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
Good engineering practice usually requires that a series-parallel resistive network be made:
From resistors that are all the same.
How much heat in kcal is produced by a current of 20 Amperes flowing for half of an hour in a circuit having a resistance of 6 ohms?
1032
The resistance of a copper wire at 30°C is 50 ohms. If the temperature coefficient of copper at 0°C is 0.00427°C^-1, what is the resistance at 100°C?
63.25
A copper bar is 1/2 inch by 4 inches by 20 feet. If the resistivity of the copper bar is 10.37 ohms-cmf, then what is the resistance of the copper bar?
8.1445 x 10ˉ⁵ Ω
If the reference point is changed to the earth point, then any voltage taken w.r.t. the earth is known as ____.
absolute potential
If a 220 V heater us used on 110 V supply, heat produced by it will be ____ as much
one-fourth
A wire with a smaller cross-sectional area will produce:
more heat
For a given line voltage, four heating coils will produce maximum heat when connected:
All in parallel
You have an unlimited supply of 1-W, 100-Ω resistors. You need to get a 100-Ω, 10-W resistor. This can be done most cheaply by means of a series-parallel matrix of:
4 x 4 resistors
Scientific notation is a method _____.
all of the choices
What is the size of 250MCM in square millimeter?
126.677
Four wires of same material, same cross – sectional area and same length when connected in parallel gives a resistance of 0.25 ohm. If the same four wires are connected in series, its effective resistance will be equal to ____.
4 ohms
A carbon resistor dissipates 60 watts of power from a 120-volt source at 20°C. How much power will be dissipated in the resistor at 120°C if connected across the same source? Assume that the temperature coefficient of carbon at 20°C is – 0.0005 per °C.
63.16 W
The power taken by a 500-ft resistive coil made of copper wire is 250 watts at 100 volts. The resistivity of copper is 10.4 ohm-cm per ft. Calculate the cross-sectional area of the coil in circular mil.
107
A 500 MCM ACSR cable has 37 strands. Determine the diameter in mils of each strand.
116.25
The resistance of two wires is 25 ohms when connected in series and 6 ohms when joined in parallel. The resistance of each wire is ____.
15 ohms and 10 ohms
Suppose you double the voltage in a simple dc circuit and cut the resistance in half. The current will become:
Four times as great
In a series-connected string of holiday ornament bulbs, if one bulb gets shorted out, which of these is most likely?
The current in the string will go up.
The presence of electric current is
only made known by the effect if
produces. Three important effects
are:
C. generation, chemical & electric
shock
It is a cell designed to produce
electric current and can be
recharged.
A. Secondary cell
Which is the best conductor of
electricity?
A. Aluminum
B. Silver
C. Copper
D. Carbon
B. Silver
What is the other term for American
Wire Gauge?
A. JIS
B. Brown & Sharpe
C. DIN
D. VDE
B. Brown & Sharpe