ELEC | COACHING NOTES Flashcards
The resistance of a wire is ‘R’ ohm. If it is melted and stretched to ‘n’ times its original length, what will be its new resistance?
A. R/n²
B. n/R1
C. R1/N
D. n²R₁
D. n²R₁
An iron ring 30 cm mean diameter is made of square of iron of 2 cm × 2 cm cross-section and is uniformly wound with 400 turns of wire of 2 mm² cross-section. Calculate the value of the self-inductance of the coil. Assume μ_r = 800.
A. 68.3 mH
B. 56.9 mH
C. 63.8 mH
D. 59.6 mH
A. 68.3 mH
Two coils A and B each having 1200 turns are placed near each other. When coil B is open-circuited and coil A carries a current of 5 A, the flux produced by coil A is 0.2 Wb and 30% of this flux links with all the turns of coil B. Determine the voltage induced in coil B on open-circuit when the current in the coil A is changing at the rate of 2 A/s.
A. 28.8 V
B. 30.4 V
C. 26.8 V
D. 24.9 V
A. 28.8 V
For a 1/8 watt resistor, what is the maximum allowable change in resistance for a 1000-hour rated load life test?
A. 5 %
B. 15 %
C. 10 %
D. 12 %
D. 12 %
A 400 mm length of conductor carrying a current of 25 A is situated at right-angles to a magnetic field between two poles of an electric motor. The poles have a circular cross-section. If the force exerted on the conductor is 80 N and the total flux between the pole faces is 1.27 mWb, determine the diameter of a pole face.
A. 13.1 mm
B. 12.4 mm
C. 11.3 mm
D. 14.2 mm
D. 14.2 mm
Wattage rating is maximum power that the resistor can dissipate assuming which of the following factors?
A. A specific life
B. A standard ambient temperature
C. A stated long term drift from its no-load value
D. All of the above
D. All of the above
What is a small capacitance formed by twisting together two insulated wires?
A. gimmick capacitance
B. stray capacitance
C. diffusion capacitance
D. junction capacitance
A. gimmick capacitance
Which of the following is not an industry standard in color coding potentiometer terminals for identification?
A. Blue
B. Yellow
C. Green
D. Red
A. Blue
A magnet moves inside a coil. Consider the following factors:
I. Strength of the magnet
II. Number of turns in the coil
III. Speed at which the magnet moves
Which can affect the emf induced in the coil?
A. III only
B. I only
C. II only
D. I, and II, III
D. I, and II, III
The motion of ion charges in a liquid or gas is called ______.
A. superconductivity
B. the corona effect
C. ionization current
D. hole flow
C. ionization current
What is the atomic radius of copper atom?
A. 1.41 Angstroms
B. 1.25 Angstroms
C. 1.17 Angstroms
D. 1.16 Angstroms
C. 1.17 Angstroms
In potentiometer terminal identification system, what color represents “always the clockwise element limit”?
A. Green
B. Yellow
C. Red
D. Blue
A. Green
For the magnetic circuit shown below, find the current I in the coil needed to produce a flux of 0.45 mWb in the air-gap. The silicon iron magnetic circuit has a uniform cross-sectional area of 3 cm² and its magnetizing force is 3500 A/m.
A. 0.84 A
B. 0.81 A
C. 0.83 A
D. 0.82 A
C. 0.83 A
A conductor moves with a velocity of 20 m/s at an angle of 90° to a magnetic field produced between two square-faced poles of side length 2.5 cm. If the flux on the pole face is 60 mWb, find the magnitude of the induced e.m.f. in each case.
A. 48 V
B. 47 V
C. 45 V
D. 49 V
A. 48 V
Which of the following capacitor terminology refers to the ratio by which the capacitance is increased when another dielectric replaces a vacuum between two electrodes?
A. Relative capacitivity
B. All of the choices
C. Dielectric constant
D. Relative permittivity
B. All of the choices
Dissipation factor is defined as the ratio of the energy dissipated to the energy stored in the dielectric. For what dissipation factor value, where it is considered equal to the power factor of the dielectric?
A. Equal to 1
B. Less than 0.1
C. Equal to 10
D. Greater than 0.1
B. Less than 0.1
What class of ceramic capacitors are stable temperature-compensating capacitors that have essentially linear characteristics with properties independent of frequency over the normal range?
A. Class I
B. Class IV
C. Class III
D. Class II
A. Class I
The figure shows the motion of electrons in a wire that is near the N pole of a magnet. The wire will be pushed:
A. upwards
B. downwards
C. toward the magnet
D. away from the magnet
A. upwards
An air capacitor has two parallel plates 10 cm² in area and 0.5 cm apart. When a dielectric slab of area 10 cm² and thickness 0.4 cm was inserted between the plates, one of the plates has to be moved by 0.4 cm to restore the capacitance. What is the dielectric constant of the slab?
A. 5
B. 3
C. 1
D. 7
A. 5
Find the magnetic field strength and the magnetomotive force needed to produce a flux density of 0.33 T in an air-gap of length 15 mm.
A. 3993 AT
B. 9393 AT
C. 3939 AT
D. 9339 AT
C. 3939 AT
An uncharged capacitor of 0.01 F is charged first by a current of 2 mA for 30 seconds and then by a current of 4 mA for 30 seconds. Find the final voltage in it.
A. 10 V
B. 18 V
C. 20 V
D. 15 V
B. 18 V
A magnetic circuit with a single air gap is shown in the figure below. The core dimensions are: Cross-sectional area Ac = 1.8 × 10¯³ m², Mean core length lc = 0.6 m, Gap length g = 2.3 x 10¯³ m, N = 83 turns. Assume that the core is of infinite permeability and neglect the effects of fringing fields at the air gap and leakage flux. Calculate the reluctance of the air-gap Rg for a current i = 1.5 A.
A. 1.17 x 106 A/Wb
B. 1.017 x 106 A/Wb
C. 1.71 x 106 A/Wb
D. 1.071 x106 A/Wb
B. 1.017 x 106 A/Wb
To apply the superposition theorem, all components must be ______
A. grounded.
B. both nonlinear and unidirectional.
C. both linear and bilateral.
D. the active type.
C. both linear and bilateral.
What is the relation of the electrical resistivity of ferrites to metals?
A. Ferrites have resistivities twice that of metals resistivity.
B. 10^3 times that of metals resistivity.
C. Ferrites have resistivities typically 10^6 times that of metals.
D. 10 times that of metal`s resistivity.
C. Ferrites have resistivities typically 10^6 times that of metals.
The fact that the sum of the individual branch currents equals the total current in a parallel circuit is the basis for _____.
A. Kirchhoffs voltage law.
B. Node-voltage analysis.
C. Kirchhoffs current law.
D. Method of mesh currents.
C. Kirchhoff`s current law.
A rectangular loop of wire has area A. It is placed perpendicular to a uniform magnetic field B and then spun around one of its sides at frequency f. The maximum induced emf is:
A. 2BAf
B. 4BAf
C. 2π BAf
D. 4π BAf
C. 2π BAf
Silicon becomes an extrinsic semiconductor with electrons as the majority carrier when doped with
Antimony
In intrinsic semiconductor, the formation of holes and free electrons increases with temperature and is known as _______.
thermal carrier generation
What static electricity is produced by rubbing fur on a rubber, amber or plastic rod?
Resinous static electricity
The electric field due to a uniform distribution of charge on a spherical shell is zero:
A. nowhere
B. only at the center of the shell
C. only inside the shell
D. only outside the shell
C. only inside the shell
An electric field strength created by charge Q is measured to be 40 N/C at a distance of 0.2 m from the center of the charge. What is the new field strength when the distance from the center of Q is changed to 0.4 m away with twice the charge of Q?
A. 10 N/C
B. 20 N/C
C. 30 N/C
D. 40 N/C
B. 20 N/C
When multiplying complex numbers in polar form, _____.
multiply the magnitudes and add the phase angles
For the circuit shown below, determine v_a.
8.67 V
What static electricity is produced by rubbing silk on a glass rod?
Vitreous static electricity
In an ac circuit with only parallel inductors.
A. I_T lags V_A by 90°
B. V_A lags I_T by 90°
C. V_A and I_T are in phase
D. none of the above
A. I_T lags V_A by 90°
What component of dielectric current is proportional to the rate of accumulation of electric charges within the dielectric?
A. Reactive current
B. Apparent Current
C. Inductive Current
D. Absorption current
D. Absorption current
What element property represents the relative tendency of an atom to attract shared electron pairs?
Electronegativity
What capacitor terminology includes power factor, loss factor, and dielectric loss?
A. quality factor
B. tangent of loss angle
C. cosine of loss angle
D. dissipation factor
B. Tangent of loss angle
If the magnetic flux through a certain region is changing with time:
A. an electric field must exist at the boundary
B. a current must flow around the boundary
C. an emf must exist around the boundary
D. a magnetic field must exist at the boundaryRead more on
C. an emf must exist around the boundary
What will be the equivalent resistance of the circuit shown in figure between two points A and D?
A. 10 Ω
B. 20 Ω
C. 30 Ω
D. 40 Ω
C. 30 Ω
Determine the transition capacitance of a diffused junction varicap diode at a reverse potential of 4.2 V if C(0) = 80 pF and V_T = 0.7V.
A. 41.82 pf
B. 3.48 pf
C. 13.33 pf
D. Data inadequate
A. 41.82 pf
Given Pmax = 14 mW for each diode, determine the maximum current rating of each diode (using the approximate equivalent model).
A. 10 mA
B. 20 mA
C. 15 mA
D. 25 mA
B. 20 mA
A charge Q is divided into two parts of q and Q – q. If the coulomb repulsion between them when they are separated is to be maximum, what should be the ratio of Q/q?
2:1
Which of the following does not contribute to the permanence of a magnet?
A. Crystal anisotropy
B. Minor phases
C. Grain growth
D. Cold working
C. Grain growth
An electron traveling north enters a region where the electric field is uniform and points west. The electron:
A. veers east
B. veers west
C. speeds up
D. slows down
A. veers east
Who invented the “electrophorus”, a device for storing an electric charge that replaced the Leyden jar?
Alessandro Volta
For the circuit shown, find i₁.
2.09 A
Which one of the following statements is incorrect at 0°K?
The valence and conduction bands of an intrinsic semiconductor overlap.
Which of the following statements is correct?
Semiconductivity is proportional to the product of the number and the mobility of carriers.
Determine the diode current at 20°C for a silicon diode with I_s = 0.1 µA at a reverse-bias potential of -10 V.
0.10 µA
What is the rms value of the wave shown in the figure?
A. about 95 V
B. about 80 V
C. about 50 V
D. about 25 V
B. about 80 V
For all resistor wattage ratings except 1/8 watt, what is the maximum allowable change in resistance for a 1000-hour rated load life test?
A. 10%
B. 5%
C. 15%
D. 12%
A. 10%
The B-H curve for _____ will be a straight line passing through the origin.
A. silicon steel
B. soft iron
C. hardened steel
D. air
C. hardened steel
In figure shown, what is the saturation collector current?
A. Vcc/R_E
B. Vcc/Rc - R_E
C. Vcc/Rc + R_E
D. Vcc/Rc
C. Vcc/Rc + R_E
Si transistor of the following figure has a α = 0.9 and I_CE = 0, V_EE = 5 V and Vcc = 13 V, then R_E will be ____ if I_EQ = 1 mA.
A. 4.3 kΩ
B. 5 kΩ
C. 3 kΩ
D. 4 kΩ
A. 4.3 kΩ
What is the time constant of the circuit in figure shown?
A. RC/2
B. 2/RC
C. RC
D. 1/2RC
A. RC/2
When a current source I is suddenly connected across a two terminal relaxed RC circuit at time t = 0, the voltage across the current source is shown in figure. The RC circuit is ______.
A. a parallel combination of R and C a series
B. combination of R and C
C. a pure capacitor
D. a series combination of R and parallel combination of R and C
D. a series combination of R and parallel combination of R and C
A capacitor terminology that refers to minute and rapid fluctuations of capacitance?
A. Burnout
B. Capacitance proofing
C. Coronation
D. Scintillation
D. Scintillation
In figure shown, v1 = 8 V and v2 = 4 V. Which diode will conduct?
A. D2 only
B. D1 only
C. Neither D1 nor D2
D. Both D1 and D2
B. D1 only
What if you have a 12-strand conductor and each strand has a radius (one-half the diameter) of 2/10 inch, what is the square mil area of the conductor?
A. 61,115 sq. mil
B. 45,239 sq. mil
C. 244,344,097 sq. mil
D. 1,507,965 sq. mil
D. 1,507,965 sq. mil
If the cross-sectional area of a magnetic field increases, but the flux remains the same, the flux density _______.
A. increases
B. remains the same
C. doubles
D. decreases
D. decreases
In the circuit shown below, the silicon npn transistor Q has a very high value of β. What is the required value of R2 in kΩ to produce Ic = 1 mA?
A. 40
B. 50
C. 30
D. 20
A. 40
In a CE amplifier the input impedance is equal to the ratio of _______.
A. ac emitter voltage to ac collector current
B. ac base voltage to ac emitter current
C. ac collector voltage to ac collector current
D. ac base voltage to ac base current
D. ac base voltage to ac base current
All but which one of the following statements regarding extrinsic semiconducting silicon is true?
A. Electrons are donated to the conduction band in n-type silicon.
B. The Fermi energy is raised by Group V elements in extrinsic silicon.
C. Group III elements accept electrons from the valence band of silicon.
D. The number of n-type carriers equals the number of p-type carriers
in extrinsic silicon.
D. The number of n-type carriers equals the number of p-type carriers
in extrinsic silicon.
If the steel disk in a crankshaft position sensor has stopped with the tab in the magnet’s air gap, the induced voltage ______.
A. increases
B. will remain constant
C. decreases
D. is zero
D. is zero
To prevent a DC return between source and load, it is necessary to use _______.
A. capacitor between source and load
B. inductor between source and load
C. either resistor between source and load or inductor between source and load
D. resistor between source and load
A. capacitor between source and load
The figure shows the self-bias circuit for CE amplifier and its equivalent circuit. What are V_BB and R_B respectively?
A. 2 V and 10 kΩ
B. 5 V and 4 kΩ
C. 2 V and 4 kΩ
D. 10 V and 4 kΩ
C. 2 V and 4 kΩ
In figure shown, what is the current supplied by battery immediately after switching on the circuit?
A. 4 A
B. 10 A
C. 0
D. 1 A
D. 1 A
In an ac circuit, what can be the maximum and minimum values of power factor?
A. 1 and 0
B. 2 and 0
C. 0 and -1
D. 1 and -1
A. 1 and 0
For the circuit shown below, different time constants are given:
- 0.5 x 10¯³ s
- 2 x 10¯³ s
- 0.25 x 10¯³ s
- 10¯³ s
What are the charging and discharging times respectively?
A. 1, 3
B. 2, 3
C. 2, 4
D. 1, 2
A. 1, 3
The amplifier circuit shown below uses a silicon transistor. The capacitors C_C and C_E can be assumed to be short at signal frequency and the effect of output resistance r_0 can be ignored. If C_E is disconnected from the circuit, which one of the following statements is TRUE?
A. Both input resistance Ri and the magnitude of voltage gain Av increase
B. The input resistance Ri decreases and the magnitude of voltage gain Av decreases
C. The input resistance Ri increases and the magnitude of voltage gain Av decreases
D. Both input resistance Ri and the magnitude of voltage gain Av decrease
C. The input resistance Ri increases and the magnitude of voltage gain Av decreases
In an R-C series circuit excited by a voltage E, the charge across capacitor at t = 0^+ is ______
A. CE
B. [1 - e^(t/RC)]
C. 0
D. infinity
C. 0
An RLC series circuit is underdamped. To make it overdamped, the value of R ______.
A. has to be reduced to zero
B. has to be decreased
C. has to be increased to infinity
D. has to be increased
D. has to be increased
The drift velocity of electrons is ______.
A. equal to speed of light
B. very small as compared to speed of light
C. half the speed of light
D. almost equal to speed of light
B. very small as compared to speed of light
The ‘h’ parameters of the circuit shown in the figure are h_ib = 25 Ω, h_fb = 0.999 and h_ob = 10¯⁶ Ω. What is the voltage gain?
A. 400
B. 100
C. 300
D. 200
A. 400
