DC CIRCUIS EXCEL SOURCE Flashcards
PROBLEMS AND OBJECTIVE TYPE QUESTIONS
If a complex circuit is reduced to an equivalent circuit consisting of a single voltage source in series with a single resistor, this is an example of:
Thevenin`s theorem
Two equal resistors when connected in series across a supply draws a total power of 20 watts. What is the total power drawn when the two resistors are connected in parallel across the same supply?
20 W
Assuming a power source to have a fixed value of internal impedance, maximum power will be transferred to the load when:
The load impedance equals the internal impedance of the source.
Two resistors x and y are connected in parallel. Resistor x having a value of 6 ohms while resistor y being adjustable over a wide range. The parallel combination is then connected through a 2 – ohm line resistor to a 120 V DC source. For what resistance y will its power be the greatest?
1.5 Ω
A load is connected to a network. At terminals to which the load is connected, Rth = 10 Ω and Vth = 40 V. The maximum possible power supplied to the load is:
40 W
An ampere is how many abampere?
0.1
If a complex circuit is reduced to an equivalent circuit consisting of a single current source in parallel with a single resistor, this is an example of:
Norton`s theorem
In any closed loop in a network, the algebraic sum of the voltage drops (i.e. products of current and resistance) taken around the loop is equal to the resultant e.m.f. acting in that loop. This is known as:
Voltage law
In any network made up of linear resistances and containing more than one source of e.m.f., the resultant current flowing in any branch is the algebraic sum of the currents that would flow in that branch if each source was considered separately. What is this theorem?
Superposition theorem
The current in any branch of a network is that which would result if an e.m.f. equal to the p.d. across a break made in the branch, were introduced into the branch, all other e.m.f.’s being removed and represented by the internal resistances of the sources.
Thevenin`s theorem
The power transferred from a supply source to a load is at its maximum when the resistance of the load is _______ the internal resistance of the source.
equal to
The terminal voltage of a battery is 11.8 V when delivering 20W of power to an external load resistor R. If the battery has an emf of 15V, find the internal resistance of the battery.
1.89 Ω
Three series resistors A, B and C are connected across a 120 – V supply. If the resistor A = 50 ohms and the voltage across resistor B = 40V. when the current is ½ A. what is the resistance in resistor C in ohms?
110 Ω
Under the conditions of maximum power transfer, a voltage source is delivering a power of 15 W to the load. What is the power generated by the source?
30 W
What is the efficiency for maximum power transfer?
50%
What is the first step in Norton’s theorem?
Short the load under test
What is the first step in Thevenin’s theorem?
Open the load under test
A conductor whose diameter is 0.175 inch has a resistance of 0.5 ohm. The wire is drawn through a series of dies until its diameter is reduced to 0.08 inch. Assuming the specific resistance of the material remains constant, what is the resistance of the lengthened conductor?
11.45 Ω
In a voltage divider network, the total resistance
Should be as small as the power supply will allow
Two (2) 115-V incandescent lamps A and B are connected in series across a 230-V source. If lamp A is rated at 75 watts and lamp B is rated 50 watts, determine the current by the series connection.
0.52 A
A process equipment contains 100 gallons of water at 25°C. It is required to bring it to boiling point in 10 minutes. The heat loss is estimated to be 5%. What is the kW rating of the heater?
208.47
The resistance of a transformer winding is 0.25 ohm at 25°C. When operating at full load, the temperature of the winding is 75°C. The temperature coefficient of resistance for copper is 0.00427 per °C. What is the winding resistance at full load?
0.298 Ω
Resistors are identified as to wattage by:
size
Derived units are obtained from various combinations of ______.
fundamental units