains essentially constant, confirming the resistor’s ohmic behavior and validating Ohm’s law.

Answer Key Below is the answer key for the activity measuring current and voltage. Instructors can use it to check student work, provide feedback, or guide a discussion about sources of error.

Expected Results

1. Current readings should increase linearly with the supply voltage. For a 220 Ω resistor, the theoretical current at each voltage is I_theory = V_set / 220 Ω.

   • Example: At V_set = 8 V, I_theory = 8 V / 220 Ω ≈ 0.036 A = 36 mA. 2. Voltage across the resistor should closely match the supply voltage (within the meter’s accuracy), because the circuit contains only the resistor and the internal resistance of the supply is negligible.

2. Calculated resistance should fall within the tolerance band of the

Continuing the Answer Key and Conclusion

3. Calculated resistance should fall within the tolerance band of the resistor (e.g., ±5% for a 220 Ω resistor, resulting in a range of 209 Ω to 231 Ω). If the resistor’s actual value deviates from 220 Ω due to manufacturing tolerances, the calculated resistance will reflect this variation. Students should note that minor discrepancies (e.g., 215 Ω to 225 Ω) are acceptable and do not invalidate Ohm’s law.

4. Sources of error in the experiment may include:

   • Meter inaccuracies: Analog or digital meters may have limited resolution or calibration errors.
   • Contact resistance: Poor connections in the circuit could introduce additional resistance.
   • Supply voltage stability: Power supplies might fluctuate under load, affecting readings.
   • Human error: Misreading meters or recording data incorrectly.

Conclusion
This experiment demonstrates the practical application of Ohm’s law by systematically measuring voltage, current, and resistance in a simple circuit. The consistent calculated resistance values across varying voltages confirm the resistor’s ohmic behavior, aligning with theoretical predictions. Real-world factors such as meter precision and component tolerances introduce minor variations, but these do not undermine the validity of the relationship between voltage and current. By analyzing the data, students gain hands-on experience in scientific measurement, data interpretation, and understanding the principles governing electrical circuits. This foundational knowledge is critical for more complex electronics projects, where precise control and analysis of current and voltage are essential. The experiment reinforces the importance of methodical procedures, critical thinking, and recognizing the interplay between theory and real-world observations in scientific inquiry.