1a. A capacitor C begins discharging at t = 0 through a resistor R. At what time

Question

1a. A capacitor C begins discharging at t = 0 through a resistor R. At what time has it discharged to 37% of its initial (t=0) charge?

A) R/C
B) RV
C) C/R
D) RC
E) V/R
F) R/V
G) CV
H) V/C

1b. Your car's wiper blades have several settings for the time between when they sweep across your windshield. This timing can be set by an RC circuit. If you were to increase the resistance of the resistor in this circuit, the blades would wipe:

A) more often
B) less often
C) at the same time interval

1c. What quantity is most directly dangerous to the human body?

A) high voltage
B) high current
C) high electric field strength
D) high conductivity
E) high resistance

1d. What's the minimum threshold for often fatal heart fibrillation due to electricity?

A) 120 Volts (AC), 240 Volts (DC)
B) 310 Ohms (AC or DC)
C) 120 Volts (DC), 240 Volts (AC)
D) 15 mc (AC), 60 mA (DC)
E) 310 Ohms (AC), 290 Ohms (DC)
F) 100 mA (AC), 500 mA (DC)

Explanation / Answer

1a)
use
Q = Qo*e^(-t/tau)
0.37Qo = Qo*e^(-t/RC)
0.37 = e^(-t/RC)
-t/RC = -1
t = RC
Answer: D

1b)
Q = Qo*e^(-t/tau)
if R is increased, tau incraeses. SO time taken to discharge increases.
Answer: B

1c)
It is the current that kills
Answer: B

1d)
A) 120 Volts (AC), 240 Volts (DC)
its fact

Related Questions

Navigate

• Browse (All)
• Browse 1
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.