Electrical Measurements & Measuring Instruments Multiple Choice Questions on “Qmeter”.
1. Q factor is called __________
a) Quality factor
b) Quantity factor
c) Queen factor
d) Quarter factor
Answer: a
Clarification: Q factor is also known as Quality factor or storage factor. It is basically a ratio of the power stored in an element to the power dissipated in that element.
2. Q factor is also defined as the ratio of _______
a) resistance to reactance
b) reactance to resistance
c) power to voltage
d) current to power
Answer: b
Clarification: Q factor can also be obtained as the ratio of reactance to resistance of an element. For inductive element it is the ratio of XL to R and for a capacitive element it is the ratio of XC to R.
3. What is a Q meter?
a) quality meter
b) quantity meter
c) instrument
d) detector
Answer: c
Clarification: Q meter is basically an instrument that is used for the measurement of electrical properties of capacitors and coils. It is also used as a laboratory instrument.
4. Q meter works on the principle of _______
a) barkhausen criterion
b) piezoelectric effect
c) parallel resonance
d) series resonance
Answer: d
Clarification: Q meter basically operates on the characteristics of a series resonant coil. In a series resonant circuit the voltage drop across the coil or a capacitor is equal to the applied voltage multiplied by its Q factor.
5. Q factor for a series resonant circuit is?
a) Q = (frac{X_L}{R} = frac{X_C}{R})
b) Q = XL R = XC R
c) Q = (frac{R}{X_L} = frac{R}{X_C})
d) Q = (frac{1}{R})
Answer: a
Clarification: Q factor in a series resonant circuit is given by the relation,
Q = (frac{X_L}{R} = frac{X_C}{R})
where, R is resistance of the coil
XC is the capacitive reactance
XL is the inductive reactance.
6. What is the relation between Q factor and voltage?
a) Q = (frac{1}{E})
b) Q = (frac{X_L}{R}=frac{X_C}{R}=frac{E_C}{E})
c) Q = E
d) Q = (frac{R}{X_L}=frac{R}{X_C}=frac{E}{E_C})
Answer: b
Clarification: The applied voltage E is inversely proportional to the Q factor of a circuit and is given by the relation,
Q = (frac{X_L}{R}=frac{X_C}{R}=frac{E_C}{E}).
7. A practical Q meter consists of __________
a) Wien bridge oscillator
b) AF oscillator
c) RF oscillator
d) Crystal oscillator
Answer: c
Clarification: Practically a Q meter consists of a wide range RF oscillator with a frequency range of 50 kHz to 50 MHz. Oscillator acts as a source and delivers current to a low shunt resistance.
8. Voltage across the shunt is measured by ________
a) voltmeter
b) multimeter
c) thermocouple
d) thermometer
Answer: c
Clarification: A thermocouple is used for measuring the voltage across a shunt resistance in a practical Q meter. Electronic voltmeter is used for the measurement of voltage across a resonant capacitor.
9. Inductance of the coil is ________
a) L = (frac{1}{(2πf)C})
b) L = (frac{1}{(2πf)^2})
c) L = (frac{1}{C})
d) L = (frac{1}{(2πf)^2 C})
Answer: d
Clarification: Coil inductance in a Q meter is given by the relation,
L = (frac{1}{(2πf)^2 C})
where, f is the frequency in Hz
C is the capacitance in F.
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