Chapters 27 (021)
Q16 A certain capacitor, in series with a 720-ohm
resistor, is being charged. At the end of 10 milliseconds,
its charge is 50 % of the maximum charge. The
capacitance is:
A1
A2
A3
A4
A5
20 micro-Farad
14 micro-Farad
10 micro-Farad
9.6 micro-Farad
7.2 micro-Farad
Q17 A battery is connected across a series combination
of two identical resistors. If the potential difference
across the terminals of the battery is V, and the current
in the battery is I, then:
A1 the potential difference across
each resistor is V/2 and the current
in each resistor is I.
A2 the potential difference across
each resistor is V/2 and the current
in each resistor is I/2.
A3 the potential difference across
each resistor is V and the current in
each resistor is I/2.
A4 the potential difference across
each resistor is V and the current in
each resistor is I.
A5 the potential difference across
each resistor is V/2 and the current
in each resistor is 2I.
Q18 In figure 5, the current in the 5.0-ohm resistor
is 3.0 A. What is the potential difference Va – Vb?
A1
A2
A3
A4
A5
+ 30 V
- 30 V
+ 6.0 V
- 6.0 V
+ 54 V
Q19 In figure 6: R1 = 2.0 ohms, R2 = 4.0 ohms, R3
= 8.0 ohms, E1 = 2.0 volts, E2 = 4.0 volts and E3 =
6.0 volts. What is the rate of energy dissipation in
R1?
A1
A2
A3
A4
A5
0.32 W
0.08 W
0.16 W
0.24 W
0.40 W
S-28-2
A 9.00 volt battery delivers 117 mA when connected to a 72.0
 load. Determine the internal resistance of the battery.
S-28-9
Two 1.5 volt batteries –with their positive terminals in the same
direction- are inserted in series into the barrel of a flashlight.
One battery has an internal resistance of 0.255  and the other
an internal resistance of 0.153 . When the switch is closed, a
current of 600 mA occurs in the lamp.
a- What is the lamps resistance?
b- What fraction of the power dissipated is dissipated in the
batteries?
S-28-14
Find the equivalent resistor in the circuit shown in the figure.
If Vab is 34 volts, what is the current through each resistor?
S-28-47
The circuit in the figure has been connected for a long time.
a- What is the voltage across the capacitor?
b- If the battery is disconnected, how long does it take the
capacitor to discharge to 1/10 of its initial voltage?
S-28-39
Calculate the power dissipated in each resistor in the figure.
S-28-28
In the circuit of the figure,
a- find the current through each resistor.
b- find the voltage across the 200 W resistor.
S-28-21
Find the potential Vab.
Extra
A capacitor in an RC (R = 2 , C = 5 F) circuit is initially
uncharged. A 9 volt battery is attached in series to the resistor.
How much charge is at the capacitor plate one time constant
after the switch is closed?