ECEN 1400 - Introduction to Digital and Analog Electronics

Peter Mathys, Spring 2014

Problems for Wed. 01-22-14

Problem 2.1 A laptop computer is powered by a power supply that delivers 4.5 A at 16 V. The efficiency of the power supply is 85%.

(a) If the computer is turned on at all times, how many kilowatt-hours does the power supply use in 24 hours?

(b) If the price per kWh is 12 cents, how much does it cost to run the computer continuously for one week?

Problem 2.2 Consider the following circuit.

Circuit for Problem 2.2

(a) Compute the power absorbed by each of the resistors. Hint: Compute the equivalent resistance for the combination of the 150 and 820 ohm resistors first. Then you can compute the total current delivered by the power supply and the voltage across the 150 and 820 ohm resistors.

(b) If you only have 0.25 W resistors with standard values (100, 120,150, 180, 220, 270, 330, 390, 470, 560, 680, 820, 1.0k, 1.2k, 1.5k, 1.8k, 2.2k, 2.7k, 3.3k, 3.9k, 4.7k, 5.6k, 6.8k, 8.2k, 10k) available, how would you modify the circuit so that no resistor burns up and the resistances in the given circuit remain within 5% of their labeled values?