ENGR 2613 – Electrical Science
Chapter 2: Basic Components and Electric Circuits
Homework #1 – Due 6/2/15@ beginning of class
Problem #2.1
The electrical power consumed by a resistive heating element is a constant 6 W over the
first 5 minutes, zero for the following 2 minutes, a value that increases linearly from zero
to 10 W during the next 10 minutes.
a.) What is the total energy output in joules during this 17 minute interval?[4.8 kJ]
b.) What is the average power output in W during this time? [4.7 W]
c.) Sketch a plot showing power as a function of time and energy as a function of
time.
Problem #2.2
The energy contained in the BOX (relative to its initial state) is shown in the graph
below.
a.) Graph the voltage of the BOX for 0 < t < 12 s.
b.) Graph the current flowing into the top of the box for 0 < t < 12 s.
c.) Graph the power absorbed by the BOX for 0 < t < 12 s.
Problem #2.3
The total charge accumulated by a certain device is given as a function of time by
q = 18t2 – 2t3 (in base SI units)
a.) What total charge is accumulated at t = 2 s?
b.) What is the maximum charge accumulated in the interval 0 < t < 3 s, and when
does it occur?
c.) At what rate is charge being accumulated at t = 0.8 s?
Use explicit methods (calculus!) to determine your answers.
Problem #2.4
Use Excel to plot q as a function of t and i as a function of t in the interval 0 < t < 3 s
based on the information in Problem #2.3. Show that the values used to plot your
function were calculated in Excel (don’t just copy from a calculations or a graph on your
calculator!). Refer to your syllabus for EXCEL graph guidelines.
Problem #2.5
Determine the power being absorbed by the element if:
a.) V1 = 9 V and I = 2 A
b.) V1 = 9 V and I = -3 A
c.) V1 = -12 V and I = 2 A
d.) V1 = -12 V and I = -3 A
Problem #2.6
Calculate the power being absorbed by element A in the circuit below.
Calculate the power being supplied by element A in the circuit below.
Problem #2.7
Element B supplies 60 W of power. Calculate Ix.
Element B supplies 72 W of power. Calculate VA.
Problem #2.8
a.) Determine the power being absorbed by each element in Fig. 2.32.
b.) Indicate which ones are being charged.
c.) Determine the total average power for the elements that are absorbing positive
power in the circuit.
d.) Determine the total average power for the elements that are supplying positive
power in the circuit.
e.) Show that the net power of the circuit is zero.