




Massachusetts Comprehensive Assessment System
2011, High School Intro Physics
Question 12: OpenResponse 

Reporting Category: Electromagnetism Standard: 5.2  Develop a qualitative and quantitative understanding of current, voltage, resistance, and the connections among them (Ohm's law).

An electrician places a variable resistor in series with an LED lamp and a 6 V battery, as shown below. LED lamps are efficient sources of light that operate at a specified voltage for a wide range of currents. The LED lamp in this circuit operates at a constant 3 V for all settings of the variable resistor, while the remaining 3 V is always dropped across the variable resistor. Calculate the current passing through the variable resistor when it is set to each of the values shown in the table below. Show your calculations and include units in your answers.
Voltage (V)  Resistance (O)  Current (A)  3.0  4   3.0  6   3.0  10   3.0  15   3.0  20  
 On the grid in your Student Answer Booklet, make a graph using your answers to part (a). Current should be on the yaxis and resistance should be on the xaxis. Clearly label the axes and use a proper scale.
 Based on the graph, describe what happens to the LED lamp as the resistance decreases.
The maximum recommended current for the LED lamp is 0.3 A. If the LED lamp is operated for a long time with the variable resistor set at 4 O, describe the most likely effect on the LED lamp.

Scoring Guide and Sample Student Work Select a score point in the table below to view the sample student response.
Score  Description 
4 
Response demonstrates a thorough understanding of the relationships between current, voltage, and resistance. The response correctly calculates the current values for each resistor value and correctly graphs current and resistance. The response also correctly describes what happens to the LED lamp as the resistance decreases and if the resistance is set at 4 Ω for a long time. 
4 
3 
Response demonstrates a general understanding of the relationships between current, voltage, and resistance. 
2 
Response demonstrates a limited understanding of the relationships between current, voltage, and resistance. 
1 
Response demonstrates a minimal understanding of the relationships between current, voltage, and resistance. 
0 
Response is incorrect or contains some correct work that is irrelevant to the skill or concept being measured. 
Note: There are 2 sample student responses for Score Point 4.
High School Intro Physics
 Question 12: Electromagnetism
 Question 23: Motion and Forces
 Question 32: Waves and Radiation
 Question 44: Motion and Forces
 Question 45: Heat and Heat Transfer
Return to the MCAS 2011 Student Work Directory
Last Updated: December 15, 2011


