School of Chemistry & Physics, University of KwaZulu-Natal, Pietermaritzburg Campus
PHYS120: DC circuits
F2 Each of the three resistors in the figure has a resistance
of 2 Ω and can dissipate a maximum of 18 W without becoming excessively heated. What maximum power can the
circuit dissipate?
2Ω
2Ω
2Ω
School of Chemistry & Physics, University of KwaZulu-Natal, Pietermaritzburg Campus
PHYS120: DC circuits
F3 A dry cell having an emf of 1.55 V and an internal resistance of 0.08 Ω supplies current to
a 2.0 Ω resistor.
(a) Determine the current in the circuit.
(b) Calculate the terminal voltage of the cell.
School of Chemistry & Physics, University of KwaZulu-Natal, Pietermaritzburg Campus
PHYS120: DC circuits
F4
(a) Find the potential difference Vad in the circuit
(b) Find the potential difference across the 4 V cell
(c) A battery of emf 17 V and internal resistance 1 Ω is
inserted in the circuit at d with its positive terminal
connected to the positive terminal of the 8 V battery.
Find Vbc between the terminals of the 4 V battery.
4 V 0.5 Ω
c
b
b
9Ω
b
b
6Ω
0.5 Ω 8 V
8Ω
a
b
d
School of Chemistry & Physics, University of KwaZulu-Natal, Pietermaritzburg Campus
PHYS120: DC circuits
F5 How many cells, each having an emf of 1.5 V and an internal resistance of 0.50 Ω must be
connected in series to supply a current of 5/3 A to operate an instrument having a resistance
of 6 Ω?
School of Chemistry & Physics, University of KwaZulu-Natal, Pietermaritzburg Campus
PHYS120: DC circuits
F6 A battery has an internal resistance of 0.50 Ω. A number of identical light bulbs, each with
a resistance of 15 Ω, are connected in parallel across the battery terminals. The terminal
voltage of the battery is observed to be half the emf of the battery. How many bulbs are
connected?
School of Chemistry & Physics, University of KwaZulu-Natal, Pietermaritzburg Campus
PHYS120: DC circuits
F7 A galvanometer has a full-scale reading of 100 µA and a coil resistance of Rc = 50.0 Ω.
Determine the resistance that must be connected
(a) in series with the coil to produce a voltmeter that will register a full-scale reading of
0.500 V.
(b) in parallel with the coil to produce an ammeter that will register a full-scale reading
of 60.0 mA.
School of Chemistry & Physics, University of KwaZulu-Natal, Pietermaritzburg Campus
PHYS120: DC circuits
1Ω
F8 Find the magnitude and direction of the current in the 2.0 Ω resistor in the diagram opposite.
2Ω
a
1V
b
b
3Ω
4V
b
School of Chemistry & Physics, University of KwaZulu-Natal, Pietermaritzburg Campus
PHYS120: DC circuits
5Ω
F9 Determine the voltage across the 5.0 Ω resistor
in the circuit opposite. Which end of the resistor
is at the higher potential?
10 Ω
a
b
10 Ω
10 V
15 V
2V
School of Chemistry & Physics, University of KwaZulu-Natal, Pietermaritzburg Campus
PHYS120: DC circuits
F10 Determine the current through each of the
resistors in the figure opposite.
15 Ω
30 Ω
10 Ω
6V
25 Ω
20 Ω
School of Chemistry & Physics, University of KwaZulu-Natal, Pietermaritzburg Campus
PHYS120: DC circuits
F12 Consider a series RC circuit for which C = 6 µF, R = 2 × 106 Ω and E = 20 V. Find (a) the
time constant of the circuit, (b) the maximum charge on the capacitor after a switch in the
circuit is closed, and (c) the current in the circuit at the instant just after the switch in the
circuit is closed.
School of Chemistry & Physics, University of KwaZulu-Natal, Pietermaritzburg Campus
PHYS120: DC circuits
F13 A 2 nF capacitor with an initial charge of 5.1 µC is discharged through a 1300 Ω resistor.
Calculate (a) the maximum current through the resistor, (b) the current through the resistor
9.0 µs after the resistor is connected across the terminals of the capacitor, and (c) the charge
remaining on the capacitor after 8.0 µs.
School of Chemistry & Physics, University of KwaZulu-Natal, Pietermaritzburg Campus
PHYS120: DC circuits
F14 How many time constants must lapse before a capacitor in a series RC circuit is charged to
within 0.1 % of its equilibrium charge?
School of Chemistry & Physics, University of KwaZulu-Natal, Pietermaritzburg Campus
PHYS120: DC circuits
F15 An electronic flash attachment for a camera produces a flash by using the energy stored
in a 750 µF capacitor. Between flashes, the capacitor recharges through a resistor whose
resistance is chosen so that the capacitor will recharge with a time constant of 3 s. Determine
the value of the resistance.
School of Chemistry & Physics, University of KwaZulu-Natal, Pietermaritzburg Campus
PHYS120: DC circuits
F16 Three identical capacitors are connected with a resistor in two different ways. When they
are connected as in Figure (a), the time constant is 20 ms. What is the time constant when
they are connected with the same resistor as in Figure (b)?
C
C
C
C
(a)
C
R
(b)
C
R