Download Two wires made of the same material have the same lengths

Phys102
Term:123
Online HW-Ch27-Lec02
Q1:
Two wires made of the same material have the same lengths but different diameters.
They are connected in parallel to a battery. The quantity that is NOT the same for
the wires is:
A. the end-to-end potential difference
B. none of the other answers
C. the current
D. the current density
E. the electron drift velocity
Ans:
C
Q2:
A R 1 = 3.00 Ohm and a R 2 = 1.50 Ohm resistor are wired in parallel and the
combination is wired in series to a R 3 = 4.00 Ohm resistor and a 10.0 V emf device .
The potential difference across the R 1 resistor is:
R1
R3
Ans:
�irst �ind total current in the circuit:
R2
ε
ε − iR 3 − iR12 = 0
ε − iR 3 − i
i=
R1 R 2
=0
R1 + R 2
ε
R R2
R 3 + R 1+ R
1
2
Potential across R1 is the same as it is across R 2 or the combination
So V = i
R1 R 2
R1 + R 2
KFUPM-Physics Department
1
Phys102
Term:123
V=
V=
Online HW-Ch27-Lec02
ε
R1 R 2
×
R R
R1 + R 2
R3 + 1 2
R1 + R 2
10
3 × 1.5
×
= 2.00 V
3 × 1.5
3 + 1.5
4+
3 + 1.5
Q3
Switch S, in the figure below is closed at time t = 0 s, to begin charging an
initially uncharged capacitor of capacitance C = 20.0 µF. The capacitor is
connected in series with a resistor of resistance = 30 Ω. At what time is the
potential difference across capacitor is equal to that of resistors?
S
30 V
Ans:
R2
C
Ve−t/RC = V(1 − e−t/RC )
e−t/RC = 1 − e−t/RC
2e−t/RC = 1
−
t
1
= ln � �
RC
2
t = RCln(2) = 30 × 20 × 10−6 × ln(2) = 4.16 × 10−4 S
KFUPM-Physics Department
2