11. Lissajous pattern shown in a double-beam cathode-ray oscilloscope screen for two sinusoidal voltages of equal magnitude and of the same frequency but of phase shift of 30° electrical is
A circle
A straight line at 45°
An ellipse in the first and third quadrant
An ellipse in the second and fourth quadrant
Answer.3. An ellipse in the first and third quadrant
Explanation:
The Lissajous pattern on the screen of a CRO is an ellipse with a major axis in quadrant 1 and quadrant 3.
When two sinusoidal signals of the same frequency and magnitude are applied two both pairs of deflecting plates of CRO, the Lissajous pattern changes with the change of phase difference between signals applied to the CRO
When 0 < ϕ < 90° or 270° < ϕ < 360°
The Lissajous pattern is of the shape of an Ellipse having a major axis passing through the origin from the first quadrant to the third quadrant.
When 90° < ø < 180° or 180° < ø < 270°
The Lissajous Pattern is of the shape of an Ellipse having a major axis passing through the origin from the second quadrant to the fourth quadrant.
12. ________ is a Heart of Cathode Ray Oscilloscope (CRO).
Cathode Ray Tube (CRT)
Electron Gun
Amplifier
Sweep Generator
Answer.1. Cathode Ray Tube (CRT)
Explanation:
The cathode ray oscilloscope (CRO, for short) is a versatile laboratory instrument used for the visual observation, measurement, and analysis of waveforms. The heart or the major component of the oscilloscope is the cathode ray tube (CRT). The rest of the CRO consists of circuitry to operate the CRT.
13. A 1000 Hz sinusoidal voltage is connected to both X and Y inputs of a CRO. Which of the following waveforms is seen on CRO?
Sine wave
Circle
Ellipse
Straight line
Answer.4. Straight line
Explanation:
When the same signal is applied to the X-Y plate of CRO a straight line with slope = 1 is observed.
On the screen (Some signal means 0° angle diffusion).
Hence when a 1000 Hz sinusoidal voltage is connected to both X and Y inputs of a CRO. A straight line is observed in CRO.
14. A cathode ray oscilloscope typically has an input impedance of
1 GΩ
1 kΩ
1 MΩ
1 Ω
Answer.3. 1 MΩ
Explanation:
Practically input impedance of the cathode ray oscilloscope (CRO) has a range of megaohm (MΩ).
Practically input capacitance of the cathode ray oscilloscope (CRO) has a range of pico Farad (pF).
Input impedance, input capacitance, gain-bandwidth product & rise time all terms are associated with a vertical amplifier of CRO.
15. Which of the following can be used to measure RMS, peak, and an average value of an a.c voltage?
Hotwire instrument measures RMS value of AC voltage
The rectifier instrument measures the average value of AC voltage, but the scale is calibrated for RMS values
Megger is used to measure the high value of insulation resistance
Cathode ray oscilloscope (CRO) is used to measure RMS, peak, and average value of an AC voltage
16. An aquadag is used in a CRO to collect
Primary electrons only
Secondary emission electrons only
Both primary electrons and secondary emission electrons
Heat emission electrons
Answer.2. Secondary emission electrons only
Explanation:
The bombarding electrons, striking the screen, release secondary emission electrons
These secondary electrons are collected by an aqueous solution of graphite called Aquadag which is connected to the second anode
It is the conductive coating on the screen
The collection of secondary electrons is necessary to keep the CRT screen in a state of electrical equilibrium
17. While measuring the phase difference between the signals v1(t) = 10 sin ωt and v2(t) = 10 sin (ωt + ϕ), the Lissajous pattern observed on CRO is a circle. The value of ϕ is:
2π
π
π/2
π/4
Answer.3. π/2
Explanation:
In CRO we can measure the phase difference by X-Y mode operation.
At a phase shift ϕ = 0° or 360°, the pattern indicated by CRO is a diagonal straight line making 45° with the X-axis.
At a phase shift of ϕ = 90°, the pattern indicated by CRO is a clockwise rotating circle.
At phase shift ϕ = 180°, the pattern indicated by CRO is a diagonal straight line making 135° with the X-axis.
At phase shift ϕ = 270°, the pattern indicated by CRO is an anti-clockwise rotating circle.
18. Calculate the fastest rise time (in ms) a sine wave can have to be reproduced by a CRO if the bandwidth ranges from 0 Hz to 10 Hz.
17.5
0.35
35
1.75
Answer.3. 35
Explanation:
BW × rise time = 0.35
Given that, bandwidth (B.W.) = 10 Hz
Raise time tr = 0.5/BW = 0.35/10
tr = 0.035 s = 35 ms
19. Which of the following part is not located inside the cathode ray tube of the CRO?
Electron gun
Timebase generator
Vertical deflection plates
Horizontal deflection plates
Answer.2. Timebase generator
Explanation:
The CRO stands for a cathode ray oscilloscope.it consists of a set of blocks which are, shown in the following block diagram.
Subparts of Cathode Ray Tube are
Electron gun: It emits electrons and forms them into a beam with the help of a heater, cathode, grid, and pre-accelerating, accelerating, and focusing anode.
Vertical deflectionplates: VDP is applied with a test signal. Whose waveform has to be observed on the screen VDP is kept in a Horizontal position.
Horizontal deflectionplates: HDP is used for shifting the electron beam horizontally i.e. horizontal time scale is adjusted by changing HDP potential manually.
Screen: A standard screen size is 8 cm by 10 cm. The screen is coated with a phosphor that emits light when struck by the electron beam
Hence, the Time-base generator is a part of CRO but not a part of CRT.
20. Cathode of CRO is coated with
Alkali material
Thorium oxide
Copper oxide
Barium oxide
Answer.4. Barium oxide
Explanation:
The electron gun assembly of a CRO consists of an indirectly heated cathode, a control grid, a focusing anode and an accelerating anode and it is used to produce a focused beam of electrons.
The cathode consists of a nickel cylinder coated with oxide coating and provides a large number of electrons. It is associated with Barium or Strontium oxide.
