Physics Lab 3 Practice Quiz
The dielectric strength of air is 0.8 kV/mm. After rubbing your shoes you discharge by touching a faucet. Arcing occurred over 1 cm. You have delivered a voltage of about 8000. J/c. If your body resistance is 800000 ohms how much current passed through your body to ground? 1000 A 10 A 1 A 10 mA 1 mA
10 mA Response Feedback: Since V = IR then I = V/R Therefore I = 8000 / 800000 = 0.01 A = 10 mA
A 0.60 uF capacitor is initially charged to 118 volts and then connected across the terminals of 600. ohm resistor. What will be the initial current in the resistor the instant after the capacitor is connected. 0.00 mA 197 mA 2.0E2 mA 62 A 197 A
197 mA Response Feedback: Since V = IR. then I = V/R Then I = 118 / 600. = 0.197 A = 197 mA
Find the capacitance of a parallel plate capacitor that has two square plates both having a side length of 6.0 cm, where these plates are separated by 15.0 mm. Assume the insulating material between the two plates is a vacuum. (?0= 8.85E-12 C^2/Nm^2; k = 1 for vacuum). 2.124 E-12 2.1 E-12 6.7 E-12 6.672 E-12
2.1 E-12
Given e represents the base of the natural logarithm (Naperian base). To four decimal places what is the value of e? Hint: use your calculator. 2.7183 3.1416 0.3679 2.700 2.7183E4 You made an error in decimal place-value.
2.7183
A 0.60 uF capacitor is initially charged to 134 volts and then connected across the terminals of 600.0 ohm resistor. How much charge is stored by the capacitor after ONE time constant has elapsed. Hint: u stands for micro. 29.6 uC 50.4 uC 36.7 uC 52.6 uC 29.6 C
29.6 uC Answer Feedback: Since Q = Qo*e^(-t/RC) and Qo = VC and t/RC = 1 Then Q = 134*0.60E-06*(e^-1) = 29.6E-06 C = 29.6 uC
Given an initial voltage Vo = 100. volts what is 1/e times that value? 63.2 volts 36.8 volts 63 volts 37 volts 271.83
36.8 volts
A 0.60 uF capacitor is initially charged to 100 volts and then connected across the terminals of 600. ohm resistor. What is the capacitive time constant of the circuit? Hint: u stands for micro; uF means microfarad. 60 seconds 60 us 360 us .360 us e seconds
360 us
A 0.60 uF capacitor is initially charged to 124 volts and then connected across the terminals of 600. ohm resistor. At the end of one time constant what will be the voltage of the capacitor? 88.3 volts 78.4 volts 45.6 volts 41.7 volts 0.00 volts
45.6 volts
One possible way to measure capacitive time constants is to discharge a capacitor through a resistance and measure the time it takes to decrease to 1/e times its initial voltage. If a capacitor is initially charged to 147 volts what will be the voltage after ONE time constant? 92.9 54.1 47.6 99.4 147*e volts
54.1 Response Feedback: Since V = Vo * e^ (-t/RC) and (t/RC) = 1 then V = 147*(2.718^-1) = 54.1 V
Given an initial voltage Vo = 100. volts what is Vo - ( Vo * 1/e )? Note: the value 1 is considered an exact value 63.2 volts 36.8 volts 100 volts infinity Undefined
63.2 volts Response Feedback: Vo - (Vo * 1/e) = 100. - (100 * 1 /2.718) = 63.2 V
A parallel plate capacitor is made up of two circular plates with a 10.0 cm diameter separated by 0.50 mm. If a potential difference of 6.0 V is applied across the capacitor, what is the charge on each plate? (e = 8.55E-12 C^2/Nm^2) 7.8E-10 C 8.06E-10 C 1.3E-10 F 8.1E-10 C 8.1E-10 F
8.1E-10 C
A 0.60 uF capacitor is initially charged to 134 volts and then connected across the terminals of 600.0 ohm resistor. How much charge is stored by the capacitor before being connected across the terminals of the 600.0 ohm resistor? Hint: u stands for micro. 80. uC 13.4 C 80.40 uC 16.7 A 80. C
80. uC Answer Feedback: Since V = Q / C, then Q = VC So Q = 0.00000060*134 = 0.00008 C = 80. uC
The accepted value of the dielectric strength of dry air is about 0.8 kV/mm. If after rubbing your shoes on a wool carpet you touch a metal doorknob and observe arcing over a distance of one centimeter, how many volts of electric potential did you produce? 0.8 V 8.0 V 80 mV 800 mV 8000 V
8000 V Response Feedback: Since dielectric strength of dry air = 0.8 kilovolts/mm = 800 V/mm and 1 centimeter is 10 millimeters, then there was 10*800 = 8000V of electric potential.
If the capacitance in an RC circuit is doubled, the half-life is ______. Reduced by half Doubled Quadrupled Reduced by 1/4
Doubled
If the resistance in an RC circuit is doubled, the half-life is ______. Reduced by 1/4 Reduced by 1/2 Doubled Quadrupled
Doubled Response Feedback: The half life is given by t½ = RC ln 2. Since half life is directly proportional to R, doubling R will double the half life from its original value.
The unit of capacitance is the Faraday Coulomb per Volt Farad Coulomb per second Weber
Farad
When a capacitor discharges, instantaneous current is a function of time according to the expression I(t) = Imax times e raised to the -t/RC power I(t) = Imax times 1/e raised to the -t/RC power I(t) = Imax times e raised to the t/RC power I(t) = Imax times e raised to the RC/t power I(t) = Imax times 1/e raised to the RC power
I(t) = Imax times e raised to the -t/RC power
When a capacitor discharges, its plate charge is a function of time according to the expression Q(t) = Qmax times e raised to the -t/RC power Q(t) = Qmax times 1/e raised to the -t/RC power Q(t) = Qmax times e raised to the t/RC power Q(t) = Qmax times e raised to the RC/t power Q(t) = Qmax times 1/e raised to the RC power
Q(t) = Qmax times e raised to the -t/RC power
The product RC is called the capacitive time constant and has the units of_________. Seconds Coulombs Voltage Hertz
Seconds
A capacitor with a great dielectric constant will have a better ability to store electric charge than a capacitor with a small dielectric constant True False
True
A capacitor with a small dielectric constant will have a lesser ability to store electric charge than a capacitor with a great dielectric constant True False
True
The actual net charge on the capacitor is zero. True False
True
When a capacitor discharges, its instantaneous voltage is a function of time according to the expression V(t) = Vmax times e raised to the -t/RC power V(t) = Vmax times 1/e raised to the -t/RC power V(t) = Vmax times e raised to the t/RC power V(t) = Vmax times e raised to the RC/t power V(t) = Vmax times 1/e raised to the RC/t power
V(t) = Vmax times e raised to the -t/RC power Response Feedback: When a capacitor discharges, its instantaneous voltage is a function of time according to the expression: V (t) = Vmax times e raised to the -t/RC power
When a charged capacitor is disconnected from a battery and connected across a resistor the current will eventually become equal to RC become equal to Imax become negligible compared to initial current increase at a constant rate decrease at a constant rate
become negligible compared to initial current Response Feedback: The current will eventually become negligible compared to initial current.
When a charged capacitor is disconnected from a battery and connected across a resistor the voltage across the capacitor will eventually become equal to RC become equal to Vmax increase at a constant rate decrease at a constant rate become negligible compared to initial voltage
become negligible compared to initial voltage
A capacitor is used to store _________. current voltage charge all of the above
charge
Q is the charge stored in the capacitor; V is the potential difference between the capacitor plates and C the value of the capacitance. These quantities are _______. completely independent from each other characteristics of the capacitor connected by the equation Q = V/C connected by the equation Q = C/V connected by the equation V = Q/C connected by the equation C = V/Q
connected by the equation V = Q/C
The charge stored on the capacitor is _____ to the potential difference between the capacitor plates and _____ to the value of the capacitance. Inversely proportional .. directly proportional directly proportional .. directly proportional Inversely proportional.. inversely proportional Directly proportional .. equal Directly proportional .. inversely proportional
directly proportional .. directly proportional
The potential difference between the capacitor plates is _____ to the plate's charge and _____ to the value of the capacitance inversely proportional .. directly proportional directly proportional .. directly proportional inversely proportional.. inversely proportional directly proportional .. equal directly proportional .. inversely proportional
directly proportional .. inversely proportional
Operationally (in terms of measurements) capacitance of the parallel plate capacitor is inversely proportional to the area and directly proportional to the distance between the plates directly proportional to the area and inversely proportional to the distance between the plates independent of the plate area and the distance between the plates characteristic of a conducting material proportional to resistivity of the plates' material
directly proportional to the area and inversely proportional to the distance between the plates
Capacitance is defined as the ratio of (...). This definition is acceptable when this ratio is constant. work to electric charge work to time electric potential to electric charge electric charge to electric potential electric charge to time
electric charge to electric potential
In your lab you were introduced to capacitive time constant (Tau = RC) in a RC circuit. The theoretical value of the capacitive time constant during charging is _____ the theoretical value of the capacitive time constant during discharging while their experimental values are _____. equal to RC which is also equal to .. approximately equal within experimental error larger than .. equal to each other smaller than .. equal to each other larger than .. approximately equal within experimental error smaller than .. approximately equal within experimental error
equal to RC which is also equal to .. approximately equal within experimental error
A capacitor is connected across a battery and there is no current in the circuit. Then each capacitor plate carries a charge of ____ magnitude and ____ sign as the other one. greater, same less, opposite half the, same equal, opposite equal, the same
equal, opposite Response Feedback: Capacitors work by building up equal and opposite charges on each plate until there is enough charge to overcome the resistance between the plates. Until a capacitor discharges, the charges on the plates remain equal and opposite.
The capacitance of a precisely constructed capacitor depends upon the nature of the substance between the plates (called dielectric) and certain geometric qualities. Capacitance is directly proportional to the distance between the plates and inversely proportional to the area of the plates directly proportional to the distance between the plates and directly proportional to the area of the plates inversely proportional to the distance between the plates and inversely proportional to the area of the plates inversely proportional to the distance between the plates and directly proportional to the area of the plates independent of the filling material between plates
inversely proportional to the distance between the plates and directly proportional to the area of the plates
A capacitor with a dielectric constant equal to zero stores charge easily is shorted out requires a large electric potential difference between the plates does not conduct a direct current is filled with an isolator
is shorted out
When an uncharged capacitor is connected to a battery and connected across a resistor, the graph of the instantaneous current as a function of time asymptotically approaches the vertical axis (current axis) the horizontal axis (time axis) the line I(t) = Imax the line V(t) = Vmax the line Q(t) = Qmax
the horizontal axis (time axis) Answer Feedback: Instantaneous current as a function of time asymptotically approaches the horizontal axis (time axis).
When a charged capacitor is disconnected from a battery and connected across a resistor, the graph of the instantaneous current as a function of time asymptotically approaches the vertical axis (current axis) the horizontal axis (time axis) the line I(t) = Imax the line V(t) = Vmax the line Q(t) = Qmax
the horizontal axis (time axis) Response Feedback: Instantaneous current as a function of time asymptotically approaches the horizontal axis (time axis), because when a charged capacitor is connected across a resistor the voltage drop across the capacitor exponentially decreases. Therefore, current also decreases.
When an initially uncharged capacitor is charged by a storage battery through a resistance connected in series with the capacitor, the graph of the instantaneous voltage as a function of time is asymptotic with respect to the vertical axis the horizontal axis the line I(t) = Imax the line V(t) = Vmax the line Q(t) = Qmax
the line V(t) = Vmax Response Feedback: The graph of the instantaneous voltage as a function of time is asymptotic with respect to the line V (t) = Vmax.
In your lab, you determined the experimental value of the half life. It was obtained by measuring the ___. time dependence of voltage time dependence of charge passing through active resistance time dependence of charge stored by the capacitor time dependence of current passing through the active resistance theoretical value of RC
time dependence of voltage Response Feedback: It was obtained by measuring the time it took for the voltage to decay from X Volts to X/2 Volts from a Voltage vs. time graph.
The half-life, t1/2 is defined to be the time that it takes for the voltage to decrease by half: V (t½) = V0 /2 = V0 * e-(t½/RC). Solving for the half-life gives t½ = RC t½ = RC ln 2 t½ = - RC ln 2 t½ = RC ln 1/2
t½ = RC ln 2
