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Resistance Investigation

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Introduction

Physics coursework Hypothesis-I predict that the resistance of the resistors can be found by dividing the voltage by the current through the resistor. It can be found by finding the gradient of the best-fit line on the graph of voltage against current. This will happen because the voltage and current are proportional so voltage will equal constant current. The constant term is the resistance so the resistance is voltage divided by current. The gradient on the graph can be formed by dividing the unit on the y-axis by the unit on the x-axis which will be voltage divided by current or on the filament lamp graph it will be current divided by voltage. The gradient will depend on the resistance of the resistors. Ohm's law will be followed if the graph is a straight line through the origin, so this can be used to prove Ohm's law is valid. Background Information- Current is the flow of charge. ...read more.

Middle

Copper is a good conductor and as temperature increases, the resistance of a wire increases. Voltage graphs are different like the graph of an ohmic conductor is a straight line that passes through the origin; this shows that it obeys Ohm's law. The graph of the filament lamp is a non-ohmic conductor as it is a curve and clearly does not obey Ohm's law. As more current flows, the metal filament gets hotter and so its resistance increases this means the graph gets flatter. A thermistor is used in electronics and is made of a semi-conductor substance. As more current flows, the thermistor gets hotter and so its resistance decreases so the graph gets steeper. Method - Connect a power supply to the resistor and an ammeter in series and connect a voltmeter. Measure the current at volt intervals of 0.5 up to 5 volts. The test will be kept fair by making sure the temperature is kept constant, make sure that current is measured every 0.5 volts and other ways of keeping the test fair. ...read more.

Conclusion

Yes the temperature is kept constant as the same wire is used. The blue resistor needs the most energy as it has the highest resistance. The Filament lamp graph is a steep curved shape. It is this shape because the voltage increases as the current does not increase as much. The filament bulb has a high resistance so the electrons are stopped often and a lot of energy is released. This causes the filament to become hot and begins to glow, releasing light. The heat then causes the resistance to increase even more because the particles are vibrating faster and will stop the electrons more often. Therefore, a higher voltage is needed to allow the same current through or a lower current will pass at the same voltage. The filament lamp does not obey ohm's law, as the voltage across the bulb is not proportional to the current. This proves that ohm's law is correct in saying voltage and current are proportional at a constant temperature as the filament bulb gets hotter and does not obey ohm's law, therefore, it is not an ohmic conductor. ...read more.

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