# To investigate whether the two resistors and the bulb given is an ohmic or non-ohmic conductor.

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Introduction

Ohmic Conductors (ELC)

Physics Portfolio By Clement Ng 12.6

Aim: To investigate whether the two resistors and the bulb given is an ohmic or non-ohmic conductor.

Method:

- Arrange apparatus as shown in the below circuit diagram
- Replace R with the tested unknown resistor or bulb
- Adjust the variable power supply until volt meter reads of consecutive even numbers, 2, 4, 6…12
- In each case, record down the corresponding current value on the amp meter
- After the first set of readings are collected, redo the experiments to obtain some check readings
- Repeat method until all the two resistors and the bulb is tested
- Using the results, calculate the averages and plot graphs of V against I, remember to include the error bars
- Using the graphs, work out the max/min/normal gradients and calculate the resistance for each item. Remember to specify the error in the final resistance value by using the max/min gradient values.
- Compare the graph of a resistor and a light bulb and comment on the behavior
- Write conclusions and evaluations

Middle

2.30

2.31

12.0

2.54

2.50

Skill 4 Data Processing

Resistor 1 (#8):

Voltage (v) (± 0.5V) | Average Current (A) (± 0.005A) | ||

Minimum Error | Normal | Maximum Error | |

2.0 | 0.025 | 0.030 | 0.035 |

4.0 | 0.065 | 0.070 | 0.075 |

6.0 | 0.100 | 0.105 | 0.110 |

8.0 | 0.135 | 0.140 | 0.145 |

10.0 | 0.175 | 0.180 | 0.185 |

12.0 | 0.210 | 0.215 | 0.220 |

Resistor 2 (#3):

Voltage (v) (± 0.5V) | Average Current (A) (± 0.005A) | ||

Minimum Error | Normal | Maximum Error | |

2.0 | 0.095 | 0.100 | 0.105 |

4.0 | 0.195 | 0.200 | 0.205 |

6.0 | 0.295 | 0.300 | 0.305 |

8.0 | 0.395 | 0.400 | 0.405 |

10.0 | 0.495 | 0.500 | 0.505 |

12.0 | 0.595 | 0.600 | 0.605 |

Light Bulb

Voltage (v) (± 0.5V) |

Conclusion

Improvement 2:

Since we know that there is an internal resistance in the amp meter/ volt meter, we could test these apparatus in order to find the effects of this internal resistance on the final current and voltage values. To do this, we could connect the amp meter/ volt meter, to a known current and voltage and see how much the meter values are off by. We could then take this current and voltage correction and add them onto our experimental values. That way, we could easily correct the error the internal resistance in our apparatus has made towards our final results.

Improvement 3:

To improve on graph plotting and tangent drawing skills, we could use a computer to help us. Many computer software’s nowadays can help us draw tangents or even help us calculate the gradient directly. After the experimental results are obtained, simply copy them into the program and plot graphs of V/I. These graphs would be much more accurate then hand plotted ones, and resistance values would be calculated to the highest degree of accuracy.

Unfortunately, allowing the computer to do the job for you does not show any skill in data processing. Thus another improvement can be done by using calculus. Calculus is a good tool in mathematics to calculate the gradient of a known equation. Simply obtain the equation of the line/curve and perform differentiation, then you’ll get a gradient value that would possibly be even more accurate then a computer value!

By Clement Ng 12.6

Sunday, June 16 2002 03:37AM

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This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

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