PHYSICS HL

“To Investigate Ohm’s Law”

Aim:To find the relationship between the drop in Voltage (V) and the Current (I) for Ohmic and  Non-Ohmic resistors.

Data Collection:

Quantitative Data:

DCP Table 1.1 – Table showing the readings recorded when the bulb in air is connected in the circuit.

DCP Table 1.2 – Table showing the readings recorded when only the filament of the bulb immersed in water is connected in the circuit.

Qualitative Data:

As the voltage is increased the bulb begins to shine more brightly. After increasing it to over 14V (specified voltage of 12V), the filament blew and a new bulb had to be used and the entire experiment repeated.

The filament when immersed in water shows no significant change at lower voltages except for bubbles being evolved showing that the filament is hot. However,

• Must pass through the origin
• V and I must be directly proportional.

For Ohmic resistors,                                                    V=IR

Where V= Drop in Voltage, I = Current, R = Resistance.

DCP Graph  1.1 – Graph showing the plotted readings for the bulb filament immersed in water with the ammeter reading (A) on the y-axis and the voltmeter reading on the x-axis and line of best fit. Error bars cannot be shown as the magnitude of error ≈ (1 – 5)%  is insignificant on the graph.

Graphical Observations:

• The graph does not pass through the origin
• The plotted V-I values are directly proportional, with a slight deviation which can be accounted for by errors.

DCP Graph 1.2 – Graph showing the plotted readings for the bulb filament immersed in water with the ammeter reading (A) on the y-axis and the voltmeter reading on the x-axis and showing line of best fit. Error bars cannot be shown as the magnitude of error ≈ (1 – 5)%  is insignificant on the graph.

Graphical Observations:

• The graph passes through the origin
• The plotted V-I values are directly proportional, with a slight deviation which can be accounted for by errors.

Calculation of Resistance,

                ≈ R = 0.16 Ohms

Uncertainty Calculation:

                % Error in Voltmeter Reading =  x 100

                        = 12.5%

                % Error in Ammeter Reading =  x 100

                        = 2%

The formula for calculation of resistance imply standard temperature and pressure i.e. 273K and 1 atmosphere of pressure. However, my experiment was carried out in a temperature in excess of 403K accounting for a deviation from the actual value.

The Internal resistance of the battery source was not provided and hence it is an error that is not quantifiable.

The measuring apparatus i.e. the ammeter and the voltmeter are assumed to be ideal.

Random Error:

The experiment had to be re-done after the first light bulb filament blew due to an excess of voltage passing through it.

The readings of the apparatus consistently fluctuated, resulting in me using a mid-value between 2 fluctuating values.

Suggestions for Improvement:

A calibration of the apparatus so that the readings do not fluctuate.

A better comparison could have been the filament immersed in water V-I readings compared to a filament in air and the comparison of the effect of temperature on resistance. However, a filament glowing brightly in air is detrimental to our eyesight.

A comparison with a literature value would have lent a better understanding as to the accuracy of the experiment.

The experiment should have been carried out at standard conditions of temperature and pressure (i.e. 273K and 1 atm) in a controlled environment.