Electrical Engineering in Context Test Bank

Electrical Engineering in Context Test Bank 1 © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.Chapter 1 – Introduction 1.The figure below shows four waveforms labeled (a) to (d). Match the waveform to following signal

type that is most likely:

a.Analog _____ b.Digital _____ c.Analog with noise______ d.Quantized analog ________

ANS:

a.Analog (d) b.Digital (a) c.Analog with noise (b) d.Quantized analog (c) 2.Ten samples of a digital signal that is detected in the presence of noise are given below. The original digital signal values are either equal to -1 or +1. Apply a threshold to the detected samples to form the reconstructed digital data values.

Detected values: 0.8, 0.5, -1.1, -0.4, 1.3, 0.8, -0.7, -0.9, 1.1, -0.8

ANS: Apply a threshold equal to 0, halfway between -1 and +1.

The reconstructed data values: 1, 1, -1, -1, 1, 1, -1, -1, 1, -1

Electrical Engineering in Context Smart Devices, Robots & Communications, 1e Roman Kuc (Test Bank, All Chapters. 100% Original Verified, A+ Grade)

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Electrical Engineering in Context Test Bank 2 © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.Chapter 2 – Sensors and Actuators 1.A scientific calculator has 5 rows and 9 columns. How many bits required for addressing assuming separate row and column addresses?ANS: 5 Rows → 3 bits, 9 columns → 4 bits: 7-bit address required.

2.Your smartphone touch screen implements a 100 x 100 switch array. What is the minimum number of bits that defines the address of each switch assuming separate row and column addresses?ANS: 100 Rows → 7 bits, 100 columns → 7 bits: 14-bit address required.

3.Finger swipe speed. Your smartphone square touch screen measures 10 cm x 10 cm andimplements a 100 x 100 switch array. A horizontal finger swipe must activate at least 25columns in any particular row within 0.5 seconds. What is the minimum speed (m/s) that your finger must travel to form a valid finger swipe?ANS: The finger must travel distance d > a quarter of the horizontal distance in 0.5 seconds. The speed is then s > d/0.5s = (2.5 x 10 -2 m)/(0.5 s) = 5 x 10 -2 m/s.

4.Your audio system uses 24 bits to encode audio waveform samples. How many different levelscan be encoded using the approximation 2 10 = 10 3 ?

ANS: 2

24 = (2 4 )(2 10 )(2 10

) = 16(10

3 )(10 3

• = 16 million

5.Your smartphone has an 8 Megapixel camera (2 23 pixels) with each pixel containing red, green, and blue sensors. If each sensor produces 256 levels of intensity, how many bits are required toencode an image? (Express answer as n.n x 10 y )

ANS: 256 levels are encoded with 8 bits, yielding 24 bits/pixel. 24 x 2

23 = 2.4 x 2 24 =

(2.4)(2

4 )(2 10 )(2 10

) = (2.4)(16)(10

3 )(10 3

• = 3.8 x 10

7 .

6.A consumer TV with 4K resolution has a screen that contains 3840 by 2160 array of pixels. Each RGB LED can shine at 256 intensity levels. The number of bits required to display a complete image equals ______. ? (Express answer as n.n x 10 y )

ANS: (3)(8)(3,840)(2,160) = 199 x10

6 =2.0 x 10

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Electrical Engineering in Context Test Bank 3 © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.

7.An IR autofocus system has emitter and detector apertures separated by 1cm and modeled as pin holes. The light reflected from an object at range r casts a spot that is detected at a displacement of 0.1mm from the detector axis. The detector lies 0.5cm behind the pin hole. The value of r equals _____ (x.x m)

ANS: f = 5x10

-3 m, s = 10 -2 m, x=10 -4

• r/s = f/x → r = sf/x = (10

-2 m)(5 x 10 -3 m)/ (10 -4

• = 5 x

10 -1 m = 0.5 m.

8.An air sonar detects the echo TOF from an object to be 10 milliseconds. The object range equals ___(x.xx) m.

ANS: r = (c)(TOF)/2. In air c=350 m/s. r = (350 m/s) (10

-2 s)/ 2 = 1.75 m 9.An underwater sonar detects the echo from an object at 100m range. The TOF equals ___ ( x.xx s).ANS: TOF = 2r/c. In water c=1500 m/s. TOF = (2 x 100m)/ (1500 m/s) = 0.133 s = 1.33 s 3 / 4

Electrical Engineering in Context Test Bank 4 © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.Chapter 3 – Electric Circuits Section 3.2. Electrical quantities.

• If a charge of 4C flows in 0.25 s through a wire, the current is ___ A.

ANS: I = ΔQ/Δt = 4C/0.25s = 8A.

• A 12V car battery delivers 20A for 15 minutes before it is exhausted. The energy contained in the

battery equals ____ W-hr.

ANS: E = Power x time = V x I x t = 12V x 20A x 0.25 hr = 60 W-hr.

• If a 12V car battery delivers 200A to the starter motor. The power supplied by the battery to the

motor equals____ W.

ANS: P = V x I = 12V x 200A =2400 W.

Section 3.3. Electrical Components.

• A capacitor is modeled as a pair of parallel plates. Its physical size is changed by increasing its length

and width each by a factor of 3 and reducing the separation between the plates by a factor of 4. This changes the capacitance by a factor of ____.

ANS: 8

Analysis: C = εA/d = ε (l x w)/d. ΔC = ΔA/Δd = (Δl x Δw)/Δd = (3 x 3)/0.25 = 36.

• An inductor is modeled as a coil of wire. Its physical size is changed by increasing the coil diameter,

number of turns and its length, each by a factor of 4. This changes the inductance value by a factor of _______.

ANS: L = μN

2

A/L. ΔL = (ΔN)

2

ΔA/ΔL = (4)

2 x (4) 2

/4 =64.

Section 3.3.1. Batteries as Power Sources

• A 9.6V rechargeable Ni-MH battery pack has a rating of 2400 mA-hr and powers a robot for 30

minutes. The average current my robot uses equals ____ A.

ANS: I x T = 2.4 A-hr. I = 2.4 A-hr/0.5 hr = 4.8A.

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