Ch 25: Resistors & DC CircuitsSee all chapters
All Chapters
Ch 01: Units & Vectors
Ch 02: 1D Motion (Kinematics)
Ch 03: 2D Motion (Projectile Motion)
Ch 04: Intro to Forces (Dynamics)
Ch 05: Friction, Inclines, Systems
Ch 06: Centripetal Forces & Gravitation
Ch 07: Work & Energy
Ch 08: Conservation of Energy
Ch 09: Momentum & Impulse
Ch 10: Rotational Kinematics
Ch 11: Rotational Inertia & Energy
Ch 12: Torque & Rotational Dynamics
Ch 13: Rotational Equilibrium
Ch 14: Angular Momentum
Ch 15: Periodic Motion (NEW)
Ch 15: Periodic Motion (Oscillations)
Ch 16: Waves & Sound
Ch 17: Fluid Mechanics
Ch 18: Heat and Temperature
Ch 19: Kinetic Theory of Ideal Gasses
Ch 20: The First Law of Thermodynamics
Ch 21: The Second Law of Thermodynamics
Ch 22: Electric Force & Field; Gauss' Law
Ch 23: Electric Potential
Ch 24: Capacitors & Dielectrics
Ch 25: Resistors & DC Circuits
Ch 26: Magnetic Fields and Forces
Ch 27: Sources of Magnetic Field
Ch 28: Induction and Inductance
Ch 29: Alternating Current
Ch 30: Electromagnetic Waves
Ch 31: Geometric Optics
Ch 32: Wave Optics
Ch 34: Special Relativity
Ch 35: Particle-Wave Duality
Ch 36: Atomic Structure
Ch 37: Nuclear Physics
Ch 38: Quantum Mechanics

Concept #1: Power in Circuits

Practice: A hair dryer operates at 120 V (the voltage produced by a household outlet), and outputs 1200 W of energy. For this problem, treat the hair dryer as a single resistor. 

(a) At what current does the hair dryer operate?
(b) What is the resistance of the hair dryer?

Practice: An incandescent lightbulb produces 100 W of light. If this lightbulb operates at 25% efficiency (meaning that out of all the power it generates, only 25% is released as light), what resistance must the lightbulb have if it operates at 120 V?

Additional Problems
A 200-W light bulb is connected across 110 V. What current will flow through this bulb? A) 0.9 A B) 0 A C) 0.6 A D) 1.8 A
Which bulb will be the brightest if connected in series? The voltages and wattages shown in the graphs are their nominal settings, not actual values when connected in series. A) 60 W bulb B) 120 W bulb C) 240 W bulb D) Equally bright
Four identical resistors are connected in series to an ideal battery. The total power supplied by the battery is 10 W. The same resistors are then connected to the same battery in parallel. What is the total power supplied by the battery in this new, parallel configuration? A) 0.6 W B) 2.5 W C) 40 W D) 160 W E) It is impossible to say with the given information.
For most materials, the resistance is actually temperature dependent, and typically increases as temperature rises. For this problem, however, let's assume a very simple (if not physical) case. A 100 Ω resistor with a mass of 0.15 kg is connected to a 120 V power source. So long as the temperature is below 1000°C, the resistance remains 100 Ω, but once it rises above 1000°C, the resistance immediately becomes infinite, and the circuit can no longer operate. How long could this circuit run? The specific heat of the resistor we are considering is 50 J/g*K and we will assume the resistor begins at room temperature, about 23°C.
A car's battery produces 12 V and has a charge of 70 A*hr. How long could the battery run a car whose entire electronic system had an equivalent resistance of 5 Ω? This assumes that the alternator isn't recharging the battery as you drive.
The resistivity of gold is 2.44 x 10 -8 Ω•m at a temperature of 20°C. A gold wire, 1.8 mm in diameter and 14 cm long, carries a current of 480 ma. The power dissipated in the wire is closest to: A) 0.077 mW B) 0.25 mW C) 0.14 mW D) 0.19 mW E) 0.31 mW
The resistivity of gold is 2.44 x 10 -8 Ω•m at a temperature of 20°C. A gold wire, 1.4 mm in diameter and 17 cm long, carries a current of 190 ma. The power dissipated in the wire is closest to: A) 0.043 mW B) 0.079 mW C) 0.061 mW D) 0.024 mW E) 0.097 mW
A 1500 W hair dyer is designed to be used with an electrical outlet that provides 115 V. What current does the hair dryer draw from the outlet? a. 0.8 A b. 13 A c. 3.6 A d. 12 A