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3_Resistance - heat to glow • Why we use a thin wire in a...

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1 Resistance • Resistance • Resistivity Water Analogy What can be done to a pipe to increase the resistance to flow of water? Decrease the diameter of the pipe If resistance to the flow of water increases, what happens to the overall current? - Current decreases Relation to Resistance The same is true for Electricity. Opposition to motion of charge through a conductor is resistance . Factors affect resistance through a circuit. – The kind of metal (conductivity). – Length of wire (longer = greater resistance). – Thickness of the wire ( thicker = less resistance). – Temperature (higher = greater resistance). Resistance can cause heat and light Electrical resistance is friction in the wire. Measured in Ohms ( Ω ) Electrical resistance causes warming or enough
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Unformatted text preview: heat to glow. • Why we use a thin wire in a light bulb: more resistance, hotter faster. 2 The light bulb • Tungsten wire - high resistance causing it to glow white-hot. • Also, tungsten doesn't burn up as fast, so lasts longer. • Schematic symbol: Resistance and Resistors • Wires – relatively low resistance. • Resistors- designed to have a specific resistance; reduces the amount of current. • Schematic symbol: Potentiometer • Variable resistor that gives a smooth continuous change in current. –Dimmer on a light –Speed adjustment on fan. –Volume adjustor on TV Resistance and Your Body • Dry Skin: 500,000 Ω • Wet Skin: 100 Ω • Rubber soles of shoes can resist 120V; but wet feet on bathroom floor cannot. 3...
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