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Ch 25 Relevant Concept Questions

# Ch 25 Relevant Concept Questions - double Why or why not Is...

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University Physics Young and Freedman Chapter 25 Concept Questions and solutions Chapter 25: Pre-chapter Question Q: Is the amount of current that flows out of the flashlight bulb less than, greater than, or equal to the amount of current that flows into the bulb? A: Equal; current in = current out. 1. Suppose we replaced the wire in Example 25.1 with 12-g Cu wire, which has twice the diameter of 18-g wire. If the current remains the same, what is the new magnitude of the drift velocity? A: Reduce by ¼ since doubling diameter increases cross-sectional area by 4. 2. You maintain a constant electric field inside a piece of semiconductor while lowering the semiconductor's temperature. What happens to the current density in the semiconductor? A: Decreases based on graph. 3. Suppose you increase the voltage across the Cu wire in Examples 25.2 ans 25.3. The increased voltage causes more current to flow, which makes the temperature of the wire increase. If you double the voltage across the wire, does the current in the wire also
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Unformatted text preview: double? Why or why not? Is the wire ohmic? A: Current doubles, but resistance increases as well, so in effect, current is lower than a doubled value. Non-ohmic – ohmic means that V = I/R has the same value everywhere. 4. A battery has an Emf of 1.5 V and an internal resistance of 0.10 ohms. When the battery is connected to a resistor, the terminal voltage of the battery is 1.3 V. What is the resistance of the resistor? A: 1.3 = 1.5 – I(0.010); I = 2A; Terminal voltage of the battery is the voltage across the resistor; R = Vab / I = (1.3 V) / (2.0 A) = 0.65 Ohms 5. Repeat Example 25.9 for the idealized situation in which the source has no internal resistance. How do your answers compare to those in Example 25.9? A: r = 0; I = Emf / (R + r) = (12 V) / (4 Ohms + 0 Ohms) = 3 A. Rate of energy dissipation in the resistor = (I^2)R = 36 W....
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