Download Recitation 4.6 Review

EF152 – Physics for Engineers
Summer, 2012
Recitation 4.6 Review
1. Three point charges are arranged along the x axis. Charge q1=+3.00μC is at the origin, and charge
q2= (-5.00) μC is at x=0.20m. Charge q3= (-8.00) μC. Where is charge q3 located if the net force on q1
is 7.00N in the (-x) direction?
[-0.144 m]
2. A proton is placed in a uniform electric field of 2.75x103 N/C. Calculate:
a. The magnitude of the electric force felt by the proton.
b. The proton’s acceleration
c. The proton’s speed and position after 1.00 μs in the field, assuming it starts form rest.
[a. 4.41x10-16 N; b. 2.63x1011 m/s2; c. 2.63x105 m/s, 0.132m]
3.
A small particle has a charge of (-5.00) μC and a mass of 2.00x10-4 kg. It moves from point A, where
the electric potential is VA=+200V, to point B where the electric potential is VB=+800V. The electric
force is the only force acting on the particle. The particle has a speed of 5.00m/s at point A. What is
its speed at point B?
[7.42 m/s]
4. In the figure to the right, C1=6.00μF, C2=3.00μF, C3=5.00μF. After
the charges on the capacitors have reached their final values, the
charge on C2 is 40.00μC.
a. What are the charges on capacitors C1 and C3?
b. What is the applied voltage Vab?
[a. Q1=80μC, Q3=120μC; b. 37.3 V]
5. In household wiring, 12 gauge copper wire (2.05 mm diameter)
is often used. Find the resistance of a 24.0 m (78.7 ft) length of this wire.
[0.125Ω]
6. Each resistor in the circuit represents a light bulb with a resistance of
4.5Ω. The voltage source is 9.0V. Which bulb or bulbs glows the
brightest?
[P1=10.1 W]
Now bulb R4 is removed from the circuit. Does bulb 1 glow
brighter or duller with R4 removed?
[P1=8.0 W]
7. Two hikers are reading a compass under an overhead transmission line that is 5.50 m above the
ground and carries a current of 800 A in a horizontal direction from north to south. Find the
magnetic field at a point on the ground directly underneath the conductor. Considering that the
magnitude of the earth’s field is on the order of 0.5x10-4 T, is the current really a problem?
[B=2.91x10-5T]
EF152 – Physics for Engineers
Constants
Summer, 2012
Capacitance
me=9.109x10
-31
kg
mp=1.673x10
-27
kg
R-C circuit time constant
Magnetism
Capacitance – parallel plates
-27
mn=1.675x10 kg
k = 9x10
9
ε0 = 8.854 ·10
Capacitance – energy storage
Magnetic force on
moving charged particle
Capacitors in series
Magnetic field of a
moving charged particle
-12
e = -1.6022 ·10
-19
C (electron charge)
-19
J (electron volt)
eV = 1.6022·10
Coulomb’s Law (electrostatic force)
Capacitors in parallel
Magnetic Field of
a straight wire
Resistors in series
Electric Field – point charge
- unit vector from charge to a location
Magnetic field outside two
parallel conductors with
current in opposite directions
Resistors in parallel
Current
Potential energy - point charges
Voltage, Resistance,
Current, Power
Potential
V=I·R
P=I·V
d – distance from the center line of the
wire pair to the axis of one wire.
x – distance from the center line of the
wire pair to the point of interest.
I – current in the wires
Magnetic field along the axis
of a looped wire
Resistance
Potential of a set
of point charges
Kirchhoff’s Rules
Potential difference
between two parallel plates
for a closed loop
for a junction
a – radius of the loop
x – distance from the center of the loop
to point of interest on the axis.
I – current in the wires
N – number of loops