PHYS1230 Name: Date Practice 19: Current, Resistance, & EMF 1. A wire of resistance R is stretched uniformly (keeping its volume constant) until it is twice its original length. What happens to the resistance? [A] it increases by a factor 2 [B] it increases by a factor 4 [C] it stays the same [D] it decreases by a factor 4 [D] it decreases by a factor 2 Hint: It should be quite clear that we must use equation R-PL/A. Pay attention to the phrase "keeping its volume constant". 2. If the voltage across a resistor is doubled, which of the following is true? [A] The power dissipated by the resistor doubles and the resistance doubles. [B] The power dissipated by the resistor quadruples and the resistance doubles. [C] The power dissipated by the resistor doubles and the resistance is unchanged. [D] The power dissipated by the resistor quadruples and the resistance is unchanged 3. A battery has an emf of 10.0 V and an internal resistance of 1.0 2. For what external resistance connected across the 10.0 V battery will the total dissipated power (in the internal and external resistances) be 20.0 W? r=1.0 0 R