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Transcript
What happens connect the two ends of a battery with a wire? • The negative terminal of the battery acts as though it has too many electrons. That is, it acts like it is negatively charged. So, the negative terminal of the battery pushes electrons in the wire away and toward the positive terminal. • In a closed loop, the result is a flow of electrons through the wire. Electric Current Electric current (or just current) is the rate at which charges (electrons) flow through a wire. More generally, currently is the rate at which charges flow through a surface. The unit for current is the Amp 1 A=1 C/s The symbol for current is i The current through a circuit (and so through the battery) changes when we change the number of bulbs in the circuit or how they are arranged. Bulbs present an obstacle (or resistance) to the flow of current. Bulbs Don’t Use Up Current • Why do batteries go “dead”? For a given battery: • The current is the circuit is not always the same. • More resistance in the circuit, current in the circuit. • Less resistance in the circuit, current. For a given battery: • The current is the circuit is not always the same. • More resistance in the circuit, less current in the circuit. • Less resistance in the circuit, more current in the circuit. • Does adding bulbs increase or decrease the total resistance in the circuit? More Bulbs Changes the Total Resistance in the Circuit • Adding bulbs in series increases the resistance. • Adding bulbs in parallel decrease the resistance. Resistors in Combination • Resistors in Series R = R1 + R2 • Resistors in Parallel 1 1 1 R R1 R2 For a given battery: • The current is the circuit is not always the same. • More resistance in the circuit, less current in the circuit. • Less resistance in the circuit, more current in the circuit • What stays the SAME about the battery is its “the strength of its push”. VOLTAGE,CURRENT AND RESISTANCE Voltage is the word we use for the “strength of the push” V=IR If Voltage of the battery stays constant, and the resistance of the circuit increases, the current must decrease.