Physics Final Unit 2
The units of capacitance are equivalent to (show your unit check):
(C^2)/J
Copper contains 8.4 x 10^28 free electrons per cubic meter. A copper wire of cross-sectional area of 7.4 x 10^-7 m^2 carries a current of 1 A. The electron drift speed is approximately:
10^-4 m/s
In the diagram, the current in the (in series and its a 3 ohm and 2 ohm) resistor is 4 A. The potential difference between points 1 and 2 is:
20 V
A charged capacitor stores 10 C at 40 V. Its stored energy is:
200 J
Four 20-ohm resistors are connected in series and the combination is connected to a 20-V emf device. The potential difference across any one of the resistors is:
5 V
A 10-ohm resistor has a constant current. If 1200 C of charge flow through it in 4 minutes what is the value of the current?
5.0 A
A parallel-plate capacitor has a plate area of 0.2 m^2 and a plate separation of 0.1 mm. To obtain an electric field of 2.0 x 10^6 V/m between the plates, the magnitude of the charge on each plate should be:
7.1 x 10^-6 C
In the diagram(In series) R1 > R2 > R3. Rank the the three resistors according to the current in them, from least to greatest
All are the same
A farad is the same as a:
C/V
"The sum of the currents into a junction equals the sum of the currents out of the junction" is a consequence of:
Conservation of charge
"The sum of the emf's and potential differences around a closed loop equals zero" is a consequence of:
Conservation of energy
Derive the expression for equivalent capacitance for capacitors in series, completely and clearly
Derive the expression for equivalent resistance for resistors in series, completely and clearly
If the space between the plates of a capacitor is filled with a dielectric material, the capacitance C is decreased by a factor k , called the dielectric constant.
False
The average drift speed of electrons moving in a wire when the wire is hooked up to a voltage source such as a car battery is very close to the speed of light.
False
The equivalent capacitance of resistors in series is always less than any of the resistors making up the series in network.
False
Resistance is the property of a(n) ______object/material ______. Resistivity is the property of a(n) ______object/material______.
Object Material
Complete and clearly indicate the physical significance of the temperature coefficient of resistivity (in words as well as symbolically) beginning with the temperature dependent equation for resistivity.
P = P0[1 + a(T-T0)] a = resistance a = ((P - aP0)/P0)/(T - T0) ------------------------------------------------- a = fractional change per change in Temp fractional change = (P - P0)/P0 change in Temp = T - T0
A battery is used to charge a series combination of two identical capacitors. If the potential difference across the battery terminals is V and total charge Q flows through the battery during the charging process then the charge on the positive plate of each capacitor and the potential difference across each capacitor are:
Q and V/2, respectively
A Capacitor C "has a charge of Q". The actual charges on its plates are:
Q, -Q
How does the capacitance of two identical capacitors connected in series compare to that of one of the capacitors?
The two capacitors connected in series have a smaller capacitance
Which of the following graphs best represents the current-voltage relationship for a device that obeys Ohm's law?
Think of V=i*r ---> 1 x 1 relationship
The capacitance of a system depends only on the geometry of the conductors.
True
The equivalent capacitance of capacitors in series is always less than any of capacitors making up the series network.
True
The time constant for a charging RC-circuit is the time needed for the current in the circuit to reach 63% of its maximum value.
True
Current is a measure of:
amount of charge that moves past a point per unit time
A car battery is rated at 80 A * h. An ampere-hour is a unit of:
charge
Current has units:
coulomb/second
For an ohmic resistor, resistance is the proportionality constant for:
current and potential difference.
The capacitance of a parallel-plate capacitor can be increased by:
decreasing the plate separation
Which process doubles the power given off by a resistor?
doubling the current by making a resistance half as big
At which location will the electric field between the two parallel plates of a charged capacitor be the strongest in magnitude?
electric field is constant throughout space between plates
Derive the general expression for equivalent capacitance for capacitors in series, completely and clearly.
eq = equivalence For Capacitors in series, Charge is the same Q1 = Q2 = Q3 = Qeq For Capacitors, Potential Sum V = V1 + V2 + V3 = Veq Series: (Qeq/Ceq) = (Q1/C1) + (Q2/C2) + (Q3/C3) (1/Qeq)(Qeq/Ceq) = [(Q1/C1) + (Q2/C2) + (Q3/C3)](1/Qeq) (1/Ceq) = (1/C1) + (1/C2) + (1/C3)
This figure shows a junction. What is true of the currents?
i1 = i0 - i2
the units of resistivity are:
ohm*meter
The capacitance of a parallel-plate capacitor is:
proportional to the plate area
Capacitor C1 is connected alone to a battery and charge ob each plate is 4.0 x 10^-8 C. Then it is removed from the batter and connected to two other capacitors C2 and C3, as shown. The charge on the positive plate of C1 is the 1.0 x 10^-8C. The charges on the positive plates of C2 and C3 are:
q2 = 3.0 x 10^-8 C and q3 = 3.0 x 10^-8 C
A battery is used to charge a parallel-plate capacitor, after which it is disconnected. Then the plates are pulled apart to twice their original separation. This process will double the:
stored energy
Conduction electrons move to the right in a certain wire. This indicates that:
the current density and electric field both point left
If the potential difference across a single capacitor is doubled, by what factor does the stored energy in the capacitor change?
the new energy is four times the original
Two wires made of different materials have the same uniform current density. They carry the same current only if:
their cross-sectional areas are the same
In the context of the loop and junctions rules for electrical circuits a junction is:
where three or more wires are joined