Seed = 3324. (If you are not the instructor, you can ignore the seed.) **** SOLUTION(S) ****
Problem 1. The smallest unit of a compound is:
a) an electron
b) an element
c) a neutron
d) a molecule
The correct answer is d) a molecule
Problem 2. Describe the difference between a chemically inert element and a semiconductor, in terms of their valence electrons.
Chemically inert elements have full valence shells, semiconductors have half their valence shell filleed (4 valence electrons).
Problem 3. True/False: Electric potential and voltage are the same thing.
The correct answer is a) False
False. Voltage is potential *difference*.
Problem 4. Describe the difference between "conventional" current and "physical" current.
Conventional current involves the flow of imaginary positive particles, physical current is the flow of electrons.
Problem 5. Prefixes:
a. A current of 210 μA refers to how many Amperes?
b. 13.2 kV is how many Volts?
c. 18.7 MΩ is how many Ohms?
d. Express 13.2 V in units of mV.
a. 210 μA = 0.00021 A
b. 13.2 kV = 1.32e+04 V
c. 18.7 MΩ = 1.87e+07 Ω
d. 13.2 V = 13200 mV
Problem 6. A dielectric with a positive charge of 2.31 C has 2.63e+18 electrons added to it. What is the (new) net charge of the dielectric in Coulombs?
a) 1.89 C
b) 3 C
c) 2.73 C
d) 1.72 C
e) None of these
The correct answer is a) 1.89 C
Problem 7. A charge of 8.98 mC flows through a particular guitar cable in 726 seconds.
a. What is the current that flows?
b. Approximately how many electrons pass?
c. If one finds a potential difference of 7.9 V across the wire, what is its resistance?
a. I = Q/t = (0.00898 C) / (726 s) = 1.24e-05 A = 12.4 μA
b. (0.00898 C) / (1.602e-19 C / electron) = 5.61e+16 electrons
c. R = V / I = (7.9 V) / (1.24e-05 A) = 6.37e+05 Ω
Problem 8. A resistor has blue, red, and green for its first three color bands.
What is the value of the resistor?
a) 6.2 MΩ
b) 0.51 MΩ
c) 62 MΩ
d) None of these
e) 5.1 MΩ
The correct answer is a) 6.2 MΩ
Problem 9. Yes/No: In a short circuit, does current flow?
The correct answer is b) Yes
Problem 10. A voltage of 12 V exists across a 36.2 Ω resistor. How much charge flows through it in 16.4 seconds?
I = V/R = Q/t.
Thus Q = t V / R = (16.4 s)(12 V)/(36.2 Ω) = 5.44 C
Problem 11. The amount of useful output power provided by a device is 2.1 W. It is powered by a 48 V supply with 216 mA of current. How much power is wasted in heat?
a) 5.96 W
b) None of these
c) 8.3 W
d) 12.5 W
e) 10400 W
The correct answer is c) 8.3 W
Problem 12. Two resistors, RA and RB, are placed in series. If RA > RB and a voltage is applied across this resistor combination, which resistor will dissipate more power?
b) They will dissipate the same amount of power
c) Impossible to determine; need more information to answer
The correct answer is d) RA
Problem 13. Two resistors, R1 = 151 Ω and R2 = 630 Ω, are placed in series across a 7.07 V supply.
a. What is the current through the smaller resistor?
b. Through the larger resistor?
a. The total resistance is RT = R1 + R2 = 781 Ω.
Thus I = V / RT = (7.07 V) / (781 Ω) = 0.00905 A = 9.05 mA
b. Since they are in series, the current is the same for both resistors.