PHYS 2064
Chapter 17 Problems


Chapter Objectives
  1. Define electrical current.
  2. Define the resistance of an Ohmic object.  Describe the resistance in terms of the cross sectional area, length, and material composition of an object.
  3. Describe the change in the resistance of an object with temperature.
  4. Calculate the power delivered to a resistor.

Conceptual Problems

  1. If the drift velocity of electrons moving through a wire is so small, how come the light comes on almost immediately when you throw a switch?
  2. How does a dimmer switch work?
  3. Although high voltage lines are very thick, they are also very long. In going from the power plant to your house, the resistance of the line can be 1 ohm or greater. If the power company needs to deliver 10,000 watts of electricity to your house at 110 volts, how much power is lost to resistance?
  4. How much money do you spend yearly watching television? Reading a book, using a standard 75 watt bulb?

Problems

  1. In a particular television picture tube, the measured beam current is 6.0 x 10-5 A. How many electrons strike the screen every second?
  2. (a) A 34.5 m length of copper wire at 20.0 oC has a radius of 0.25 mm. If a potential difference of 9.0 V is applied across the length of the iwre, determine the current in the wire. (b) If the wire is heated to 30.0 oC, while the 9.0 V potential difference is maintained, what is the resulting current in the wire?
  3. A high voltage transmission line carries 1000 A at 700 kV for a distance of 160 km. If the resistance in the wire is 0.31 ohms/km, what is the power dissipated due to resistive losses?
  4. How much does it cost to watch a complete 21 hour long World Series on a 90.0 W black-and-white television set? Assume that electricity costs $0.0700/kWh.

Solutions

If you find an error in these, or just have a comment, send an e-mail message to jpratte@astate.edu