Physics lab report

Experiment 8 - Resistance and Ohm’s Law 

8.1 Introduction 

In previous experiments, we have investigated electric charges largely under stationary conditions. These                         

studies were useful in order to illustrate concepts such as ​the ​electric potential and ​the electric field​, and                                   

forms the foundation needed to further our understanding of electricity and electrical circuits. In contrast                             

to electrostatics (charges confined to be stationary), the field of electricity deals with the flow (induced                               

movement) of electrical charges. Due to its many uses, most individuals knowingly or unknowingly have                             

a daily reliance on electricity. It is especially essential, in: (1) the distribution of energy, and (2) the                                   

processing of information. To enable this, electricity must be handled in circuits, a closed loop of                               

conducting wire connecting power plant with individual homes, and businesses. To appreciate this                         

phenomena, it is useful to investigate various aspects of simple circuits and the various laws that may                                 

govern them. 

 

 

8.2 Objective  

1. To verify Ohm’s Law 

2. To use Ohm’s law to determine the resistance of a light source. 

 

 

8.3 Theory 

Our initial investigations will be guided by Ohm’s law, which postulates that the relationship between                             

current flow ​I​, potential difference ​V​, and resistance ​R for certain materials will observe the following                               

mathematical relationship, given a constant temperature constraint: 

…………. 1RV = I  

These materials are called Ohmic conductors, equation 1 implies that the ratio of voltage to current for                                 

these materials is constant. Manufactured resistors can be considered as such, but other components such                             

as semiconductor diodes, filaments, and LEDs are non ohmic. In this experiment, we will verify Ohm’s                               

law by assessing whether it holds for a set resistance (typical color coded resistor). Further, we will apply                                   

this to ascertain the resistance of a light source. 

 

8.4 Apparatus 

Variable DC voltage source,   color coded resistor,    (2) multimeters,  connecting wires,   light source 

 

 

8.5 Procedure  

Part A ­ Verifying Ohm’s Law  1. You will be given a particular colour coded resistor from the set; use this and the other apparatus                                   

items to set up the circuit as shown in figure 1 below. 

  Figure 1 

  2. Adjust DC voltage source so that a relatively small voltage reading is seen across the resistor R.                                 

Record this voltage reading, and the electrical current reading passing through the resistor.  Your multimeter devices must be properly set to make these measurements. 

3. Repeat step 2 with increasingly larger voltage values until you have 9 rows of data.  4. Plot a graph of  current (y­axis) vs voltage.  5. Use your graph to determine an experimental value of the resistance used.  6. Perform an error analysis on experimental and actual resistance values to determine the                         

effectiveness of the theory used. 

  Part B ­ Determining the resistance of a light source  1. Replace the given resistance in the circuit above with the light source provided.  2. Repeat steps 2 ­ 5 from part A above to deduce the resistance of the light source. 

 

8.6 Report Write-up   

In your discussion/conclusion, ensure to include:   

● a summary of whether you believe experiment results agrees with theory, and why;  

● possible sources of error (at least two), and precautions taken; 

● ways in which the experiment could be improved.