Lab 6-3 Practice Exam- Capacitance and RC Circuit

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?

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.

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).

2.1 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

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

Given an initial voltage Vo = 100. volts what is 1/e times that value?

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.

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?

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?

54.1

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

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)

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

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?

8000 V

If the capacitance in an RC circuit is doubled, the half-life is ______.

Doubled

If the resistance in an RC circuit is doubled, the half-life is ______.

Doubled

The unit of capacitance is the

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

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

The product RC is called the capacitive time constant and has the units of_________.

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

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

The actual net charge on the capacitor is zero.

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

When a charged capacitor is disconnected from a battery and connected across a resistor 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 negligible compared to initial voltage

A capacitor is used to store _________.

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 _______.

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.

directly proportional .. directly proportional

The potential difference between the capacitor plates is _____ to the plate's charge and _____ to the value of the capacitance

directly proportional .. inversely proportional

Operationally (in terms of measurements) capacitance of the parallel plate capacitor is

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.

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

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.

equal, 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

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

is shorted out

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 horizontal axis (time axis)

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 horizontal axis (time axis)

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 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

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 ln 2