A moving charge creates a magnetic field as well as an electric field.
SET UP: The magnetic field caused by a moving charge is B = 0
, and its electric field is E =
4 r 2
4 P r 2
since q = e.
EXECUTE: Substitute the appropria
MAGNETIC FIELD AND MAGNETIC FORCES
IDENTIFY and SET UP: Apply Eq.(27.2) to calculate F . Use the cross products of unit vectors from Section 1.10.
EXECUTE: v = ( +4.19 104 m/s ) i + ( 3.85 104 m/s ) j
(a) B = (1.40 T ) i
F = qv B = ( 1
IDENTIFY: An uncharged capacitor is placed into a circuit. Apply the loop rule at each time.
SET UP: The voltage across a capacitor is VC = q / C .
EXECUTE: (a) At the instant the circuit is completed, there is no voltage
CURRENT, RESISTANCE, AND ELECTROMOTIVE FORCE
I = Q / t . Use I = n q vd A to calculate the drift velocity vd .
n = 5.8 1028 m 3 .
(a) I =
q = 1.60 1019 C .
= 8.75 102 A.
(b) I = n q vd A. This gives vd
CAPACITANCE AND DIELECTRICS
IDENTIFY: For capacitors in parallel the voltages are the same and the charges add. For capacitors in series, the
charges are the same and the voltages add. C = Q / V .
SET UP: C1 and C2 are in parallel and C3 is in s
Physics 9C-A Homework Assignment#7 (due on 2/23/10)
Optional (for 2 extra points and fun): In Example 24.7, let the total resistance of
the wires that connect the two capacitors be R. Shown that the loss of the store