A filament lamp graph (typically plotting current against voltage) is curved because the resistance of the filament changes with temperature.
Here's a breakdown of why this happens:
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Resistance and Temperature: The resistance of a metal conductor, like the tungsten filament in a lamp, increases as its temperature increases.
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Heating Effect: When a voltage is applied across the filament, current flows through it. This current causes the filament to heat up due to the electrical energy being converted into heat energy. The higher the current, the hotter the filament becomes.
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Non-Linear Relationship: Because the resistance increases with temperature (and temperature increases with current), the relationship between voltage and current is not linear. Ohm's Law (V = IR) assumes a constant resistance. As the filament heats up, R changes, thus the linear relationship breaks down.
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Graph Explanation: At lower voltages, the filament is cooler, and its resistance is relatively low. As the voltage increases, the current also increases, causing the filament to heat up significantly. This increase in temperature leads to a substantial increase in resistance. Therefore, for each subsequent increase in voltage, the increase in current is less than it would be if the resistance remained constant. This causes the graph to curve, flattening out as the voltage and temperature rise.
In summary, the curve is a direct consequence of the temperature-dependent resistance of the filament material. The higher the temperature, the higher the resistance, leading to a smaller increase in current for each additional increase in voltage.
